DTM Surfaces in Surpac Vision January 2007
Copyright © 2007 Surpac Minex Group Pty Ltd (A Gemcom Company). All rights reserved. This software and documentation is proprietary to Surpac Minex Group Pty Ltd. Surpac Minex Group Pty Ltd publishes this documentation for the sole use of Surpac licenses. Without written permission you may not sell, reproduce, store in a retrieval system, or transmit any part of the documentation. For such permission, or to obtain extra copies please contact your local Surpac Minex Group Office. Surpac Minex Group Pty Ltd Level 8 190 St Georges Terrace Perth, Western Australia 6000 Telephone: (08) 94201383 Fax: (08) 94201350 While every precaution has been taken in the preparation of this manual, we assume no responsibility for errors or omissions. Neither is any liability assumed for damage resulting from the use of the information contained herein. All brand and product names are trademarks or registered trademarks of there respective companies. About This Manual This manual has been designed to provide a practical guide to the many uses of the software. The applications contained within this manual are by no means exhaustive as the possible uses of the software are only limited by the user’s imagination. However, it will give new users a starting point and existing users a good overview by demonstrating how to use many of the functions in Surpac Vision. If you have any difficulties or questions while working through this manual feel free to contact your local Surpac Minex Group Office. Contributors Rowdy Bristol Kiran Kumar Phil Jackson Surpac Minex Group Perth, Western Australia Product Surpac Vision v5.2
Table of Contents Introduction ................................................................................................................................ 1 Requirements ............................................................................................................................ 1 Objectives .................................................................................................................................. 1 Workflow .................................................................................................................................... 1 Surface Modelling Concepts...................................................................................................... 2 Creating a DTM ......................................................................................................................... 7 Viewing DTMs.......................................................................................................................... 12 DTM Volume Calculations ....................................................................................................... 20 Applying a boundary string to trim a DTM ............................................................................... 30 Sectioning a DTM .................................................................................................................... 34 Draping a String Over a DTM .................................................................................................. 41 Image Draping ......................................................................................................................... 43 DTM / DTM Intersections......................................................................................................... 48
Introduction Surface Modelling allows us to use triangulation to create two-dimensional models known as Digital Terrain Models (DTMs). This document introduces the theory behind surface modelling processes and provides detailed examples using the surface modelling functions in Surpac Vision. By working through this manual you will gain skills in the construction, use of and modification of DTMs.
Requirements This tutorial assumes that you have a basic knowledge of Surpac Vision. We recommend that you be at least comfortable with the procedures and concepts in the Introductory Guide to Surpac Vision training manual. If you are a new Surpac Vision user, you should go through the Introductory Guide to Surpac Vision training manual before going through this manual. You will also need: • • •
To have Surpac Vision v5.2 installed on your computer The data set accompanying this tutorial Basic knowledge of Surpac string files and editing tools
Objectives The objective of this tutorial is to allow you to work with some Surface Modelling tools. It is not intended to be exhaustive in scope, but will show the work flow needed to achieve results. You can then refine and add to this workflow to meet your specific requirements.
Workflow
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Surface Modelling Concepts A digital terrain model (DTM) is made up of a surface joining adjacent strings. It is formed as a combination of those string lines, and of lines joining points on strings.
The joining process continues until the surface consists only of non-overlapping triangles. The software chooses the joins to produce the best-conditioned triangles - ie. those closest to equilateral triangles.
The resulting DTM can be thought of as an undulating patchwork quilt made up of triangular patches.
A Digital Terrain Model (DTM) is how Surpac models surfaces. Surfaces are used in Surpac for such things as 3D visualization and for calculating volumes. Almost any superficial feature can be modelled as a DTM, including natural topography, lithological contacts, bedrock/overburden contact, or water tables.
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DTMs must come from String data. String files contain the raw data, whereas DTM files contain a mapping of trios of points in the String file that constitute a triangle. DTMs are made of triangles, with each point of each triangle matched to a point in the original String file. Consequently DTM files are not valid without the original String files. That is, a DTM file cannot be opened if the original String file of the same name is not accessible. Another rule for the construction of DTMs is that DTMs cannot fold back on themselves. That is, a DTM cannot have multiple Z values for a given X, Y coordinate. Therefore you cannot model overhanging or vertical surfaces.
If the surfaces are to be used for further processing, such as for calculating volumes or higher end functionality within the surface menu, then the object must be named object 1 trisolation 1. It is important to consider this when creating the surface, as each surface must then be placed in a separate file.
1. Nomenclature The objects you create in Surpac Vision are numbered by a system analogous to that of string and string segment numbers. String Æ Segment Æ Point Æ
object trisolation triangle
When you define an object you explicitly assign it both an object number and a trisolation number. The object is then always referred to by the object and trisolation number originally assigned. The object number may be any in the range of 1 to 32000. The trisolation number may be any positive integer.
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DTM Conventions: • • •
DTMs cannot model overhangs or vertical surfaces DTMs must have one surface to a layer You must differentiate between spot heights and breaklines
Firstly we will look at the use of strings to act as break lines. Breakline strings are those which represent physical features that you can see in the real world e.g. crest of a pit, a fault in a geological model, a contour in a pit. If a string file has been formed correctly, then no breakline strings will cross over other breakline strings, unless the two strings cross at a common point as shown below.
Spot height strings contain random points which, when connected by a string line, do not represent any physical feature eg. randomly surveyed points, borehole collars.
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When modelling surfaces with DTMs, it is important that no triangles are formed across any breakline strings. If however, the string data consists of spot heights only, then the triangles will be formed in the most robust manner without taking into account any strings between the points.
2. Graphical vs File-based options A digital terrain model can be created in two ways to best suit the data you wish to model. Graphical creation of a DTM allows you to view your results immediately, however, for large data files the processing time may be prohibitive. The file-based tools allow you to perform the creation directly on the file data, saving both memory usage and creation time. The diagrams below show how to choose the functions used to create DTMs, firstly from a graphics based function, then for a file-based function
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Creating a DTM Overview It is important to understand how a string file relates to a dtm. Once a dtm has been created, any modifications to the string file will make the DTM invalid. Hence, if modifications are made to string data, you will need to recreate the DTM.
1. Graphical Creation Open the file topo1.str in Graphics From the Surfaces menu, select Create DTM from layer.
Click Apply on the form to create a DTM surface. Since the data you are working on is a copy of the original data, the file must always be saved after the DTM creation. From the File menu, select Save, then String/DTM, to save the DTM file Enter the data as shown below, then click Apply.
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Because the string file and dtm already exist, you will be asked if you wish to replace them. Click Yes.
Your results should like the diagram below:
If you want to see all of the steps performed in this chapter, either run or edit: _01a_create_DTM_from_layer.tcl Note: You will need to Apply the forms presented.
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2. File based DTM creation We will now create a DTM from the string file pit1.str using the file based DTM creation option. We will use this function to demonstrate the impact of using strings as breaklines. From the Surfaces menu, select DTM File functions, then Create DTM from string file. Fill in the form as shown below, then click Apply.
Note: The Strings to act as break lines checkbox is NOT ticked Note: The ability to clip to a boundary string at the same time as creating the DTM is new functionality introduced in Surpac Vision V5.2D. In earlier versions, or if you wish to clip a DTM from a string file after the DTM has been created, use the function Clip DTM from boundary string under the DTM file functions menu.
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Open the file pit1.dtm in Graphics. You should see something similar to that shown below:
Note that there are several triangles in the dtm that do not reflect the results we desire. We will now repeat the procedure, but using strings to act as breaklines. From the Surfaces menu, select DTM File functions, then Create DTM from string file. This time ensure that the checkbox for Strings to act as break lines is ticked. Fill in the form as shown below and click Apply.
•
The message window informs you of the processing as the DTM is created. When processing is finished, you will see a log file, which is a small report containing information about your DTM. Close the file to continue.
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The DTM file is saved automatically as pit1.dtm.
Open the file pit1.dtm in Graphics. You should see something similar to that shown below:
If you want to see all of the steps performed in this chapter, either run or edit: _01b_create_DTM_from_string_file.tcl Note: Whenever the macro pauses, displaying Click in graphics to continue in the message window, you will need to click in the graphics area to continue. Also, you will need to Apply any forms presented.
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Viewing DTMs 1. Colour a DTM by Elevation Open the file pit1.dtm by dragging it into Graphics. From the Display menu, select DTM with colour banding to display colour contours. Viewing the DTM by drawing shells is another method of displaying DTMs. Drawing shells and using false colouring of triangles is very similar to contouring your data. You can nominate to draw shells by: • •
specifying the number of bands setting the band width
Enter the parameters on the form as shown below and click Apply.
As you have nominated to display bands every 20 metres, the image on screen represents the following: •
blue
0 to 20 metres
•
green
20 to 40 metres
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yellow 40 to 60 metres
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red
60 to 80 metres
and then the colours repeat and so we have
•
blue
80 to 100 metres
and so on…
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Your result should look something like the image below:
If you want to see all of the steps performed in this chapter, either run or edit: _02_colour_DTM_by_elevation.tcl Note: You will need to Apply the forms presented.
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2. Creating a Fly-through Movie We will now digitise a string to follow and use the View along string function which allows us to effectively fly in the direction of the string. This is an excellent method for viewing terrain models. Reset graphics by clicking on the
icon.
Drag and drop the file eom_pit.dtm into Graphics.
First, we will apply colour banding to produce a realistic effect for our DTM display. Fill out the form as shown below, then click Apply.
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Now we will exaggerate the relief to make the flythrough more realistic. From the View menu, select Data view options, then View scale factors.
Fill in the form as shown below, then click Apply.
You will now digitise the line that you wish to fly along. The first step is to set the string number for any digitising that will be done. On the status bar at the bottom of the screen, click on the design string icon
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Set the string number to 500, then click Apply.
Next you will create a new layer for the new digitised string.
On the toolbar, select the layer selection box, and click on the option.
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Enter the name of the new layer as shown below, then click Apply.
The digitised string will be placed into this layer. The final step before you start creating your line is to tell Surpac that when you digitise a point it should snap onto the DTM surface. From the toolbar, select the snapping list options and click on the Triangle option.
Now you are ready to digitise your line. On the toolbar, select the icon. Now you can digitise your line. If you wish to window in you can do so at any time, and then start the digitising again by clicking on the icon again.
Once you have digitised your line, you should save the string file. Save the file as fly1.str. It is also useful to smooth the string out. This will remove any sharp turns in the line. From the Edit menu, select String, then Smooth. Fill in the form as shown below, then click Apply.
Save the file again. Now you can run the View along string function. From the View menu, select Data view options, then View along a string.
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This will display a form with the viewing options.
Select the along string option on the left. In the middle of the form, enter a camera field width of 100, a Camera Z offset value of 20 to lift the camera 20m above the ground and a Max frame distance as 5. The bigger this distance, the faster the camera will move along the string. Click on the Apply button and then click on the first point of the fly string.
Any time you wish to run the animation again, click on Zoom All, and then go to the View along string function as shown earlier. If you want to see all of the steps performed in this chapter, either run or edit: _03a_fly_through.tcl Note: You will need to Apply the forms presented.
Saving the images to make a movie.
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Run the View along string function again, but this time on the right of the form, enter a name to be given to the images that will be saved at set points Note: This process will produce many output files so we have changed the Max. frame distance to capture an image every 20 metres.
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You can set the number of pixels to higher resolutions than the default if required. This will create better images, but will also create bigger files for each image. This option creates a very large number of files, so be careful about how much memory you have free on you computer. If you want to see all of the steps performed in this chapter, either run or edit: _03b_fly_through_save_images.tcl Note: You will need to Apply the forms presented.
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DTM Volume Calculations 1. Create a boundary string We will now look at creating a boundary string of the pit to be used in volume calculations. A boundary string file can be used for: • • •
delineating cut and fill material for calculating volumes finding the intersection of a fault plane with a surface finding where a pit design breaks the natural surface.
There are two ways to create the boundary string in Surpac Vision, either file-based or graphics based. In the file-based method, there is no need to display the DTMs and the boundary string is automatically saved to the nominated file. In the graphics-based method, the DTMs must be displayed in graphics and the boundary string is not automatically saved but is simply displayed in its own graphics layer. You must save your boundary string to a file after it is generated.
File-based method Firstly, we will look at the file-based method. In this case, we will display the DTMs only for clarity. Open the files pit1.dtm and topo1.dtm in graphics. Note that the pit extends past the natural topography. To determine the volume of the pit, we need to define the boundary where the topography cuts the pit design, otherwise our volume estimates will be incorrect. We do this by creating a boundary string of the intersection between both DTMs.
From the Surfaces menu, select DTM File functions, then Line of intersection between two DTMs.
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Once we have the boundary string we can use it to constrain our volumes calculation. On the form below, fill in the names of the DTM files you wish to find the intersection of, then define the output string file you wish to create. Complete the form as shown below, then click Apply.
Once this for has been processed, a message will appear in the message window and the string will be displayed in graphics If you want to see all of the steps performed in this chapter, either run or edit: _04a_create_boundary_string_file_based.tcl Note: You will need to Apply the forms which are presented.
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Graphics-based method This process can also be completed graphically. In this case we MUST have the DTMs displayed in graphics as the function uses graphics layers to determine its input and output Open topo1.dtm and pit1.dtm in graphics From the Surfaces menu, select Clip or intersect DTMs, then Line of intersection between two DTMs. Complete the form as shown below, then click Apply.
This outputs the same result as the file based functions, but the fields can be selected graphically. In the graphics-based method, you need to save the string in the intersection layer to a string file if you wish to use it for further processing. After applying this form the result is displayed in the graphics and should look something like the diagram below:
If you want to see all of the steps performed in this chapter, either run or edit: _04b_create_boundary_string_graphics_based.tcl Note: You will need to Apply the forms which are presented.
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2. Cut and Fill Between DTMs We will now use the function Cut and fill between DTMs function from the Volumes menu to calculate the surface-to-surface volume between pit1.dtm and topo1.DTM and create a resulting volume report. One of the most common uses of DTMs is to calculate volumes. The DTM Volumes function allows you to compute the volume between two DTM surfaces, contained within a boundary string. From the Volumes menu, select Cut and fill between DTMs. Fill in the form as shown below then click Apply.
You should see something like the following:
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Create a DTM of the file dhc2.str which is a survey of drill hole collars prior to mining and will be used to model the natural surface. From the File menu, select Reset graphics or click on the
icon.
Open the string file dhc2.str by dragging it into Graphics. This file is a survey of drill hole collars prior to mining and may be used to model the natural surface. Notice that the file consists of one spot height string. From the Surfaces menu, select DTM File functions, then Create DTM from string file.
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Complete the following form:
Note that when creating a DTM by the file based method, we can turn off the option 'Strings to act as break lines. The result is saved as dhc2.dtm. We will now create a DTM of the file pit2.str using spot heights and using the breakline test Load the file pit2.str in graphics and display the string numbers to determine if there are any spot height strings. String 9999 consists of spot heights and can be used during the creation of the DTM. From the Surfaces menu, select DTM File functions, then Create DTM from string file.
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Complete the following form:
The result is saved as pit2.dtm. Using these two files, we will calculate the volume between the two surfaces. From the Volumes menu, select Net volume between DTMs. Enter the parameters as shown below, then click Apply. Note: String #2 of pit2.str can be used as a boundary string for the volume calculation.
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Complete the form shown below, then click Apply. This defines the output file name and format for the report.
Apply the blank form as shown below:
The results from the DTM volume calculations can be saved to a .csv file and optionally to a boundary string file. This string file contains details of the calculations in the Description Fields. The results that are saved to the D fields and the order in which they are saved are described below. These values can be found starting with the D1 field. •
slope area of first DTM
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slope area of second DTM (only if 2 DTMs are used)
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area of boundary segment
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volume between 2 DTMs (or between the first DTM and datum plane z=0)
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average thickness (volume/area of boundary segment)
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total of first quality parameter (if it is used)
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average value of the first quality parameter (only if it used)
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total of the second quality parameter (only if it is used)
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average value of the second quality parameter (only if it is used).
Next you will be prompted to save the modified files. Save the modified DTM.
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Because you use a boundary string to calculate DTM volumes, triangles which lie outside the boundary string are deleted. Hence the prompt to save the modified DTM. The first DTM is dhc2 and there is no point in saving this file, so simply Apply the blank form.
Once again a prompt to save the modified DTM is presented, this is for the second DTM pit2. Apply the blank form as we do not need to save this file.
If you want to see all of the steps performed in this chapter, either run or edit: _05_cut_and_fill_volumes.tcl Note: You will need to Apply the forms which are presented.
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The volume report results shown below are in the file pit2.csv, which will be displayed on the screen.
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Applying a boundary string to trim a DTM This function uses a boundary string to trim a DTM. The boundary string may consist of any number of closed segments and may contain clockwise and internal anticlockwise segments, (i.e. representing pillars or waste volumes). This function is used to prepare a file for viewing in solids modelling or contouring within a restricted area.
1. File Based Method Firstly we will look at applying a boundary string to trim a DTM using file based data. From the Surfaces menu, select DTM File functions, then Create DTM from string file. Fill in the form as shown below, then click Apply.
In this case, we are using the same string to clip the dtm as was used to define the boundary of the dtm. Since the operation was performed directly on the input files, there is no need to save the DTM file. Open the file back1665.dtm by dragging it into Graphics. You will see that the DTM has been clipped to the borders defined by the back1665.str string file. The ability to clip to a boundary string at the same time as creating the DTM is new functionality introduced in Surpac Vision V5.2D. In earlier versions, or if you wish to clip a DTM from a string file after the DTM has been created, use the function Clip DTM from boundary string under the DTM file functions menu. If you want to see all of the steps performed in this chapter, either run or edit:
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_06a_clip_dtm_file_based.tcl Note: You will need to Apply the form which is presented.
2. Graphics based method Now we will look at a method that uses the data displayed in graphics to clip the DTM. Note that the file lev1665.str represents the same data as in back1665, but dropped 6 metres in the z direction using string maths. Open the string file lev1665.str by dragging it into Graphics Rotate the image within graphics to view the file. It should look like the image below:
This represents the pickup of some underground workings. From the Inquire menu, select Segment properties, and select a number of points on the string, note that the pillars are all anti-clockwise and the drives are all clockwise. From the Surfaces menu, select Create DTM from layer and Apply the confirmation form.
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Save the resultant DTM to a file lev1665.dtm.
Note that when the DTM was created, no distinction was made between clockwise or anticlockwise strings. The result is a rather untidy DTM which does not properly model the original survey data. By using the floor string as a boundary string, the anti-clockwise segments will act as areas of exclusion The DTM Clip function does exactly this. From the Surfaces menu, select Clip or intersect DTMs, then Clip DTM with string. Select a point on the string to perform the clipping operation. Save the resultant data to DTM file lev1665.dtm.
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Note how the triangles outside the boundary strings have been clipped. This is one way of beginning to create a 3D model of these underground workings. If you want to see all of the steps performed in this chapter, either run or edit: _06b_clip_dtm_graphics_based.tcl Note: You will need to Apply the forms which are presented.
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Sectioning a DTM This function allows you to create horizontal, vertical or inclined sections through a surface The plane of intersection of the sections is defined by entering the Y, X, Z coordinates at each end of a three dimensional axis line and by specifying the interval along that axis at which sections are to be taken. The first section is taken at the start of the axis and then sections are taken at the specified intervals along the axis until the length of the axis is reached.
1. Create DTM sections Open the file pit1.dtm by dragging it into Graphics. From the Create menu, select Section axis by coordinates. Fill in the form as shown below to create a section axis line.
From the Surfaces menu, select Create sections from DTM. Fill in the form as shown below and click Apply.
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Then fill in the next form ( or accept values from previously defined section axis line) to define the axis line and click Apply.
Note: The axis start is the co-ordinates for the starting point of the axis line. The first section is extracted at this starting point. The axis end is the end point of the axis line. Sections may be extracted either perpendicular to the line defined by the start and end points or parallel. Sections will not be extracted past the axis end point. The result produced by this function is a range of string files, named dtm_section7000 to dtm_section7600 in steps of 100, which contain the extracted sections in section coordinates. These files are automatically saved to disk. You should see something like the diagram below. Note that the axis line is displayed in the left pane. In the right pane are the resulting sections, displayed in section coordinates.
The segments produced from the Create sections from DTM function will have the same string number as the object number from which they were extracted. The segments produced may be either open or closed segments. Closed objects will always produce closed segments when they are sectioned, whereas open objects may produce either open or closed segments. Closed objects are significant, because the sections generated from sectioning a closed object can automatically be used for further processing where closed segments are required.
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There is also a file-based sectioning function. It may be accessed through the Surfaces menu, by selecting DTM File functions, then Create sections from DTM. This function removes the need to load DTM files (which can be very large) into Graphics The diagram below shows how to invoke the file based version.
If you want to see all of the steps performed in this chapter, either run or edit: _07a_create_section_axis_line.tcl _07b_sectioning_pit.tcl Note: You will need to Apply the forms which are presented.
2. Create DTM contours We will now look at how to section the pit by elevation, creating contours every 10 metes on the file pit1.dtm. Open the file pit1.dtm by dragging it into Graphics. We now wish to extract or create contours by elevation for every 10 metres within the pit. Optionally, you can click on the icon to plot a 2D grid over the area if you want to determine the minimum and maximum extents of the pit. Note that the form automatically shows that the elevation of this DTM goes from 45 to 245 metres. From the Contouring menu, select Contour DTM in layer. Fill in the form as shown below and click Apply.
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If you wish to save the sectioned string file, change your active layer to section and then save the file.
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If you want to see all of the steps performed in this chapter, either run or edit: _07b_section_pit_by_elevation.tcl Note: You will need to Apply the forms which are presented.
3. Contour Extract This function extracts contours from a DTM and then stores them in a string file for viewing or plotting. The contours are created by interpolating line segments across all of the triangles and then joining them into continuous strings. The contours will exactly correspond to the original data from which the DTM was created. These contours can then be used for plotting or for volume calculations or polygon intersections with other string files. If contours are required for volume calculation or polygon intersection they must be closed strings. You must ensure that the original DTM is constructed so as to guarantee this will happen. Usually this will involve adding an extra boundary string enclosing the string data within the DTM but with a Z value just greater than the maximum Z value in the data (in the case of a pit,) or just less than the minimum Z value in the data (in the case of a stockpile). We will now look at an example. From the Contouring menu, select Contour DTM file. Fill in the form as shown below , then click Apply.
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Fill in the form as shown below and click Apply.
Define the method that you wish to create the contours. Interval: The contours to be extracted will be defined by entering an interval with a minimum and maximum contour value. Range: The contours to be extracted will be defined by entering a range. Unlike the Interval method which guarantees that contours will be at integral multiples of the contour interval, this method permits you to define the contour levels of interest precisely. It is therefore possible to create contours at intervals of 2 but starting from a non-integral multiple of 2. e.g. 147.5, 149.5 etc. This method also permits you to extract contours at irregular intervals thus making it possible to extract contours at values of particular interest.
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Define the plot enhancement requirements Create index contour file If you intend to use the contours for plotting, you may wish to plot the index contours (or contours at some specific interval) in a different colour to other contours. For example, if contours were extracted at intervals of 2, then index contours would probably be at intervals of 10, that is 10, 20, 30, etc. These index contours may be saved to an Index contour string file thus making it easy to plot the index contours using a different colour on a hardcopy map. If you choose to create an index contour file, then the index contours will not be in the contour string file at all, they will only appear in the index contour file.
Produce contour annotations If you choose to create contour annotations then a string file will be created which contains data suitable for use by the Plotting module for labelling the contour strings, at the mid point of the each contour, with the contour values. This string file will consist of pairs of points. Each pair of points will be aligned with a small portion of the contour string, in the middle of the string, with the contour value in the D1 field of the second point in each pair of points. String 1 in the annotation string file will contain all the annotation data for the Normal contours while string 2 will contain the annotation data for the index contours.
If you want to see all of the steps performed in this chapter, either run or edit: _08_extract_contours.tcl Note: You will need to Apply the forms which are presented.
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Draping a String Over a DTM Open the file topo1.dtm by dragging it into Graphics. Also open the file dhcollar1.str in graphics. From the Customise menu, select Display properties, then Strings and points. Change the drawing method to marker as shown in the form below to display the string as spot heights.
Note that the drillhole collars are currently at an elevation of 300m. To determine the correct elevation of the drill hole, we will drape the drill hole collars onto the topography to determine the point of intersection.
From the Surfaces menu, select Drape string over DTM.
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Click on one of the markers to select the string to drape over the DTM. Ensure that you uncheck the Interpolate New Points checkbox in the form presented.
Your results should look something like the image below. Note how the drill holes have now been draped over the topography.
If you want to see all of the steps performed in this chapter, either run or edit: _09_drape_string_over_dtm.tcl Note: You will need to Apply the forms which are presented.
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Image Draping This function permits you to apply advanced rendering techniques to DTMs by draping an image file over the model. Surpac allows you to use GIF, jpeg, tif, png or bmp files as images to drape over your DTM. This technique is very useful: •
When an aerial photograph has been scanned and saved in a image file and you wish to drape it over a DTM of the surface to give a photo-realistic representation of the land surface. This technique requires you to digitise a number of control points, known as registration points in the image and in the DTM.
•
When you want to display solid models of ore bodies with a texture appropriate for rock type which it represents. In this case, you require a image file of a suitable texture which is then 'tiled' over the model.
Note: This technique requires some effort to produce good results. Matching points in the image and the DTM must be selected with care, otherwise the image will not match the DTM. The co-ordinates of the control points may be saved to a registration file (.rgf) to simplify future image rendering. Open the file eom_pit.dtm by dragging it to graphics. From the File menu, select Images, then Drape an Image file over a DTM. The prompt at the bottom of the screen will say ask you to Select the triangle of interest. Select a triangle on the trisolation to which the image file is to be applied to display the Drape Image over a DTM or Trisolation form as shown below:
The registration file stores the parameters used for registering a image file over a DTM so that the image can be made to match the DTM precisely. In addition to the name of the image file
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and the filter colour, the registration file records the image coordinates (X and Y pixel values) and the corresponding real world coordinates for each of the registration points. If you are using either of the tiling options then any file name which you might enter into this field has no effect on the result. A minimum of 3 registration points are required and a maximum of 100 can be used. As more registration points are used, the image will develop a progressively better match with the DTM. Enter a name to create a new registration file. If the registration file named does not exist then it will be created and all the details are saved to it after the registration points have been defined. If the registration file already exists, the parameters are displayed on the form to permit you to alter them to suit your requirements. Registration files are commonly used to simplify the task of draping an image over a DTM as defining registration points repeatedly for the same image/DTM can be quite time consuming. Image file This is the image file which contains the image to be draped over the DTM. Image draping method The image can be draped over the trisolation using one of two different methods, with each method having two variations. These methods are:
1. Registering the image. This is where the image and the DTM over which it is to be draped are displayed side by side, in different viewports. Matching pairs of points are selected, using the mouse, to control the process of draping the image over the DTM. This method is most suitable when the image is of an aerial photograph and the DTM is the land topography at the time the photograph was taken. The two variations for this method are: • register with new points This method will use whatever registration points are displayed in the registration points scrolling region and will require more registration points to be defined. You may find that this method will be used a number of times with an image and DTM to progressively improve the match between the image and the DTM. • register with existing points This method will only use the registration points displayed in the registration points scrolling region. If fewer than 3 registration points are present in the scrolling region when you click Apply, you will be required to define some more registration points.
2. Tiling the image This is where the image is given dimensions, in the real world X and Y directions, and the image is tiled over the selected trisolation in tiles of these dimensions. This method is useful for applying images of different material textures to make solid models of ore bodies, for example, appear more realistic. The best results will be achieved with images which have no obvious pattern especially when tiling over solid models as the image may be distorted considerably when folding underneath the solid model.
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The two variations for this method are: • tiling This tiling method simply places the image in tiles of the specified size over the trisolation. • mirror tiling This tiling method creates a mirror image of every second tile, in both the X and Y directions. Define registration points by When using registration points, you always use the mouse to select the registration point locations in the image. To define the registration point coordinates in the DTM however you may choose from: Graphics The mouse is used to select the location of the registration point on the DTM. Use this method when only approximate locations for the registration points are known or when surface features, roadway intersections for example, are being used.
Keyboard The coordinates of the registration points are entered into a form. This method is appropriate when the registration points are surveyed targets which are clearly identifiable. Transmission colour The textured image may be made transparent by specifying a transmission colour. This colour is allowed to shine through the textured object when another object falls behind it. Best results can be obtained by using grey. Ambient colour Some graphics cards adaptors may cause a dimming of the textured image. This can be countered by specifying an ambient colour that is reasonably light in colour. To cancel the effect of the transmission colour and ambient colour as applied by the Image Drape function, you can use either the Clear Screen or Erase Objects functions.
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Image colour filter The image colour filter works in a manner similar to colour filters in photography. By leaving the colour filter blank, the image is presented in the colours as defined in the image file. Image and Real World coordinates for registration points If an existing registration file is being used, all the saved parameters, including previously defined registration points are displayed here. There must be a minimum of 3 registration points to register the image to the DTM with the maximum number of registration points being 100. Complete the Drape Image over a DTM or Trisolation form and click Apply to either drape the gif image over the selected trisolation or to define registration points for controlling the image registration process. The registration points must now be defined by selecting a location in the image. Digitise the registration point # in viewport 2 Locate the mouse over the required point in the image and press the mouse button to define the image coordinates for a new registration point. The following prompt will be displayed: Digitise registration point # on the DTM in viewport 1 Locate the same point in viewport one and press the mouse. After digitising the location of the registration point in the DTM or entering the coordinates of the registration in the Define coordinates for image registration point form, you will be prompted to digitise another registration point. When sufficient registration points have been defined, press Escape to display the Review registration point coordinates form. These are the real world coordinates of the corresponding locations for registration points in the DTM. Complete the Review registration point coordinates form and choose Apply to drape the image over the selected trisolation.
If you want to see all of the steps performed in this chapter, either run or edit: _10_image_draping.tcl Note: You will need to Apply the forms which are presented.
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Helpful Hints Adjusting the view When defining the registration points either in the image or in the DTM, it is generally necessary to adjust the view by either windowing in or out to find the best location for the registration point. By pressing the Assist key, generally F11 you can invoke the Viewer to adjust the view. On exiting from the Viewer, you will be prompted to select the point of interest. Resizing the viewports The original viewport containing the selected trisolation is split vertically so the image and trisolation can be displayed side by side. You may find that the viewports are too small. It is possible to resize and move the active viewport while in the midst of a point digitise action if you find it necessary to alter the viewport size and/or location. If the two viewports overlap then the viewport in which the point must be digitised is brought to the front when necessary. Finding the registration points It is generally easier to locate the position of registration points in the DTM if the image has been rendered with a Light Source before starting the process of defining the registration points. This is because surface features are much more obvious when rendered with a light source and easier to relate to the image. Memory usage Image files, especially if they are large, can consume a considerable amount of memory. To estimate the memory requirements for displaying an image, use the following formula: image memory usage = X pixels * Y Pixels * 3 bytes Therefore, an image which is 1000 pixels square will require of the order of 2.5 Mb of memory. If you want to see all of the steps performed in this chapter, either run or edit: _10_image_draping.tcl Note: You will need to Apply the forms which are presented.
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DTM / DTM Intersections 1. Upper triangles of 2 DTMs This function takes two DTMs as input and creates a new DTM, which is an upper surface combination of the two input files. We will now look at combining a DTM representing a proposed waste stockpile and a DTM representing the topographical ground profile to produce a new DTM of the ground profile containing the waste stockpile. Open the two DTMs called topo_dump1.dtm and dump1.dtm, appending them both into the same layer. These represent a topographic surface and a dump surface model. From the Surfaces menu, select Clip or intersect DTMs, then Upper triangles of 2 DTMs. The DTM/dtm Upper Results Storage form is displayed. You are prompted for a layer name in which to display the resultant DTM and the object number to assign to this DTM. Enter values of your choice, e.g. combined_surface, object number 1. The layer name cannot be the same as any of the current layers.
Now follow the prompt by picking each of the DTMs. The order of selection is not important. The program will go through the process of joining the two DTMs, finishing with the statement Calculations are completed. You will now be in the layer you specified with the resultant DTM displayed. The result is a DTM of the waste stockpile surface incorporated into the topographic surface.
If you want to see all of the steps performed in this chapter, either run or edit: _11a_upper_triangles_of_2DTMs.tcl Note: You will need to Apply the forms which are presented.
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2. Lower triangles of 2 DTMs This function takes two DTMs as inputs and creates a new DTM, which is a lower surface combination of the two inputs. We will now look at combining a DTM representing a proposed pit design and a DTM representing a topographical ground profile to produce a new DTM of the ground profile containing the pit design. Open the two DTMs called topo1.dtm and pit1.dtm, appending them both into the same layer. These represent a topographic surface and a pit design surface model. Go through exactly the same process as described in the previous exercise except choose Lower triangles of 2 DTMs. The result is a surface representing the pit incorporated into the topography.
If you want to see all of the steps performed in this chapter, either run or edit: _11b_lower_triangles_of_2DTMs.tcl Note: You will need to Apply the forms presented.
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3. Create solid by intersecting 2 DTMs This function takes two DTMs as inputs and creates a 3DM, which is the volume enclosed between the intersection of the two DTMs. We will now look at combining a ground terrain profile with a proposed pit profile to find the volume of material which must be extracted to create the pit. Open the two DTMs called topo1.dtm and pit1.dtm, appending them both into the same layer. These represent a topographic surface and a pit design surface model. From the Surfaces menu, select Clip or intersect DTMs, then Create solid by intersecting 2 DTMs The DTM/dtm Intersect Results Storage form is displayed. You are prompted for a layer name in which to display the resultant DTM and the object number to assign to this DTM.
Enter values of your choice, e.g. layer_intersect, object number 1. The layer name cannot be the same as any of the current layers. Now follow the prompt by picking each of the DTMs. The upper DTM (topography) must be selected first, followed by the lower DTM (pit). The program will go through the process of joining the two DTMs, finishing with the statement Calculations are completed. You will now be in the layer you specified with the resultant 3DM displayed. The result is a solid 3DM representing the material that will have to be removed from the designed pit. The image below shows before and after the DTM/DTM Intersection.
From the Solids menu, select Solids tools menu, then Report volume of solids to create a note file with the volume of the Pit below the topography.
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If you want to see all of the steps performed in this chapter, either run or edit: _11c_create_solid_intersecting_2DTMs.tcl Note: You will need to Apply the forms which are presented.
Summary • • • • •
String file (*.str) contains spatial data A DTM is a digital terrain model which is an indexed list of triangles which contain no spatial data A DTM file is invalid without its associated string file Triangles are referenced in 3-D space by points in strings and the triangles are formed by connecting groups of three data points together by taking their spatial location in the X - Y plane into account. Vertices of triangle coincident with a string point.
Uses: • Surface to surface volumes • Model weathering surfaces, topography • Visualisation • Extract sections and plans Conventions • One DTM surface per file • Breakline v SpotHeight • No vertical or overhanging surfaces
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String file hierarchy
DTM file hierarchy
String Segment Point
Object Trisolation Triangle
Breakline strings are those strings which represent physical features that you can see in the real world e.g. crest of a pit, a fault in a geological model, a contour. No breakline strings should cross over other breakline strings, unless the two strings cross at a common point. The breakline test is an important concept to understand if DTM is to accurately model terrain Spot heights are random points so will triangulate nearest neighbour
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