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.
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.
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.
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
String file hierarchy DTM file hierarchy
String Object
Segment Trisolation
Point 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