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About DTMs
DTM stands for digital terrain model. In SimuTerra there is a concept of a DTM set, which always has an Existing DTM. In SimuTerra Pro, this set may also include a Proposed DTM, and, if so, it may also include a Cut and Fill DTM.
A Proposed DTM starts with the Existing DTM, and alters it with whatever modifying data belongs to the DTM such as roads and pads. A Cut and Fill DTM represents the difference between the Existing and the Proposed.
A DTM is calculated by the TIN method, or Triangulated Irregular Network. It uses all data which you give it, without making any approximations. Polys (such as those representing imported contour lines) contain information in their vertices, and also force linear interpolation along their lengths, so they can be used as breaklines.
A DTM has various parameters which can be changed in the Info Panel.
The value labeled "Max. grid squares" is the maximum number of squares to be formed if you choose to display a square grid in 3D views. The grid is draped over the DTM. If the DTM is square, with edges parallel to the x and y axes, then you may end up with this number of squares. If the DTM is triangular, you may get half this number. There is no way to set the specific width of each square. The direction of the edges of the grid squares is always parallel to the principal axes.
The Existing DTM always exists within a DTM set. With SimuTerra Pro you can also create the other kinds of DTMs. If the Proposed DTM doesn't exist, you can create it by clicking on the Proposed checkbox. Likewise, if the Cut and Fill DTM doesn't exist, you can create it by clicking on the Cut and Fill checkbox
There are three columns of controls, one for each kind of DTM within a DTM set. For each of these three columns, there are two columns of checkboxes and one column of color wells.
Cont. Intvl.: Contour interval. The difference in elevation between contour lines. This must be a positive value.
Index Mult.: Index multiple. An index contour is drawn for every nth contour line, where n is the index multiple. An index contour is drawn thicker than the other contour lines. If you choose to display contour labels, they are drawn along index contours. This must be a positive integer. If you set it to 1, then every contour line will be an index contour.
Min. Elev.: Minimum elevation. This is the lowest elevation for which contours will be drawn. If you set it higher than the highest point or vertex in the DTM, then no contours will be drawn. This value cannot exceed the one which you enter for maximum elevation.
Max. Elev.: Maximum elevation. This is the highest elevation for which contours will be drawn. If you set it lower than the lowest point or vertex in the DTM, then no contours will be drawn. This value is not allowed to be less than the one which you enter for minimum elevation.
Base Elev.: Base elevation. This is usually zero. Its purpose is to offset the contours. For instance, if the contour interval is 2, and you set the base elevation to 1, then you will get contours at 1, 3, 5, etc. This can be set to any value.
Datum Elev.: Datum elevation. This elevation is used for calculating cut and fill volumes within one DTM kind. For instance, within an Existing DTM, the cut volume is the volume which would need to be cut to get from the existing DTM to the datum elevation. In a Cut and Fill DTM this value should typically be set to zero.
Contours: Whether to show the contours in 2D views; whether to show them in 3D views; what color to use.
Labels/Grid: Whether to show contour labels in 2D views; whether to show a square grid in 3D views; what color to use for the grid.
Triangles: Whether to show triangles in 2D views; whether to them in 3D views; what color to use for them.
Hull/Texture: Whether to show the hull (outer edge) in 2D views; whether to use textures in 3D views; what color to use for the hull.
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