Classify DTM Triangles

You can use this function to classify triangles in a DTM using a number of closed boundary segments, and the description field of the classifying segment. The value for this description field is assigned to a description field of the triangles in the DTM.

To run this function: Choose Surfaces > DTM file functions > Classify DTM triangles, or...

• In the Function Chooser, type CLASSIFY DTM TRIANGLES, and press ENTER.

This function splits triangles that cross the boundary segment and creates new triangles. Creating new triangles preserves the geometry of the surface and ensures that no triangle crosses a boundary segment.

You can use CLASSIFY DTM TRIANGLES with the DRAW DTM/3DM function to draw a DTM with different colours for different triangles. Using the values assigned to the triangle description fields to control the DTM colour provides an effective 3D GIS feature.

Fields on the Classify DTM triangles using boundary segments form

Field	Description
Define the DTM to be classified
Location	The name and location of the DTM you want to classify.
Object ID	The object number for the DTM.
Trisolation ID	The trisolation number for the DTM.
Define the boundary strings
Location	The name and location of the boundary string file to use to classify the DTM.
ID	The ID number of the boundary string file.
String range	The strings that you want to use to classify the DTM. The boundary string can consist of any number of nested segments. The direction of these segments (clockwise or anticlockwise) is not important Imagine that you are viewing a surface along the normal to the plane used during surface creation (that is, looking directly at the plane), the rules for clipping are: For a single segment string, "inside" the segment refers to triangles physically inside the segment. For a string with a single level of nested segments, "inside" refers to triangles physically inside the outermost segment but outside any inner segments. Multiple levels of nesting are handled by alternating "inside" and "outside" for each level of nesting. For example, if the black lines are segments of a string, the red areas are considered "inside" the string and the white areas are "outside":
Classifying field	The field of the strings in the string range that you want to use to classify the DTM.
Default classification	The classification value that you want to use for the DTM. This value is usd if there is no value in the classifying field of the boundary strings, and for triangles outside the boundary strings.
Define the DTM file to be created
Location	The name and location of the file in which you want to save the classified DTM.
ID	The ID number of the new DTM file.
Description field	The description field of the triangles in the new DTM that is assigned the value from the classifying field of the boundary strings.

Output

A new DTM that is geometrically identical to the original DTM is created. Calculation of volumes, contours, cross sections, and other features all produce the same results. However, contours and cross sections can contain additional points caused by the creation of additional triangles.

You can apply this function to the DTM you have just created, with a different set of classifying segments, to assign further classifications to different triangle description fields. If the description fields are not reused, any existing classifications to the triangle description fields are preserved. This means you can perform multiple classification passes. For example, you can:

• classify triangles by rock type
• classify triangles by mining lease boundary
• classify triangles by any other characteristic of interest

Troubleshooting

Message	Description
Triangle with zero area created Data point geometry is causing problems in DTM Look in string X segment X offset X for the problem	During processing, some of the triangles split at the boundary line have formed new triangles with close to zero area. This is a warning message only, and processing will continue. Please report this error, with appropriate data, to your local GEOVIA support centre for investigation.