Create DTM from layer

You can use this function to create a DTM from the data you have loaded in the active layer in Graphics.

To run this function: Choose Surfaces > Create DTM from layer, or...

In the Function Chooser, type GRAPHICS CREATE DTM, and press ENTER.

Fields on the Create a DTM From a Layer form

Field	Description
Object ID	The ID for the object in the new DTM.
Object Name	The name for the new DTM.
Projection plane
Create on:	The plane the DTM is created on. You can choose: The XY plane: Uses global coordinates. This plane is usually used for topographic data. The active plane: Uses the viewing plane that is currently active in Graphics. Note: This option is not available if the active plane is the XY plane. The best-fit plane: Uses the coordinates of the plane that best fits the data in the string file or layer. Note: If you select the best-fit plane, the After creating the surface, change the current plane to the best-fit plane check box becomes active.
After creating the surface, change the current plane to the best-fit plane	Selected: The current plane is changed to the best-fit plane after the DTM is created. Cleared: The best-fit plane remains temporary after the DTM is created.
Creating a DTM using breakline test
Perform break line test	Selected: Test if break lines intersect. DTMs are created only if break lines do not intersect. Cleared: Do not perform the break line test. Recommended only if you know break lines definitely do not intersect.
Interpolate additional points	Selected: Interpolate additional points before creating the surface. You might want to select this check box when the strings have long straight segments with few points, for example, strings that are generated during pit design. Cleared: Do not interpolate additional points.
Point interpolation distance	If Interpolate additional points is selected, the distance at which new points are created.

Output

A DTM is created in the active layer in Graphics. If crossing breaklines are identified, they are marked with red temporary markers at an elevation above the data in the active layer. The markers make it easy for you to see where the crossing breaklines are located.

Tip: You can run the breakline test manually using the CLEAN LAYER function.

Troubleshooting

Message Description

Message	Description
`POINT nn WITH RL xx HAS SAME X,Y AS POINT ii WITH RL yy NOT FATAL`	Points with the same X, Y coordinates and different Z coordinates will be replaced with one point, the Z coordinate being the mean value.
`Triangle not found for point` `String xxx segment xxx point offset xxx` `No triangle point is common with the breakline` `String xxx segment xxx point offset xxx`	These error messages indicate an error occured during the creation of the surface where the geometric arrangement of strings, segments, and points is such that it is not possible to create a surface. Note: The string and segment reported in the error message are not necessarily the cause of the problem. However, they do indicate the general spatial location where the problem occurs.
`Error applying breakline to triangles. See warning messages for details.`	A problem has occurred when adding a break line to the DTM surface. The warning messages indicate the location of the problem.

POINT nn WITH RL xx HAS SAME X,Y AS POINT ii WITH RL yy NOT FATAL

Points with the same X, Y coordinates and different Z coordinates will be replaced with one point, the Z coordinate being the mean value.

Triangle not found for point

String xxx segment xxx point offset xxx

No triangle point is common with the breakline

String xxx segment xxx point offset xxx

These error messages indicate an error occured during the creation of the surface where the geometric arrangement of strings, segments, and points is such that it is not possible to create a surface.

Note: The string and segment reported in the error message are not necessarily the cause of the problem. However, they do indicate the general spatial location where the problem occurs.

Error applying breakline to triangles. See warning messages for details. A problem has occurred when adding a break line to the DTM surface. The warning messages indicate the location of the problem.

Errors

Error	Description	Solution

Distance from P1 to P2 is hundreds of units, for example 200 m. The distance between each of the 5 parallel lines is in single units, for example 5 m	String geometry of this type is generally created by the Pit design module. The special feature here is that there are concentric strings, which have relatively large distances between consecutive points on the string and relatively short distances between the strings.	Create points at more regular intervals along the strings so that the ratio of distance between points on a string to the distance between the strings is not so extreme. In the case of pit design data, make the points at more regular intervals in the base string before commencing the pit design.

Offset of Point P1 from the line going from P2 to P3 is very small - a few centimetres.	A point on one line comes very close to intersecting another line but does not actually meet it.	Move P1 to be either exactly on the line P2-P3 or move it further from the line P2-P3.

Distance between P1 to P2 and P3 to P4 is very small - a few centimetres.	A point on one line comes very close to intersecting another line but does not actually meet it.	Move the points so that they are exactly the same in X, Y, and Z, or move them further apart.
`Strings xxx and xxx intersect at xxxxxxN xxxxxE` `xxx Breakline intersections found ........ Cannot form the DTM` `String file failed the break line intersection test`	These error messages appear only if some of the strings are being used as breaklines and the breakline intersection test is being performed. These messages indicate that an intersection has been found between two strings that are being used as breaklines. The string numbers and coordinates at which the intersections have been found are displayed so that you can determine the source of the problem and fix it.	There are two ways to fix this problem. Treat one of the strings as a spot height string. Edit the string file in Graphics and move the locations of some of the points to prevent the intersections occurring.
`Incorrect number of triangles formed` `Triangle array is scrambled` `Fatal DTM error - Triangles are not adjacent` `Triangle stack underflow` `Triangle list overflow` `Searched full circle and can't find a neighbour`	These error messages indicate that a severe error condition has been found during the creation of the DTM.	If you encounter any of these messages contact GEOVIA Support.