Expand DTM

You can use this function to expand a DTM to a new boundary. The new boundary must be a closed clockwise segment.

To run this function: Choose Surfaces > Advanced options > Extend surface to boundary, or...

In the Function Chooser, type EXPAND DTM, and press ENTER.

Fields on the Expand a DTM to a new boundary form

Field	Description
Input DTM
Location	The name and location of the DTM you want to expand.
[Refresh]	Loads the Object ID and Trisolation ID drop-down lists with the objects and trisolations of the DTM. In Surpac 6.6.1 and earlier versions, when you selected a DTM in the Location field, Surpac would load the DTM, validate it, and then load the Object ID and Trisolation ID drop-down lists. You could not interact with the form until the process was complete, which could be a long time for some large DTMs. Now, Surpac does not load the drop-down lists until you click the Refresh button, and validation does not occur until you click Apply in the form. Any validation errors are reported in the Message window.
ID number	The ID number of the DTM you want to expand.
Object ID	The object number of the DTM you want to expand. You can type the Object ID or select it from the drop-down list, if the list is loaded.
Trisolation ID	The trisolation number of the DTM you want to expand.
Expand to boundary string
Location	The name and location of the boundary string file.
ID number	The ID number of the boundary string file.
String No.	The string number of the boundary string.
Segment No.	The segment number of the boundary string.
Breakline properties
Strings to act as break lines	Selected: Strings in the original DTM act as break lines in the new DTM. Cleared: Points in the original DTM are treated as spot heights in the new DTM.
Any spot height strings	Selected: A range of strings in the original DTM are used as spot heights in the new DTM. Cleared: No points are used as spot heights for the new DTM.
Spot height string range	The range of strings in the original DTM whose points will be treated as spot heights in the new DTM.
Expansion method
Boundary dip	The dips at the points on the old DTM boundary are estimated by using a weighted average of the dips of the triangles attached to the point. If there is a lot of local fluctuation of dip at the old boundary, you might find that this creates a "saw-toothed" effect at the new boundary. If you choose Boundary dip, you also enter a Smooth factor. The Smooth Factor can be any integer between 0 and 50. The Smooth Factor identifies the number of points on each side of the point being expanded. The points are then averaged to determine the dip for the expanded point. For example, if the Smooth Factor is 5, five points on either side of the point on the old boundary are used in the averaging, as well as the point itself.
Fixed dip	The dip is defined as a fixed value with a fixed bearing. The dips at the old boundary points are calculated relative to this fixed dip (that is, an apparent dip is used). If you choose Fixed dip, you also enter a Bearing and Dip. The bearing is an integer between 0 and 360, measured in degrees clockwise relative to the positive Y axis. The Dip is the fixed dip value in the range -89.1 to 89.1. For example, if you define a Dip of 30 degrees on a Bearing of 180 degrees, points on the old boundary whose extension lines have a bearing of 180 degrees will have a dip of 30 degrees. And points whose extension lines have a bearing of 0 degrees will have a dip of -30 degrees.
Slope strings	The D1 description field of the slope string segment at the point defines the dip. The slope string is searched for the segment that the point of the old boundary string is contained within, and then uses the value in the D1 field of the first point of the segment for the dip. If a point is inside two or more segments, the segment with the lowest string number is used, or if the segments are in the same string, the lowest segment number is used.. Note: The dips in the D1 fields of the slope strings file must be in the range -89.1 to 89.1 degrees. If you choose Slope strings, you also enter the Location and ID number for the slope string file.
Plane fit	The Plane Fit method extends the DTM to the new boundary using the plane of best fit of the data in the DTM. You will find that the Plane Fit method is the most appropriate for expanding data that lies approximately in a plane.
Output DTM
Location	The name and location for the new DTM.
ID number	The ID number for the new DTM.
Object ID	The object number for the new DTM.
Object name	The object name for the new DTM.

Output

When expanding a surface created on a non-horizontal plane, the process is:

The surface and boundary string are transformed so that the surface plane is horizontal.
The command proceeds as for a horizontal plane surface.
The results are back-transformed so that the plane sits in its original position.

The expanded DTM is created and stored in the defined output .dtm file.

Troubleshooting

Message	Description
`The defined boundary segment cannot be found in the string file`	Check that the new boundary does exist in the defined file.
`The boundary segment is open, the new boundary must be closed`	Check that the new boundary is closed.
`Duplicate points have been found in the boundary segment (search distance = 0.05)`	Filter duplicate points from the new boundary and re-apply the function.
`The new boundary must be outside the old boundary`	Make sure that there is no region of overlap between the boundary of the old DTM and the new boundary segment that you have defined.
`String aa Segment bb of the slope strings file is open, all segments must be closed`	Check that all the segments in the slope strings file are closed.
`Invalid D1 field in String aa Segment bb of the slope strings file`	Check the validity of the dips you have defined in the D1 fields of the slope strings segments.
`A point dip cannot be found because the point lies outside all the segments in the slope strings file`	Make sure that all the points on the boundary of the old DTM lie inside at least one of the segments defined in the slope strings file.