When attempting to import a DXF file in Terrain Extractor (Trex) to assign elevations, the following error occurs:
"The data source file must contain at least three unclipped points in order to create an elevation map"
This message indicates that Terrain Extractor did not find any supported elevations in the data source that overlapped model elements. Here are a few possible reasons and solutions:
First, check to make sure that the selected X-Y units in the Trex wizard are correct. To see the X-Y unit of the model, go to File > Options > Units and check the unit next to "Coordinate".
If the correct units are chosen, the model may be in a different coordinate system / spatial reference. Try adding the DXF as a background layer (again choosing the right units) and click the Zoom Extents button to see where the file is in relation to the model. If the drawing pane appears blank when using zoom extents, it may mean that the model is very far from the DXF file (requiring it to zoom out so far that you cannot see anything). Try pressing CTRL+A in this case to select all elements - you should see a red area where the model is, and the data source may be in the opposite corner.
You can also open the data source file in another application (such as MicroStation or AutoCAD) to check the units and compare to the units of one of the model node elements. For example open the properties of a junction and look at the X and Y field at the top, or hover your mouse within the model and look at the X and Y shown at the bottom-right corner of the program.
If the DXF is in a different coordinate system than the model, then you may need to reproject the model, or for a quick check you could try selecting the entire model and drag/drop it on top of the background layer. (after adding the DXF as a background)
If the DXF file with the elevation data is spatially aligned with the model, this issue could be due to the type of information in the DXF. For example if the elevation values are assigned to circle entities in the DXF that look like points, Trex will see them as polygons, so the DXF point and DXF contour data source types will not be able to recognize the elevations. In this case you will need to convert the circle entities to point entities first.
If in doubt, open the DXF in MicroStation or AutoCAD and check the entity type of the features that contain the Elevation information.
If you have lines in a DXF that contain the elevation information, you may need to use the "DXF Contours" data source type in Trex. In this case, it should be able to pick up on the elevation from the line closest to each model node element, but this will not be the same as having actual contour polylines. Be sure to examine the file in its native application to check if all of your elevation data is stored in the line elements.
Using Terrain Extractor (Trex)