Intersect solids

The debug files "consolidation_triangles1.str" and "bad_triangle1.str"

If CONSOLIDATION occurs during the triangle intersection process, Surpac attempts to fix the problem automatically by moving a triangle vertex by a small amount (at most at a third decimal place level). Once CONSOLIDATION has occurred the triangle intersection process restarts. In general CONSOLIDATION is caused by one of the following circumstances:

• a vertex of a triangle in one of the trisolations is very close to a vertex of a triangle of the other trisolation;
• a vertex of a triangle in one of the trisolations is very close to an edge of a triangle of the other trisolation;
• a vertex of a triangle in one of the trisolations is very close to a face of a triangle of the other trisolation;
• an edge of a triangle in one of the trisolations is very close to an edge of a triangle of the other trisolation.
• an edge of a triangle in one of the trisolations is very close to a face of a triangle of the other trisolation.

In general, Surpac can automatically resolve any CONSOLIDATION problems that occur. But sometimes the maximum number of CONSOLIDATIONS of 50 is reached and the intersection function exits, or some later problem occurs. In this case the file consolidation_triangles1.str can be very useful in helping you to resolve the problems manually.

If any CONSOLIDATIONS occur, Surpac creates and outputs the file consolidation_triangles1.str whether or not it has managed to automatically resolve the problems. If the intersection function exits with an error, you are informed about the file with an error message box, if the function completes correctly you are informed about the file with an information message.

Surpac can also create a second debug string file bad_triangle1.str. This file is generally created when Surpac has managed to automatically resolve all the CONSOLIDATION problems, but has found another triangle that is causing problems later on in the calculations. The vertices of this single triangle are written to the file bad_triangle1.str. The triangle may come from either of the two selected trisolations.

It is advised that you use the following steps to use the debug string files consolidation_triangles1.str and bad_triangle1.str to manually alter the input trisolations to correct problems in the intersection functions:

1. If the file bad_triangle1.str has been created use this file first, otherwise use consolidation_triangles1.str
2. Use the EXIT GRAPHICS function to clear the graphics screen of data
3. Recall the debug string file into graphics (you will find you get better visualisation if you pull this file in first)
4. Recall one of the original .dtm files into graphics (in general its better to choose the smaller, less complex of the two solids). Make sure you recall the .dtm file into a separate layer. You should now see the .dtm file and the debug string file both displayed. Type HIDE ON (to enhance the display) and rotate the image to get the best view. Note: In general you should only have to edit one of the trisolations in this way, however in certain situations you might find it easier to edit both of the trisolations to achieve the desired outcome.
5. Use View->Layer->Properties to make sure that the .dtm layer is the active layer, and that the debug string file layer is 'not selectable'.
6. By looking at how the triangles in the debug string file intersect with the triangles in the .dtm file you should be able to see how all the CONSOLIDATIONS occurred, and which of the vertices in the .dtm file must be manually moved to correct each problem. Try toggling EDGES ON/EDGES OFF and FACES ON/FACES OFF to get a better view of the triangles in the debug string file.
7. What you now have to do is WINDOW IN on each of the particular problem areas and use the function POINT MOVE to move an appropriate vertex in the .dtm layer by a small amount to resolve the CONSOLIDATION problem (this will typically involve pulling one vertex in the .dtm layer slightly away from a vertex or an edge or a face in the debug string file layer). What is a correct 'small amount' will vary from case to case, but in general you should only need to move a vertex by 0.05 to 0.15 to resolve the problem (if accuracy is very important try 0.001 to 0.005, it should still work). If you have a choice, it is best pick a vertex which is as close as possible to the point that is causing the CONSOLIDATION. Keep going round the solid moving vertices for each CONSOLIDATION problem until you have dealt with them all. Note: you should usually only have to move one vertex to resolve each CONSOLIDATION problem. Hint: The more you use WINDOW IN to window in on an area, the more control you'll find you have over using POINT MOVE to move a vertex by a small amount. Hint: To change the point of rotation for viewing use View->Viewing options->Select camera target, you will find this extremely useful for improving the viewing rotation after you have done a WINDOW IN.
8. When you've moved all the vertices, you will have to revalidate the solid (use function Solids->Validation->Validate trisolation), and set the direction (use Solids->Validation->Set trisolation to solid or void). Note: If the trisolation is a true DTM surface (ie it was created by the CREATE DTM function) then you do not have to revalidate it or set the direction, just ensure that you do not move the point so as to cause a self intersection or fold-back in the DTM. Save the solid to a .dtm file (either to a new file or overwrite the existing file, as you prefer). Then you can perform the intersection function again with the new data.
9. Note: If Surpac created a bad_triangle1.str then you should only have to resolve the problems in this file. The fact that Surpac got this far means that it was probably able to automatically resolve the problems in consolidation_triangles1.str. This may not be the case however, and you might find you also have to resolve the problems in consolidation_triangles1.str too before the intersection will work.