Tech Tips


Triangulation Methods

This Tech Tip explains the 2 options available when triangulating a terrain file (dtm).
 

TechTips

Introduction

In Civil Designer 2014 and later versions, there are 2 methods available when triangulating: In-Memory, and On-Disk.

In-Memory

This method triangulates a terrain surface using normal memory. It is therefore faster than the on-disk option but might be limited by the available memory on your system.

The Triangulate routine creates triangles using break lines only and all pre-existing break line data on that surface is deleted before processing begins. Feature line data, however, will be retained.

This form of model creation uses a Constrained Delauney tessellation algorithm to form the most equal-angular triangles that are possible (with due regard for any feature lines already present on the surface) and then converts these data to lines.

Note: This function is very susceptible to failure if your model has duplicate points and you should run the Remove Duplicates function before triangulating the site.

Terrain Mode > Model Menu > Triangulate > In-Memory



Select the surface you want to triangulate, click on the drop down to change the surface. Specify the maximum line length, this should be greater than the largest distance between your survey points. Doing a graphical join will allow you to measure the distance (Terrain Mode > Graphical Menu > Join). If you select "No length check" then the program will attempt to join all the points no matter the distance apart.

Click OK to continue.



Once the triangulation is complete, information about the triangulation will be displayed. Click OK to continue.

If there is a problem detected during the triangulation then the function is automatically cancelled and you are presented with an error message.



This hints at what are the most likely reasons for the triangulation failing: i.e. duplicate points or crossing feature lines.

On-Disk

This method triangulates a terrain surface using paged memory on disk. It is therefore slower than the in-memory option but will handle far larger models.

The Triangulate routine creates triangles using break lines only and all pre-existing break line data on that surface is deleted before processing begins. Feature line data, however, will be retained.

This form of model creation uses a Constrained Delauney tessellation algorithm to form the most equal-angular triangles that are possible (with due regard for any feature lines already present on the surface) and then converts these data to lines.

Note: This function is very susceptible to failure if your model has duplicate points and you should run the Remove Duplicates function before triangulating the site.

Terrain Mode > Model Menu > Triangulate > On-Disk



Select the surface you want to triangulate, click on the drop down to change the surface. Specify the maximum line length, this should be greater than the largest distance between your survey points. Doing a graphical join will allow you to measure the distance (Terrain Mode > Graphical Menu > Join). If you select "No length check" then the program will attempt to join all the points no matter the distance apart.

Single pass: Select this option if there are no feature lines on the surface being processed or if you are certain that no crossing feature lines exist. This is faster than the following option as only a single pass through the database is required as both points and feature lines are added to the triangulation simultaneously.
Two passes: Select this option only if there are feature lines on the surface being processed AND you are unsure if any crossing feature lines exist. This option is slower than the previous option as two passes through the database are required, the first pass processing only existing feature lines (in order to determine if any crossings exist) and the second pass processing only points not connected to any feature lines.


Click OK to continue.



Once the triangulation is complete, information about the triangulation will be displayed. Click OK to continue. (notice the difference in speed, the same dtm was used)

If there is a problem detected during the triangulation then the function is automatically cancelled and you are presented with an error message.



This hints at what are the most likely reasons for the triangulation failing: i.e. duplicate points or crossing feature lines.


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