Tuesday, 28 May 2013

Create Profile for Watermain

This comes up that often that I'm surprised there isn't a command in Civil 3D to do this for you.
The issue is that for a watermain survey you may typically have only a single line of GPS points surveyed. How do you create a profile of the pipe route in Civil 3D? Well that is easy, of course it is, there is a create profile from file option in Civil 3D that will do it for me. Not so fast... the point file you have from your GPS logger will probably be in the format PENZ (point number, easting, northing, elevation). The create profile from file command requires a .txt file with two sets of values - chainage and elevation separated by spaces. To convert typical GPS survey points from coordinates into chainage is a long winded process but is possible using Civil 3D and Excel.
There is an Alternative
If you create a surface from the single line of points it will not triangulate properly and you wont be able to pull a sensible looking profile along the entire pipe route. As a way of getting around this you can create dummy levels to allow you to create a proper surface and then create your profile along the route. You can do this by joining the points using a featureline and then offset this line left and right by a nominal amount, then create a surface from them. The steps are as follows (there is a video at the bottom with me narrating, Morgan Freeman wasn't available):
  1. Import your points into Civil 3D.
  2. Join the points using a 2D polyline (a quick tip here is to use the transparent commands. When you start the polyline command and it asks you for the first point type 'PN and press enter and then type the point numbers you wish to draw the lines between. eg to join between point 1 & 100 type 1-100 and press enter. This will join up the points in one quick step).
  3. Use the create alignment from object command and select the polyline to create an alignment along the pipe route - we need this to create our profile.
  4. Repeat step 2 except create a 3D polyline using the 3DPOLY command. You can use the quick tip again.
  5. Use the Create Featureline from Objects command to create a featureline from the 3D Polyline. Untick the box to assign elevations when the create featurelines dialog appears.
  6. Select the Featureline after you have it created and click on Edit Geometry on the ribbon. Click on the button for Stepped Offset and enter 1mm for the offset distance, select the offset side and enter zero for the level difference. Repeat for the other side.
  7. Select the 3 featurelines and choose Add to Surface as Breakline on the ribbon. Create a surface if not already done so and accept the defaults.
  8. Select your alignment created in Step 3 and choose Surface Profile on the ribbon. You should now see your surface  and be able to create a profile as usual.
There is a video of the workflow at the following link:

For anyone who might be interested in doing this using the other method mentioned above, the workflow to convert point coordinates to chainage is as follows:
  1. Follow steps 1 to 5 above.
  2. Select the featureline and click on Edit Levels on the ribbon. Open the Elevation Editor and right click on the values and select Copy All:
  3. Paste the values to excel and delete the columns you don't need (we only need chainage and level columns)
  4. Save as a csv file and open in Notepad. Use the Replace command (under Edit menu) to replace all the commas with a space. Save as .txt file.
  5. In Civil 3D use the Create Profile from File command and select the txt file and this will give you the profile.

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