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CyberAngel
9th Aug 2007, 01:59 pm
A co-worker has a strange problem. We use LDD 2006. He built a surface from contours, created an alignment for a sewer line, sampled the existing surface, and drew a profile. The surface that appeared on the profile doesn't match the elevations of the contours, e.g. at station 0+00 the surface is 328.4 and the profile is 334.3. I thought it might be a simple offset, but the difference at the opposite end is about 2 feet off instead of about 6 feet.

Some things we know are not the problem. There's only one alignment in the drawing, so it's not a case of using the wrong alignment. There are only two surfaces, existing and proposed, and the proposed surface doesn't extend to the area where the alignment starts. The Terrain Model Explorer says that the minimum elevation of the existing surface is at 328.4. It's almost like the profile generator is reading surface data from a different project, but the project path in the title bar matches the drawing path. Anybody have any ideas?

CyberAngel
9th Aug 2007, 03:14 pm
After a lot of head-scratching, we found the problem. The existing site plan was xrefed into the grading plan, but at a slightly different location. It was close enough for the alignment to fall inside the existing surface, but the elevations were all wrong. We moved everything in the grading plan to match the existing site plan, redefined the alignment and the proposed surface, and got everything to match up.

Now, if somebody has the same problem, here's a possible solution.

rustysilo
10th Aug 2007, 02:34 pm
Did you produce contours from the surface after creating it to ensure they match the existing contours on your plan? Using contour data alone can sometimes give you undesired results.

CyberAngel
13th Aug 2007, 01:24 pm
Normally, if we suspect that kind of problem, we use the Quick Display command on the Terrain Menu. That's how we tracked down this particular problem--the surface was obviously not matching up with the contours in the grading plan. If the error were much smaller, though, creating another set of contours would help. Thanks!