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Terrain Model Precision

I will I

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Is there any setting or best practices to increase the precision of the terrain model when generating from source contours, the slope analysis I am trying to do is misrepresenting large areas of our site?

When comparing the source contours with the ones generated in the terrain model it is apparent that large areas of the generated contours are looping back on themselves simplifying them far too much when compared to the originals.

I have attached a screenshot showing the issue, generated contours are shown in red. I am not asking for perfect reproduction but this site is quite large, some of these areas where the contour is looping back on itself are almost 100'/30m apart.


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I will I - Set your Site Model to triangles to see what's happening. When this happens to me, it's usually because the vertices on a contour are connecting to other vertices on the same contour instead of to the next contour up or down. I call it bridging. Probably same as your looping. Adding vertices to the existing contours doesn't usually help.

My fix is to add some "encouragement" for the site model to connect between the contours. I add a few 3d loci or 3d Polys placed in plan projection about half way between the bridged or looped contours and raised to z height half way between the z values of the orig contours. Right click the DTM (the site model) and choose Edit Site Model Source Data. This will display the contours. Make sure it's showing top/plan view. Add additional 3d loci or 3d polys at xyz half way between the original source contours. Sometimes even more loci are needed at intermediate z values (eg if the contours change z=10' and placing a locus at z+5' doesn't complete the job, you might need loci at the z+2', z+4', z+6, etc.

Maybe your model can be corrected with just a few loci, eg one or two at each failed location.

Another drastic thing to try is to remake the DTM from loci. Use the Duplicate Along Path command to make a bunch of 3d loci along each contour, say at 12" separation. Select these loci to create the terrain. They can be colored and classed during creation to allow selection and visual differentiation.

Post back if things aren't working.



Edited by Benson Shaw
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This is an issue I have been battling with for a while. I usually create the site model with 3D polys traced over the original survey and have used the methods Benson suggested to nudge the model into position.

I have been pestering a couple folks at VW to have this issue fixed and wish that would get stepped up in the priority list. It just seems to me that if I put a 3D poly in a certain spot that the generated model could keep that elevation in the same place as the source data. Just sayin'.

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