How to combine / merge surface with overlapping data
Step by step
1. On the Civil 3D Toolspace, click on "Prospector" tab.
2. Right mouse click on "Surfaces" and create a new surface.
3. Expand the "Definition" subfeature for that new surface and right click on "Edits".
4. Click "Paste Surface" and chose the original surface.
5. Change the new surfaces style to show points.
6. Create an outline of the area you wish to overwrite with you updated surface data.
7. Once outline is drawn, navigate to the new surfaces definitions and click on the "Edits" feature again.
8. Click "Delete Point", and select all the point visible within the outlined area.
9. Once all the points in the outlined area have been deleted, click on the "Edits" feature one more time.
10. Click "Paste Surface" and chose the updated data surface.
11. Change the new surface style to show contours or desired look
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