DTM

[Jean-Marc]

I am new to DTMs (v.10) and trying to get a grasp of the processor?s capabilities and limitations.

I hope to generate a DTM for a project that will involve extensive earth sculpting and a large volume of imported soils. My primary concern in generating the DTM is to determine the amount of fill that will be required. Most of these earthworks are unrelated to any other site modifications such as roads, pads, or walls. Consequently, if I understand the User?s Guide correctly, none of the site modifiers can be used to create the topography I need. Is it possible for me to simply manually edit/add/delete contours in my proposed DTM symbol? I?ve tried this once on a DTM, and it would appear that I corrupted the model.

If I cannot edit the DTM, is it possible for me to generate a new ?existing? DTM derived from my proposed contours, and then process the fill calculations by comparing the two ?existing? DTMs?

Thanks.

[Robert Anderson]

Certainly this is possible. You should use the Site modifier object in the form of "Pads" to describe the new shapes you want. Surround your ares of "Pad" modifications with a "Fence" and you should be able to get a cut-and-fill calculation.

[Jean-Marc]

The problem with pads is that they are planar objects. These can only generate flat (and sloped) surfaces, and are fine to render grading plans around, say, a patio or raised terrace. But what if, as I indicated in my question, I want to create undulating, curvilinear topography and organic landforms that are not related to any particular built surface or structure.

I can easily draw a 2d contour plan to depict the topo that I want. Is there any way to convert this 2d plan into 3d polys that can somehow then be used to redraw the contours in my "proposed" DTM, so that I can calculate the cut and fill?

[Robert Anderson]

You can use a NURBS surface as a site modifier:

1. Create a NURBS surface in the form you want.

2. Use the Convert to 3D Polys command to convert it to triangular 3D polys;

3. Set the 3D Polys to the Site-DTM-Modifier class.

4. I recommend that you place a fence around the outside of the NURBS in plan view.

5. Run Site Model.

[Jean-Marc]

Thanks Robert, I'll give this a try.