Site Model Issues

[colby]

I'm having trouble creating a site model from 3d polys. I've learned that using "convert to polygons" can make too many vertices so instead, I traced the topo lines with the polyline tool (so I can control the number of vertices). I've also learned that VW site models cannot have vertical walls or inverted "caves" so I've offset all topo lines a few inches so there are no vertical walls, just a few steep ones. The 3d polys look great (see attached) but when I turn them into a site model, VW randomly changes some of the topo lines.

Please help.

Edited October 17, 2007 by colby

[J Lucas]

Check to see if the answers to my post "2D Polys to 3D Contours" on 10/3/07 are helpful.

[colby]

J Lucas,

Your post helped me get to this point but not beyond. The 3d polys are all set to the correct elevations and the "validate 3d data" command reports no errors but still the site model comes out wrong.

[boxjoint]

Is your site model set to perform contour smoothing, perhaps? (In the create site model dialog box)

[colby]

Boxjoint,

Thanks, that fixed the 2D display...

but when I display the site model in any 3D mode other than 3d extruded contours, I still get these grey zones at flat areas and some strange grey "bridging" at the steep slopes. Thoughts anyone?

[boxjoint]

Colby,

The flat areas could be caused by the combination of the type of rendering you have chosen and the way you are displaying the site model. Try a different combination.

The three stacked grey triangles in your excavation may be the "ground" leaking out from behind the site modifers, depending on how your modifiers are set up.

You may need to check your vertices to be sure you don't have any holes.

I've had these problems too. Frustrating. My fixes are usually workarounds. Perhaps someone with better DTM knowledge can help.

[colby]

Boxjoint,

It seems to happen in all render modes (even final quality renderworks) and in all 3d site model display settings other than 3d extruded contours.

There aren't any holes in the vertices and, after getting a tip that I actually may not have enough vertices, I added some to the topo lines that are giving me trouble and that also didn't fix it. I'm about ready to give up and only display in unsmoothed 2d and extruded contours in 3d. That would be a shame because this tool seems to promise so much.

[boxjoint]

Colby,

As to your excavation, I had a similar problem and solved it by drawing a set of 3d polys around a pad as shown in the attached files. The pad is red and is set to elevation. The 3d poly that surrounds it is offset a small amount, as little as 1/16" as seen in the closeup. I added vertices at the corners, doors, and other key locations and adjusted the z values of each vertex.

Make sure you put the poly in a class called Site-DTM-Modifer. Set it up if it doesn't already exist. This will make the poly act as a site modifer. Essentially what you are doing is creating a plane (between the edge of your pad and the 3d poly) that will describe the inside wall of your excavation.

It made the model work but almost drove me mad.

The flat areas are probably also caused by the model peeking out somehow. I don't get it either but I've had to actually modify elevations slightly to eliminate the problem! How's that for software not getting in your way!

You might try the Drape feature, though I haven't used it so I cannot offer guidance. I believe it will even out slight irregularities in the surface of the model and allow a better render. Let me know how it works if you try it.

I agree that the DTM has great potential, but it is not so easy to work with.

[colby]

Boxjoint,

It turns out the grey "bridging" is the source data poking through (the 3d polys were set to the "none" class with a grey fill). You can get rid of it by changing the class attributes before creating the site model or by unchecking the box that says "keep source data in same layer" but I don't know what the ramifications of doing that are. I'm still new to the program.

Your suggestion of using a pad is a good one, though that may deem the excavation as proposed work, rather than existing like it should be for my particular case. Thanks again.

[colby]

After this ordeal, I wrote this "how to" for our office. Some of you may find it helpful and I welcome any changes/criticism.

Steps to create an existing Digital Terrain Model (DTM) from an AutoCAD survey:

Decide how you are going to make the model and most importantly, what will be ?existing? and what will be ?proposed? when it?s complete. The following steps should be used for the existing site only. Later on you will use site modifiers to change parts of it to ?proposed.?

Import .dwg survey into a new VW file with ACAD layers>VW classes.

Sort through the classes and see if anything is already in 3D that you may be able to use.

If everything is in 2D, carefully trace over the topo lines with the polyline tool, starting from the lowest elevation and working up; if you trace out of order, the 2D contours>3D polys command is more tricky, but not impossible.

When tracing, do not create arcs (do that manually by creating many vertices with the straight line part of the polyline tool) and do not create vertical ?walls? or inverted ?caves?. Avoid this by offsetting the traced topo lines by a small amount (1/2?) to make very steep, but not vertical walls. At no point can the lines touch or cross.

Cut and paste only the newly traced topo lines into a new VW file and put everything on the ?none? class.

Select all and pick ?2D contours>3D polys? command from the AEC menu. Use the tool to change the Z coordinates (elevations) for each of the topo lines.

Select all and use ?validate 3d data? command from the AEC menu. If it reports any errors, use the loci to find the problem and fix it.

Select all and use the ?create site model? command from the AEC menu. Change the settings appropriately and in 2D, make sure the ?smoothed? option is not selected as this can sometimes create problems. Also experiment with the ?keep source data in the same layer? checkbox. If you leave it checked, make sure the class attributes of the 3D polys have no fill.

[Guest]

1. Keep the data on a separate layer (and/or class) than the site model.

The solid fill of the polygons (source data) is what's popping up through the side model.

Either adjust the solid fill, or set the class/layer with the source data to be invisible.

2. Check the site model properties (graphics) and set whatever is gray to some other color

3. Rather than trace over the source data with a polygon to reduce the number of vertices, use the Filter 3D Polygons to reduce the number of vertices in each polygon.

[jbrhwy]

Get the actual survey data from the surveyor, which will be in the form of point data, not the converted "AutoCAD survey". This will save a lot of time & potential mistakes.

There are numerous previous postings on this.