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Discontinuous Contours Terrain Model


JSiegel

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Hi All,

I just received a .dwg survey that I have imported into VW2009. It is a hilly site w/many retaining walls/structures that the contours die into. It is not possible to use the AEC>Survey Input>2D Polys to 3D Contours command as the contours as drawn by the site engineer were not drawn in ascending or descending manner as explained in the VW Tutorial manual.

I am trying to avoid retracing the existing contours from low to high & this still doesn't resolve how to deal with the contour interruptions. Any thoughts on how to deal with creating the terrain model & the contour discontinuity would be helpful.

Thanks,

Jeremy

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There are a couple ways to do this, and others will no doubt have a more sophisticated approach, but the way I would handle it is as follows:

Create a new VW's file. Import the dwg file into it. Create a new design layer, then, starting with the lowest contour line, copy & paste-in-place from the original layer to the new layer. Try, if you can, to make each poly continuous as you go, by connecting the dots and then using the "Compose" command, or if necessary retracing that entire poly. Also, VW's cannot handle any overlapping or doubled back contours. So in cases where the contours all seem to pile up on top of each other (for example, at a retaining wall) you will need to manually adjust them so that they are very close to, but not touching each other. For practical purposes I generally assume that the retaining wall itself will be thick enough to cover these portions of the Site Model. I usually draw the wall(s) in first, at least as rectangles or poly's, so that I can see how much room I have to pile up these contours.

Once you have pasted and made continuous all of the poly's, select them all and run the Modify>Convert>Convert to polygons command. This will convert any existing polylines to polygons. Then with all the contours still selected, go through the normal process of "2d Poly's to 3d Contours". Remember that all this command is doing is making each 2d polygon into a 3d polygon and assigning a "Z" value to each one. The "Z" value can be adjusted later, if needed" simply by selecting the poly and changing the "Z" number in the OIP.

The next step, before actually creating the Site Model is to run the AEC>Terrain>Simplify 3d Polygons command. This is essential to reduce vertices and give you a workable Site Model in the end. You will need to decide what a reasonable margin of error is for your particular needs. I usually assume that 12" from vertex to vertex is more than adequate for my needs. Further, use common sense and visually verify that the "simplify" command isn't tweaking the data too badly. You can always hit "Undo" and rerun the command with a different setting.

Once this is done, select all the 3d poly's and run the "Create Site Model" command. If you've followed all the steps you should end up with a very life-like model (of course depending on how accurate the survey was in the first place). FWIW, I have accomplished some truly extraordinary things in the real world by these methods. Things I never would have attempted prior to having these tools.

Hope that helps!

Peter

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I posted this in the general discussion area, in a thread that went nowhere, but repost it here in case you didn't see it.

First, as far as I can tell, there is no reason not to just convert the polylines directly to 3D Polys, using the Modify>Convert to 3D Polys. Yeah, you have to set each Z value but I have never seen a topo map yet drawn perfectly from low to high contour.

I was testing things this morning by drawing a 10 acre freehand polyline at 200 scale as a test. On high smoothing it came out to 21 vertices.

At low res conversion, that freehand polyblobs converted to 81 vertices when converted to either a 2 or 3D polygon. (High res was 787 - No need to go there!)

Accepting the VW suggested filtering cut the vertices by about half (to 36), setting it to 2X the recommended filter reduced it to 34, 5X to 26 and 10X right back to my initial 21 vertices.

I agree you need to study each contour to make sure you have the right trade off vertices and accuracy, but in general, I would double the recommended value in the simplify command, at least.

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Peter & Rosford,

I had some success with Peter's method. Copy>Paste in Place in ascending order & using the Survey Input 2D Contours to 3D Polys>Create 3D Loci but this was time consuming as so many of the contours needed to be retraced/connected due to the retaining walls, etc.

What I did instead was Copy>Paste in Place or retrace the major contours (10'-0" interval). Then 2D Contours to 3D Polys>Create 3D Loci>Terrain>Create Site model & set my minor contour interval to 2'-0" the same as the original survey. I have an 80'-0" change in elevation over a 3 acre site.

The result was very near the original survey and certainly adequate for me to cut some major sections through.

If I can get 3D loci to appear in the minor contour interval I can simply drag those Loci to align over the existing survey and have a very good result.

I will experiment with the Convert to 3D Polys method tomorrow and report back.

Thanks,

Jeremy

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Jeremy,

My problem has usually been larger sites and many swales and watersheds make it hard to actually get the contours in any ascending order. 2D to 3D contours is probably better on a simple site, and quicker, but I find myself having to assign the Z value manually many times.

Good luck!

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Peter & Rossford,

I had similar success converting polygons to 3D Polys>setting the Elevation for Each then creating the site model.

Peter, I am curious about the following portion of your original response:

"The next step, before actually creating the Site Model is to run the AEC>Terrain>Simplify 3d Polygons command. "

Under AEC>Terrain I have only (5) options:

1) Create Site Model

2) Filter 3D Polygons

3) Validate 3D Data

4) Site Model Section

5) Send to Surface

There is no "Simplify Polygons" command.

Is this command somewhere else?

Any thoughts on controlling/moving minor contour intervals generated by the program?

Thanks,

Jeremy

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As far as your second question, there is no easy way I know of to move (or reshape) the interpolated contours generated by the software. It has been "wish listed" to be able to export these as 2d polygons so that they could then be re-used to create a new Site Model, but as of yet this is not possible.

So unfortunately, if you need the Site Model to match the original topog data (which by the way is almost always interpolated as well - the surveyor usually walks the site and takes spot/point data at fairly random, yet critical, points, like the bottoms of walls, etc., then plugs those points into his or her own software) you will need to use more of the original topog data.

One suggestion might be to go back to the 3d polygon step (I always save these on an undisturbed layer somewhere just in case I need to re-create the Site Model) and add in a few highly critical contour lines, like the bottoms and tops of walls, etc.

P

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Re: Simplify Polygons - for some reason, they renamed Filter 3d Polys to Simplify 3D Polys in 2010. Same command, though.

The literature claims that 2010 will be a more stable version of the topo modeling package. We shall see!

I have saved groups of proposed site modifiers/3D polys for future use in other files by grouping them and creating a file I call "topo signatures" but of course, I have to relabel all the lines to correct Z or pad value.

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