DTM with 3D polys: defining boundary

[Scupper]

I'm trying to find a reliable way of making DTMs using 3D polygons and I'm finding it's harder than doing it with spot heights/3D loci.

I've extended my 2D polygons beyond the site boundaries and made sure that they connect (see file, red lines) because otherwise VW only seems to recognize one contour at each height.

I make the site model, then Edit Group and make a polygon to define my site boundaries, then come out of the edit and update the model on the OIP. When I choose extruded countours, I always get a flat platform the shape of my boundary polygon, on top of the model (see pic). It doesn't happen with other display styles, but extruded contours is the one I want.

I'd be really happy if someone could let me know how to correct this.

I'm using V2008 SP2 with Windows XP and have 2GB of RAM.

[Benson Shaw]

Might be a bug or might be a problem with your contours or boundary poly.

Is there an inadvertent duplicate of the boundary poly? One creates the hull for your terrain and the other acts as another contour creating that stadium cover over the bowl. Is the boundary poly closed for sure? Is it a polyline instead of the required polygon?

Or you might have some file corruption. Were any of these contours imported from a dxf/dwg file?

This will not take much effort, but might help or tell you something:

Copy the contours into a new, blank drawing file (use the Paste in Place command), create the terrain on a new layer, add the boundary poly and see what happens. If it behaves properly in extruded contour mode, then copy the contours and new DTM, and Paste in Place into your orig drawing (delete the funky terrain and contours).

If same bad behavior, then cut one contour at a time in the new drawing file, update the DTM each time to see if it works. If no change paste it back in with Paste in Place and cut the next one. If there is a bad contour, replace it with a trace.

Oh well, good luck.

-B

[Scupper]

Thanks, Benson, the highest 3D poly was screwing it up, and removing it worked. Very helpful suggestion. That poly was outside my boundary so removing it doesn't compromise the model.

It's almost perfect now, but there's still a bite out of the base where I'd like a straight edge (see file). Any idea how I can fill it in without getting it clipped? I've tried adding 3D polygons off the boundry below it and I've tried putting in a lower minimum elevation in Site Model Settings but neither seems to work.

[Benson Shaw]

The cheater method: Select the site model. Enter group, Copy the hull poly, Exit group, Paste in Place, Convert to 3d Poly or Extrude the poly (z=minor contour hgt?), raise/lower this new 3d object to appropriate z. It's not part of the site model, but with proper color and line attributes, it can act in concert with the site model.

I think the 3d Extrude cannot make an extrude from the lowest contour. But perhaps others will show a way.

-B

[Scupper]

That'll work, - should have thought of it myself. I just thought maybe I was doing something wrong that could be fixed so the cutout wouldn't happen.

Many thanks again.

[islandmon]

The cheater method: Select the site model. Enter group, Copy the hull poly, Exit group, Paste in Place,

Beware ... there was a symbol XY offset bug in early versions of the DTM. Check the alignments after pasting.

[Benson Shaw]

Islandmon - Actually, I just observed that with one of my test polys for this DTM question, but thought it was a temp error in my system. If I raise or lower a 3d poly with the OIP, sometimes it offsets xy, dramatically. I have not logged whether this happens only when working with DTM related polys or all situations. Anyway, if I switch to a side view and use the move command, there is no apparent offset.

Is this the same bug? My VW 12.5.3 and OS10.4.11 have all the updates.

-B

[Scupper]

Here's the VW file, which I should have posted initially instead of JPEGs. It would still be good to know how to avoid the cutout at the bottom of the model.

The copy and paste 'cheat' worked fine for me and I didn't get any offset error either using the move tool. I guess adding that pasted poly would only be a problem if there were site modifiers affecting that level.

Thanks again.