Patchy Polygon

03-21-2013 07:30 AM
New Contributor

I'm having trouble with polygon fill appearing patchy when rendered either with a color or image and aligned (align shape to terrain) to a terrain that has an image draped on it.  It appears as though part of the image is falling under the surface .  (see attached)  I tried aligning the terrain to shape with only a slight improvement. 

Items of note:
1. the terrain and the image are the same extent.
2. portions of the outside boundary of the terrain are 0 value.  it was derived from contours that were clipped.  The range of the height values is from 0 to 679 with all the non-zero values falling between 579 and 679. 
3. none of the features on this polygon layer fall outside of the area of non-zero value terrain

Has anyone had similar issues?  I'm actually looking to bring in many more polygon layers to cover a good portion of the terrain.

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4 Replies
New Contributor III

The reason why the polygon looks "patchy" when you drape it onto the terrain is that when you align shape to the terrain, CE only tries to align the edges of the polygon. The poly is a solid shape (a plane) so it can't wrap itself to drape over the terrain. You would have to break it up into triangles (tin) in order to conform to terrain. I had a similar result when I tried to import parcel shapes on top of my terrain.

Hope this helps.

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Frequent Contributor
You can of course also align the terrain to shapes.

So you have both options :
- align shapes to terrain
- aligning terrain to shapes

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New Contributor
Thanks for the reply Scott.  The rendering capabilities of CityEngine is one of the things I had looked forward to using on not only the 3D faces but also 2D vector data. Of course I do realize that the main purpose of CE is rendering 3D objects so I will probably look at some other options.

Matt, I think I'm grasping at straws but I wanted to check to see if it is your expectation that the issue would be solved by aligning the terrain to the shapes.  I ask because I did try this after aligning the aligning the shapes to terrain but only had a slight improvement.  I have to align the shapes first because the shapes are at Z=0.  Is there another workflow that you see working?

Thanks again to you both!
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Frequent Contributor
Hi Jim,

The main taks when working with CityEngine is to produce 3d Models procedurally. CE ist a 'procedural modeling application'.

CityEngine is NOT a visualization tool.

The terrain modeling features are still limited in CityEngine, we know. Currently, the way described is the best workflow.

-> Align Shapes to Terrain
-> Align Terrain to Shapes

Maybe try to increase the U and V subdivisions of the terrain. For this, select the terrain layer and check the Inspector.

Ok ?
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