OK, so what am talking about?  First, lets define a few things.  Map 3D can build a topology; which is a generic GIS term for polygon shapes. These shapes can contain curves.  You ask yourself – But you said they’re not really curves? I know. I know.  Read on for the details….

 

When you create a topology from lines, arcs, polylines with curves, everything gets created as intended.  No tessellation worries yet.

 

However, once you need to overlay 2 topologies (let’s say a soils layer with a mapbook grid), all  curves get tessellated, no apparent rhyme or reason. In the sample below, you see a curbed island layer with curves and the resulting overlay with another layer.  The result is the grips shown.  You can see the amount of tessellation per curve does seem to be random.

If those original curves cross the bounding topology the tessellation will still occur, but now the curve defining your desired area has been moved.

For small curves, this seems to be within a general tolerance for hydrology, but what if you couldn’t accept any tolerance errors?  I am in touch with the Desk to see what our options are.  Stay tuned….