I am trying to create a complex model by stacking polygons.
I am obliged to do this since concave surfaces are a no no, as we know.
To eliminate gaps I'm moving the vertices of mating faces so that they are perfectly aligned on the one unit grid.
In modeling view all mating faces are perfectly matched, no overhangs or gaps.
However, when I run the map, the mating faces are askew with gaps and overhangs.
Is there a way to do this or am I asking for geometry that the rendered just can't handle?

Thanks in advance
Mammo

Besides aligning vertexes to the grid, make sure that you're not bending faces in a way that their vertices are no longer on one plane. (Try lifting one corner of a piece of paper: you'll notice that it will bend and become concave.)
If the map compiler comes across a face whose vertices are not on a single plane, it will move vertices as necessary to force it into compliance, causing the alignment to be screwed up. To fix this, you'll need to further split blocks so that the individual faces are not bent like this.

Or you may be able to use a displacement surface. (This may or may not be a good solution depending on the shape you're trying to make.)

Gracias!