Join surfaces & orientation

Here is a polysurface viewed in backface mode.

Faces don’t get a coherent orientation when joined. There must be something wrong with this polysurface, but how to find what’s wrong ?
2014-07-12 join & faces (1.0 MB)

Have you tried to see if there are naked edges using the ShowEdges command? I have had similar experiences in the past and usually the boundary between ‘up’ and ‘down’ surfaces is a naked edge.

At the boundaries and where the surfaces change orientation, you have naked edge, even if it is all one polysurface. But if you explode and join manually (joining one surface at time), you can join well surfaces that are up and down when joining all at once.
There is no bad object.

All surfaces joined at once:

Polysurface exploded and then joined manually

It seems the Join command has trouble with these large sets of surfaces being joined. I have encountered this when joining many surfaces of ship hulls coming from NAPA design software.

For example this

I find that this is usually caused by edges not overlapping within tolerance. The picture above, for example, was made for a model that had a tolerance of 1 micrometer on a ship length of approx 200m. When reducing the tolerance to 1 millimiter, the join proceeds without this orientation problem.

Hi Alan - Thanks, I’ll take a look.

Your object is very very large, and the file has no units… what is the origin of this file?


Hi Pascal,

The relief was first produced in Lands Design with Google Earth import,
then worked in a Rhino file with mm model unit
and finally one polysurface was exported to the current file.