What is the best manner to reduce the number of polygons of a model with 2 millions of faces to 50 000 faces?

Polyreduce SOP or “greduce” standalone…

When I reduce the model I get a triangulated model (something similar to the left sphere). Is it possible to get a reduced polygonal model with a nice layout of polygons in rows and columns like the sphere of the right?

The PolyReduce SOP “requires (and outputs) a triangular mesh”. In other words you are limited to getting triangles.

Remember if you are doing heavy poly reduction you might need to turn up the Equalize edges option way beyond 1 - the natural limit of the parameter slider - try 10 or even 100.
If you don't you might not even get nicely distributed triangles.

I added this as a user note to the help but it seems to have now been removed, or gone missing….

fruela
When I reduce the model I get a triangulated model (something similar to the left sphere). Is it possible to get a reduced polygonal model with a nice layout of polygons in rows and columns like the sphere of the right?

I don't think there is a software in the world that will do that. At least not with many more steps and manual work involved.

I don't think there is a software in the world that will do that.

Well, it's probably true, but Polygon Reduction operator in XSI is perhaps the closest thing to that.
At least it has this nice Quad Preservation feature.

fruela
When I reduce the model I get a triangulated model (something similar to the left sphere). Is it possible to get a reduced polygonal model with a nice layout of polygons in rows and columns like the sphere of the right?

Gruezi - If you have a grid of polys to begin with, you could try converting the polys to a mesh primitive, then use the unrefine SOP to thin it out, and if need be, convert back to polys at the end.

– Antoine

Using xsi is a dream when it comes to poly's