meshes from Rhino

 From:  Michael Gibson
2669.4 In reply to 2669.3 
Hi andras,

> Sorry, I dont understand what is the distinction between
> IGES and OBJ "flat surface" ...

IGES contains NURBS surfaces, which are the kind of data that MoI works with - where surfaces are not just made up of triangles, they are a kind of "spline", meaning a mathematically smooth object that is made up of control points.

OBJ data is much different - it stores data made up of a whole lot of little flat facets (polygons).

It is possible to transfer a "sub-d" cage of facets between sub-d modelers with OBJ format, that basically interprets the polygon data as a similar kind of control cage as a spline. But MoI does not work on that kind of sub-d data, MoI works on NURBS data.

So that's the main difference - IGES stores NURBS surfaces and OBJ stores polygon data.

MoI can produce polygons from NURBS surfaces, which is what happens if you save from MoI to OBJ format. But it is not easy to go the other direction and try and re-make larger smooth NURBS surfaces from a set of diced up flat polygons. That's why MoI does not currently open OBJ files directly, because that is not the kind of data that MoI is set up to work on.

Let me know if this still doesn't make sense and I will see if I can explain it in a different way.

But basically there is not just one single method that 3D objects are stored in, there are several different methods for how 3D objects can be structured. OBJ contains one method (polygons) and IGES contains a much different method (trimmed NURBS surfaces).

- Michael