[osg-users] Wrong vertex count when loading OBJ files.

[Morné Pistorius]

Hi guys,
I see a strange problem when I load OBJ files.  I use osg::readfilenode() to
load an .obj with a known number of vertices, and then inspect the resulting
node to see how many vertices was loaded, like so:

//debug
osg::Node* node = osgDB::readNodeFile(
C:/Data/Meshes/Hand3DIS/Hand3.obj );
osg::Geode* g = dynamic_cast osg::Geode* (
node-asGroup()-getChild(0) );
osg::Geometry * gm = g-getDrawable(0)-asGeometry();
osg::Vec3Array * v = (osg::Vec3Array*) gm-getVertexArray();
std::cout  verts:   v-size()  std::endl;

I know my model has 7570 vertices (I inspected the contents of the file, and
this is also reported by other obj loaders I tried).  but when osg loads
this file, it reports 'verts: 8369' in the code above.  I need a one to one
mapping between osg's vertices and the ones specified in the obj file.  Does
osg somehow try to automatically optimise the geometry when it is loaded,
i.e create triangle strips, etc.

Funny thing though, when I subsequently save the node to .obj using osg, it
saves it with the correct no of vertices.

Any ideas?

Thanks,
Morne
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Re: [osg-users] Wrong vertex count when loading OBJ files.

[Rosario Leonardi]

At rendering time every polygon attribute must correspond to the 
polygon, so (I guess that) if a vertex of your mesh have two normal (or 
two color) the loader have to split in the vertexes in two.
Try to load a mesh with only smooth edges and the vertexes count should 
be correct, than try to load a Cube, and if I'm right it should have 24 
vertexes.


At save time the vertexes can be grouped again.

Morné Pistorius ha scritto:

Hi guys,

I see a strange problem when I load OBJ files.  I use 
osg::readfilenode() to load an .obj with a known number of vertices, 
and then inspect the resulting node to see how many vertices was 
loaded, like so:


//debug
osg::Node* node = osgDB::readNodeFile( 
C:/Data/Meshes/Hand3DIS/Hand3.obj );
osg::Geode* g = dynamic_cast osg::Geode* ( 
node-asGroup()-getChild(0) );

osg::Geometry * gm = g-getDrawable(0)-asGeometry();
osg::Vec3Array * v = (osg::Vec3Array*) gm-getVertexArray();
std::cout  verts:   v-size()  std::endl;

I know my model has 7570 vertices (I inspected the contents of the 
file, and this is also reported by other obj loaders I tried).  but 
when osg loads this file, it reports 'verts: 8369' in the code above. 
 I need a one to one mapping between osg's vertices and the ones 
specified in the obj file.  Does osg somehow try to automatically 
optimise the geometry when it is loaded, i.e create triangle strips, etc.


Funny thing though, when I subsequently save the node to .obj using 
osg, it saves it with the correct no of vertices.


Any ideas?

Thanks, 
Morne









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