Working in Blender (2.49b), I have grouped an object to vertex groups.  All is well.

I then export as Wavefront OBJ (always sure to have polygroups and vertex order set), and all seems well.  But I found that I ran into a number of vertices error in Poser trying to load a morph target.

What I found was that the export changed my grouping.  Enough to screw up the counts in each group!?

This is a picture of the original OBJ after I grouped it with the "hip" group selected on the left.  It was then exported.  On the right, is the re-imported object.  As you can see, "hip" selected...it changed a row from "abdomen" to "hip".  In this case the "hip" originally had 909 vertices, after export it had 973...ugh.

[PICTURE LINK]

If I then Export/Import again, no changes.  So it must be something I am doing, or fail to do before/during export?  Any thoughts?

When grouping I am using Vertex Select Mode, and basically work up the object.  So I group the "hip" first in this case.  Then I select basically most of the "hip" and work up the abdomen...then "Desel." the hip before assigning to the abdomen.

Are you using the Polygroups option in the export dialog box? It's deselected by default but it needs to be used to preserve the order of the groups.

Yes, I am, both on export and re-import....and thanks for getting that added to blender!  I also make sure Vertex Order is also selected.

I'd be happy to send you a .blend file if you want to test an export of it.  It seems to be very repeatable.  I am just using a derivative of the free Omnisuit OBJ that @corinthianscori made and is on ShareCG for learning, so I would not be losing anything ;-)

OK, I think I figured it out.  Its in the grouping process I was using.  Best to explain with an example:

Lets say there are 9 vertices (which make 4 faces), and I wanted Group1 to be assigned the lower 2 faces, and Group2 to own the upper 2 faces:

1-2-3
4-5-6
7-8-9

and I assigned 4,5,6,7,8 and 9 to Group1

The I selected all, and deselected vertices from Group1 and assigned the remaining to Group2, which would leave only 123 assigned to Group2

If you are going by "faces" it leaves the bottom faces belonging to Group1 (good!), but the upper faces bound by 1/2/4/5, and 2/3/5/6 not really part of either group.

To do this, vertices 4, 5 and 6 must belongs to both Vertex groups.

Looks like you can't use the deselect from the other group, unless you plan to go back and add some back.  The polygroup export just made a decision on this and made some assignments.

I am curious what other process anyone uses for grouping in Blender?

Going by your explanation of how vertex groups are implemented by Blender, you will have to split the mesh at group boundaries (so that there are duplicates of all vertices that form the group boundaries).

For making morph targets for Poser figures I prefer to run them through Composer first.  This utility create new mesh with no groups and welded seams.  The problem is I can't find a link for it, so it may not be available anymore

EDIT

I did find a tutorial download for using Composer.

http://www.4shared.com/get/34675269/549fa5f6/Using_Compose_and_Blender_to_m.html;jsessionid=9B85052EF17FEA8365AE3B01A0FAB8AC.dc210

I found it on Morphography

I cant remove the groups though, since Poser 7 seems to require the morph targets be loaded by Group?

Attached Link: http://poserpros.daz3d.com/forums/viewtopic.php?p=370035#370035

Actually removing the groups (and so working on a single welded mesh) is the best way, but you need to use something like UVMapper to save the group information so that it can be added back to the morphed mesh (see attached link).
Where possible/practical always work from the original OBJ not an export.

I've found that I'm best setting my groups in Blender in face mode and not in vert or edge mode. That way nothing gets left out. Just a thought.

 Just to make it clear. OBJ groups are actually groups of FACES. In other words, the OBJ format doesn't group vertices but polygons.
When I added support for groups in Blender I used the vertex groups because that's what was available. Blender vertex groups were not exactly meant for that but it was the best thing available. So, yes, keep in mind that when you select/deselect parts of the model you should strictly operate in face selection mode.

Hope this helps.

True, but you have to be careful though, even in face selection, if you use "deselect" (even in face mode) you will still deselect the vertices.  I saw this problem when using face selection, so switched to vertice selection.  It was not obvious, but I was getting the same result.

So in the sample above, if I selected the bottom 2 faces, it is equivalent to the example.  And when I deselect it does the same.

I always deselect by using the A key, that way I know that I'm deselecting everything

Composer puts the groups back into the morphed mesh when you are done.  It create a special map file that saves the grouping.

Quote -
Looks like you can't use the deselect from the other group, unless you plan to go back and add some back.  The polygroup export just made a decision on this and made some assignments.

I am curious what other process anyone uses for grouping in Blender?

In case anyone later reads this, I found a solution. 

If you are working in Face Select Mode in Blender, instead of using "Deselect", you can "Select", and then use HKEY (or Mesh->Show/Hide Vertices->Hide Selected).  Though it is a Hide vertices command, if you are in Face mode, it will actually hide only the vertices that complete a face. 

For example, group the lShin, and then Select/Hide the group before grouping the lThigh

Woohoo!

(its probably what @RobynsVeil was talking about, but took me this long to get it ;-)

Quote - > Quote -

Looks like you can't use the deselect from the other group, unless you plan to go back and add some back.  The polygroup export just made a decision on this and made some assignments.

I am curious what other process anyone uses for grouping in Blender?

In case anyone later reads this, I found a solution. 

If you are working in Face Select Mode in Blender, instead of using "Deselect", you can "Select", and then use HKEY (or Mesh->Show/Hide Vertices->Hide Selected).  Though it is a Hide vertices command, if you are in Face mode, it will actually hide only the vertices that complete a face. 

For example, group the lShin, and then Select/Hide the group before grouping the lThigh

Woohoo!

(its probably what @RobynsVeil was talking about, but took me this long to get it ;-)

Kind-of, but your solution is quite elegant. Thank you for sharing it with us!

By the way, are you using the Polygroups option in the export dialog box?

Yes I am!