get position of ofxAssimpModelLoader mesh

[minusplusminus]

Hi,

I'm trying to get a position of a mesh from Assimp. But I could not figure out how. Is there a simple solution for this? This could be a handy feature.

[wasawi]

+1

[minusplusminus]

I've allready made some code for getting the verticles. I still can't figure out how to get the position of the mesh:

      vector<ofPoint> ofxAssimpModelLoader::getMeshVerticles(int meshIndex)
 {
     aiMesh * mesh = getMeshHelper(meshIndex).mesh;
     aiVector3D* aiPts = mesh->mVertices;

     for(int x=0; x<mesh->mNumVertices; x++ )
     {

         Pts[x] = ofPoint(aiPts[x].x,aiPts[x].y,aiPts[x].z) * normalizedScale;

     }
     return Pts;
 }

[bilderbuchi]

This feels like it would be more appropriate in the forum, but in any case, @openframeworks/2d-3d, can you help?

[elliotwoods]

I presume that using the mean of the vertices isn't a solution

I'm not familiar with Assimp, but if it's like ofMesh, then the mesh itself doesn't have a position, but the individual vertices do. Which means that your question can usually mean either:
A) what's the mid point of the bounding box
B) what's the mean vertex position

[danzeeeman]

you need to get the matrix of the individual mesh from ofxAssimpModelLoader

I exposed it in a branch here https://github.com/danthemellowman/openFrameworks/blob/ofxassimp-update-access-mesh-matrix/addons/ofxAssimpModelLoader/src/ofxAssimpModelLoader.cpp#L827

but you can also just get the MeshHelper for a given mesh and get the matrix from that.

https://github.com/openFrameworks/openFrameworks/blob/master/addons/ofxAssimpModelLoader/src/ofxAssimpModelLoader.cpp#L580

[danzeeeman]

You can also do something like this and get the bounding box of the mesh and then find the center point.

https://github.com/YCAMInterlab/mapamok/blob/master/SharedCode/MeshUtils.h#L305

[julapy]

here is how ive been creating a duplicate mesh from a model and transforming it back into world space. you need to create a ofMatrix4x4 which is combination of the model matrix and the mesh matrix, once you have this, you can re-calculate your mesh back into world space like below. using this approach, you can also re-calculate the mesh position back into world space.

i do this quite a bit when working with ofxAssimpModelLoader and looks like others do too.
perhaps this should be a feature in ofxAssimpModelLoader?

    int meshIndex = 0;
    ofMatrix4x4 modelMatrix = model.getModelMatrix();
    ofMatrix4x4 meshMatrix = model.getMeshHelper(meshIndex).matrix;
    ofMatrix4x4 concatMatrix;
    concatMatrix.preMult(modelMatrix);
    concatMatrix.preMult(meshMatrix);

    ofMesh mesh = model.getMesh(meshIndex);

    for(int i=0; i<mesh.getNumVertices(); i++) {
        ofVec3f & vert = mesh.getVertices()[i];
        vert.set(concatMatrix.preMult(vert));
    }

cc @ikillbombs @wasawi

[edap]

What if, ofxAssimpModelLoader, when importing the meshes, convert them to of3dPrimitive?
of3dPrimitive has ofNode, and all the meshes belonging to the same model could have as parent an ofNode that defines the position of the model.
In this way it is also easier move the model around and getting the position.

[NickHardeman]

Each node in ofxAssimp extends ofNode, ie meshes and bones. Meshes have both local and global bounding boxes and a center location. Functions have been added to get the transformed vertices as ofMeshes.

openFrameworks/addons/ofxAssimp/src/ofxAssimpModel.h

Lines 175 to 182 in 5b651b9

	/// \brief Get a transformed OF mesh based on name of assimp mesh.
	/// \param aname name of the desired assimp mesh.
	/// \return Transformed ofMesh.
	ofMesh getTransformedOFMeshForMesh(const std::string& aname);
	/// \brief Get a transformed OF mesh based on the vector index of the assimp mesh.
	/// \param ameshIndex vector index of the assimp mesh.
	/// \return Transformed ofMesh.
	ofMesh getTransformedOFMeshForMesh(unsigned int ameshIndex);

closed by #7776