[osg-users] Textured ply file is black when loaded.

'Tom Pollok' via OpenSceneGraph Users osg-users at googlegroups.com
Tue Jan 21 06:23:48 PST 2020

Also it seems that its not the method

void VertexData::readVertices( PlyFile* file, const int nVertices, const int 
fields )

that needs to be adapted, but 

void VertexData::readTriangles( PlyFile* file, const int nFaces )

which actually parses the faces.

Am Dienstag, 21. Januar 2020 15:07:35 UTC+1 schrieb Tom Pollok:
> Hi Robert,
> oh i didnt mean you to do a deep investigation, i just thought it was a 
> bug or at least you might know if im doing sth wrong.
> I investigated a little.
> So it seems that the comment for texture files is actively used:
> comment TextureFile YourTexture_material_0_map_Kd.jpg
> So that needs to be parsed, and not ignored as just being a comment.
> The tools i used (MeshLAB and CloudCompare) are widely used in the 
> research community or industry. I guess there is no perfect documentation 
> that keeps track of every "hack", in case that is it is one.
> Regarding the header, ill add comments from what i understood 
> ply
> format ascii 1.0
> comment VCGLIB generated
> comment TextureFile Wareneingang_material_0_map_Kd.jpg
> element vertex 99428 //number of vertices
> property float x  //vertex X coordinate
> property float y  //vertex Y coordinate
> property float z //vertex Z coordinate
> element face 186642 //number of faces
> property list uchar int vertex_indices    //means that a face consists of 
> a number of vertices, the first uchar states that there is a n uchar at the 
> beginning that states the number of vertices that make a face. Typically 
> that is 3, but thats then in the ascii or binary dump. So assuming there 
> are 3 vertices, then 3 ints (vertex indices) have to be parsed.
> property list uchar float texcoord //after the vertex indices there is a 
> list of float texture coordiantes. The uchar states the number of values. 
> So this has to be interpreted as uv coordinates like (U0, V0, U1 V1, ..., 
> Un Vn), as there are 3 vertices, there will be three times two (u+v) == six 
> floats. The U V coordinates are typically in a rage between 0/0 to 1/1, but 
> i read somewhere that they could be larger which could mean a mirroring or 
> some sort of repetition. But lets assume they are always in the range of 
> 0/0 to 1/1. 
> property uchar red  //not sure, probably a default color if the number of 
> uv coordiantes was zero because there is no texture file?
> property uchar green //not sure, probably a default color if the number 
> of uv coordiantes was zero because there is no texture file?
> property uchar blue //not sure, probably a default color if the number of 
> uv coordiantes was zero because there is no texture file?
> property uchar alpha //not sure, probably a default color if the number 
> of uv coordiantes was zero because there is no texture file?
> end_header
> I converted the binary ply to ascii ply and there is one line of a vertex:
> -7.326906 -0.92065 -15.26979 
> So x y z totally makes sense.
> Here is the line of a face:
> *3* 74350 89839 97021 *6* 0.670419 0.990827 0.669870 0.993111 0.668217 
> 0.991639 255 255 255 255
> So the explanation in the header makes sense.
> It seems like this shouldnt be to difficult to implement. But i can't 
> promise that I'll find the time to make a PR that fixes that issue. 
> But at least wanted to have this documented in case somebody else is 
> running into that issue.
> Am Dienstag, 21. Januar 2020 12:47:08 UTC+1 schrieb Robert Osfield:
>> Hi Tom,
>> FYI, it's was a community submission back in 2009, I don't personally 
>> know the ply format or have done anything more than cosmetic work on this 
>> plugin.  I basically in the same boat as yourself in terms of ability to 
>> debug the format, I just have to look at the code and see what it's doing 
>> with your file.  It could be a buggy file, or a buggy plugin, or perhaps a 
>> revision to the ply specs since the OSG plugin was written.  The 
>> investigation might determine which.
>> I have begun looking into the issue with reading your ply file, I just 
>> get a grey model right now.  Converting to .osgt using:
>>    osgconv Wareneingang2.ply test.osgt
>> And then looking the test.osgt in an editor reveals that the model has no 
>> texture coordinats.
>> The next step was to add some debugging to the ply plugin to see what was 
>> happening in texture coordinates code:
>> diff --git a/src/osgPlugins/ply/vertexData.cpp 
>> b/src/osgPlugins/ply/vertexData.cpp
>> index f2db29e00..58293f8dd 100644
>> --- a/src/osgPlugins/ply/vertexData.cpp
>> +++ b/src/osgPlugins/ply/vertexData.cpp
>> @@ -174,6 +174,9 @@ void VertexData::readVertices( PlyFile* file, const 
>> int nVertices,
>>              _texcoord = new osg::Vec2Array;
>>      }
>> +    std::cout<<"fields = "<<(fields)<<std::endl;
>> +    std::cout<<"fields & TEXCOORD = "<<(fields & TEXCOORD)<<std::endl;
>> +
>>      // read in the vertices
>>      for( int i = 0; i < nVertices; ++i )
>>      {
>> The result was that the plugin wasn't detected any valid texture 
>> coordinates as the field mask didn't enable TEXCOORD , so then I looked 
>> header parsing code and it looks like:
>>            // determine if the file stores vertex colors
>>             for( int j = 0; j < nProps; ++j )
>>             {
>>                 // if the string have the red means color info is there
>>                 if( equal_strings( props[j]->name, "x" ) )
>>                     fields |= XYZ;
>>                 if( equal_strings( props[j]->name, "nx" ) )
>>                     fields |= NORMALS;
>>                 if( equal_strings( props[j]->name, "alpha" ) )
>>                     fields |= RGBA;
>>                 if ( equal_strings( props[j]->name, "red" ) )
>>                     fields |= RGB;
>>                 if( equal_strings( props[j]->name, "ambient" ) )
>>                     fields |= AMBIENT;
>>                 if( equal_strings( props[j]->name, "diffuse_red" ) )
>>                     fields |= DIFFUSE;
>>                 if (equal_strings(props[j]->name, "specular_red"))
>>                     fields |= SPECULAR;
>>                 if (equal_strings(props[j]->name, "texture_u"))
>>                     fields |= TEXCOORD;
>>                 if (equal_strings(props[j]->name, "texture_v"))
>>                     fields |= TEXCOORD;
>>             }
>> So... the plugin is only checking for texture_u and texture_v, but if we 
>> look at your .ply file the header has: 
>> ly
>> format binary_little_endian 1.0
>> comment VCGLIB generated
>> comment TextureFile Wareneingang_material_0_map_Kd.jpg
>> element vertex 99428
>> property float x
>> property float y
>> property float z
>> element face 186642
>> property list uchar int vertex_indices
>> property list uchar float texcoord
>> property uchar red
>> property uchar green
>> property uchar blue
>> property uchar alpha
>> end_header
>> Which suggests it only has a single texcoord, no texcoord_u or texcoord_v 
>> field that the OSG is assuming is required for textured ply files.  For a 
>> 2D textured file I would expect two fields, like the head explicitly has to 
>> the x, y, z and red, green, blue, alpha values.
>> Does texcoord now implictly mean a x,y value?  Is there some other 
>> encoding?
>> A quick search online for the spec takes me to:
>>    http://paulbourke.net/dataformats/ply/
>> Which doesn't say anything explicit about texcoords so it looks like this 
>> is user definable in which case how to interpret things could be really 
>> open ended.
>> I haven't yet found any explanation online about what is expected in this 
>> case.  I know nothing about the tools you've used to create the file.  This 
>> my first experience with looking into the PLY spec and the actual file 
>> format and haven't away knowing is there is any official guide to what 
>> should be doing with files which using the texcoords field.  To me it looks 
>> like some tools have decided on their own convention and some other tools 
>> honour this, but without know exactly what it is I don't have anything to 
>> go on to make modifications to the OSG's ply plugin.
>> I have to defer further work on this to members of the community that 
>> actually use PLY files in their applications, you will have more knowledge 
>> than myself and what might be meant.

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