Normal Tags

Helper

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On 23/11/2005 at 06:42, xxxxxxxx wrote:

User Information:
Cinema 4D Version:   9.1+
Platform:      Mac OSX ;
Language(s) :     C++ ;

---------
Hello,
I am trying to read and write Normal Tag data without success yet.
I understand that the data is stored as a Real value within the WORD values ax...dz, but how do I access these values?
Any ideas?

Helper

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On 23/11/2005 at 21:22, xxxxxxxx wrote:

What do you mean by 'Normal Tags' -- Just a tag that you put on objects in c4d? Sorry for my lack of understanding. I'll try to help if I can. And what are the "WORD" values? Are you by chance thinking of tag containers, or am I completely missunderstanding?

Aaron M.

Helper

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On 24/11/2005 at 00:13, xxxxxxxx wrote:

Hi Aaron,
I am talking about that kind of tags that is generated by Rhino or other NURBS or CAD modellers to store the surface normals in.
Within the SDK this type of tag is labled with Tnormal and the original description there is:

Normals tag. (Contains 12 WORDs per polygon, enumerated like the following: ax,ay,az,bx,by,bz,cx,cy,cz,dx,dy,dz. The value is the Real value of the normal vector component multiplied by 32000.0.)

Finding and reading out the tag data is no problem. I just have no idea how to read and write the ax, ay ... etc components.

Helper

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On 24/11/2005 at 00:25, xxxxxxxx wrote:

Arndt, Tnormal is derived from VariableTag (see docs). That might get you started on finding those values!

Helper

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On 24/11/2005 at 01:09, xxxxxxxx wrote:

Hi Robert,
yes, thank you, I already know that (see copied Tnormal description in my last posting).
It's just that I have no idea how to access those Real elements.

Right now I am using:

VariableTag *tag=NULL;
Real *Normale=NULL;
LONG Elements;

tag=(VariableTag* )object->GetFirstTag();
while (tag)
    {
    if (tag->IsInstanceOf(Tnormal))
         {
         Normale=static_cast<Real*>(tag->GetDataAddress());
         Elements=tag->GetDataCount(); // Polygone

for (i=0; i<Elements; i++)
              {
               // Is Real the right type for the tag data array?
               // How do I get ax, ay, az etc. here?
               }
          }
      tag=(VariableTag* )tag->GetNext();
     }

Helper

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On 24/11/2005 at 02:46, xxxxxxxx wrote:

I think their clue is that the data contains an array of '12-WORD' values, the array being 12 WORDs * polygon count. As to the procedure for extracting the data, I have no idea. It seems that the WORDs are pseudo-integers which need to be divided by 32000.0 to get the REAL value back out:

WORD* Normale = NULL;
...
ax = (Real)Normale[n] / 32000.0; (or more efficiently multiplied by 1/32000.0 = 0.00003125)
(etc.)

Your best bet to determine whether one element of the array is 12-WORDs or 1-WORD is to use GetDataSize() and see what it returns. But, I donot think that the data is parsed out in either polygons or Real values, but in WORDs which need interpretation.

Helper

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On 24/11/2005 at 09:24, xxxxxxxx wrote:

Hi Robert,
the problem is that looking at the data count with tag->GetDataCount() gives the number of polygons of that object.
So the array has only as many elements as there are polygons, but as there are 12 numbers stored for each polygon within that array, I have no idea how the read them out.
I already tried to add .ax, .ay etc to the read out value. Doesn't seem to work that way:
Real value=Normale _.ax

Helper

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On 24/11/2005 at 11:24, xxxxxxxx wrote:

Hello Arndt,

My thinking is that there is no single 'element'. You'll need to extract 12 WORDs at a time, into a temporary buffer perhaps:

  
VariableTag* tag=NULL;  
WORD* Normale=NULL;  
LONG Elements;  
WORD wNormal[12];  
LONG j;  
  
tag=(VariableTag* )object->GetFirstTag();  
while (tag)  
{  
     if (tag->IsInstanceOf(Tnormal))  
     {  
          Normale=static_cast<WORD*>(tag->GetDataAddress());  
          Elements=tag->GetDataCount(); // Polygone  
            
          for (j=0; j<Elements; j++)  
          {  
               CopyMem(Normale[j],&wNormal;[0],12*sizeof(WORD));  
               // Each component is then an index into wNormal  
               // i.e.: ax = wNormal[0], dz = wNormal[11]  
          }  
     }  
     tag=(VariableTag* )tag->GetNext();  
}

Note that you still need to do the conversion (Real = WORD / 32000.0) and the referencing of Normale might need to be &Normale;[j][0] or you may need to increment Normale by 12 WORDs each time (Normale += 12 for each j loop). Not certain.

Helper

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On 25/11/2005 at 02:31, xxxxxxxx wrote:

Thank you very much Robert, but this doesn't work either.
In the meantime I got a hot tip from MAXON about this. Here is the solution:

struct NormalStruct
{
Vector a,b,c,d;
};

NormalStruct NormalTag::GetNormals(LONG i)
{
     NormalStruct ns;
     i*=12;
     WORD *ndata=(WORD* )t_data;

ns.a=Vector(ndata[i+0],ndata[i+1],ndata[i+2])/32000.0;
     ns.b=Vector(ndata[i+3],ndata[i+4],ndata[i+5])/32000.0;
     ns.c=Vector(ndata[i+6],ndata[i+7],ndata[i+8])/32000.0;
     ns.d=Vector(ndata[i+9],ndata[i+10],ndata[i+11])/32000.0;

return ns;
}

Helper

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On 25/11/2005 at 11:33, xxxxxxxx wrote:

Well, I'm so glad that they passed this information along in the SDK documentation!

Helper

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On 26/11/2005 at 03:32, xxxxxxxx wrote:

Well the SDK docs say:
"Normals tag. (Contains 12 WORDs per polygon, enumerated like the following: ax,ay,az,bx,by,bz,cx,cy,cz,dx,dy,dz. The value is the Real value of the normal vector component multiplied by 32000.0.)"
Thats pretty clear. It tells you there are 12 WORDs per polygon, and what those 12 WORDS are (x,y,z) for the a,b,c,d of each polygon, plus how to get from the WORD value to the real ones.

Helper

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On 26/11/2005 at 11:40, xxxxxxxx wrote:

If 'twere so clear, why does this thread exist? ;0)

I had a general idea about how it might work only from working with other VariableTags. But I didn't have time to do the actual testing (just a tad busy updating and fixing one of my plugins) and hadn't the need to deal with them previously.

Clarity is contextual.