Problem joining polygons with Z values

[José Luis Esteban]

Hi!

I'm using Clipper version 6.1.5 of 28 March 2014 in c++.
Trying to join polygons using Z values I found the following:

/*
                +----------+                         +----------+
                |          |                         |          |
                |      b   |                         |          |
    +-----------+---+      |             +-----------+          |
    |           |   |      |    Union    |                      |
    |           +---+------+   ------>   |               +------+
    |               |                    |               |       
    |      a        |                    |   expected    |       
    |               |                    |               |       
    |               |                    |               |       
    +---------------+                    +---------------+       
*/
Path a, b;
a << IntPoint(0,0,0) << IntPoint(10,0,0) << IntPoint(10,10,0) << IntPoint(0,10,0);            
b << IntPoint(8,8,0) << IntPoint(14,8,0) << IntPoint(14,14,0) << IntPoint(8,14,0);

Clipper c;
c.AddPath(a, ptSubject, true);
c.AddPath(b, ptClip, true);
Paths solution;
c.Execute(ctUnion, solution, pftNonZero, pftNonZero);
cout << endl;
for (IntPoint ip : solution[0]) cout << ip.X << ", " << ip.Y << ", " << ip.Z << endl;

The above code produces a correct result:

10, 8, 0
14, 8, 0
14, 14, 0
8, 14, 0
8, 10, 0
0, 10, 0
0, 0, 0
10, 0, 0

But then I try to do the same using 10 for all Z values:

Path a10, b10;
a10 << IntPoint(0,0,10) << IntPoint(10,0,10) << IntPoint(10,10,10) << IntPoint(0,10,10);
b10 << IntPoint(8,8,10) << IntPoint(14,8,10) << IntPoint(14,14,10) << IntPoint(8,14,10);

Clipper c10;
c10.AddPath(a10, ptSubject, true);
c10.AddPath(b10, ptClip, true);
Paths solution10;
c10.Execute(ctUnion, solution10, pftNonZero, pftNonZero);
cout << endl;
for (IntPoint ip : solution10[0]) cout << ip.X << ", " << ip.Y << ", " << ip.Z << endl;

And the result is:

10, 8, 0
14, 8, 10
14, 14, 10
8, 14, 10
8, 10, 0
0, 10, 10
0, 0, 10
10, 0, 10

Where the first and fifth Z values should be 10.

Is there anything I'm doing wrong?
JL

[José Luis Esteban]

Some additional information:

The union of two adjacent rectangles works when Z values are 0:

Path a1, b1;
a1 << IntPoint( 0,0,0) << IntPoint(10,0,0) << IntPoint(10,10,0) << IntPoint( 0,10,0);
b1 << IntPoint(10,0,0) << IntPoint(15,0,0) << IntPoint(15,10,0) << IntPoint(10,10,0);
Clipper c1;
c1.AddPath(a1, ptSubject, true);
c1.AddPath(b1, ptClip, true);
Paths solution1;
c1.Execute(ctUnion, solution1, pftNonZero, pftNonZero);
cout << endl;
for (IntPoint ip : solution1[0]) cout << ip.X << ", " << ip.Y << ", " << ip.Z << endl;

Produces a correct result:

0, 0, 0
15, 0, 0
15, 10, 0
0, 10, 0

But when the Y dimension is interchanged with the Z dimension:

Path a2, b2, e2;
a2 << IntPoint( 0,0,0) << IntPoint(10,0,0) << IntPoint(10,0,10) << IntPoint( 0,0,10);
b2 << IntPoint(10,0,0) << IntPoint(15,0,0) << IntPoint(15,0,10) << IntPoint(10,0,10);
Clipper c2;
c2.AddPath(a2, ptSubject, true);
c2.AddPath(b2, ptClip, true);
Paths solution2;
c2.Execute(ctUnion, solution2, pftNonZero, pftNonZero);
cout << endl;
for (IntPoint ip : solution2[0]) cout << ip.X << ", " << ip.Y << ", " << ip.Z << endl;

In this case the solution is empty.

Should I avoid using 3d values and project evey polygon onto a 2d surface instead?

[Timo Kähkönen]

José Luis Esteban: You may have misunderstood the meaning of Z. It is not Z dimension like in 3D. Z is used to maintain relation between input and output vertices. More information about Z member:
http://www.angusj.com/delphi/clipper/documentation/Docs/Units/ClipperLib/Classes/Clipper/Properties/ZFillFunction.htm

It should be eg. R (relation) instead of Z, which is confusing because Z is used as dimension in 3D programs.

[José Luis Esteban]

You are right. I read http://www.angusj.com/delphi/clipper/documentation/Docs/Units/ClipperLib/PreProcessor/Defines.htm and I understood polygons in 3d could be used.

Thank you!

[Angus Johnson]

It should be eg. R (relation) instead of Z, which is confusing because Z is used as dimension in 3D programs.

Yes, I can see that Z is confusing and I'm considering changing it to U (user defined).