Hi,

Hunk wrote On 22-10-2013 11:40:

Hello

I have two areas which you can see on the follow picture

<http://boost-geometry.203548.n3.nabble.com/file/n4025672/union_.png> 

As Points 

Blue:   
2.5 , 4 / 2.5 , 1 / 2 , 1 / 2 , 4 / 0,4 / 0,0 / 7,0 / 7,5 / 2,5 / 2 , 4
red:
2, 5 / 0 , 5 / 0 , 4 / 2,  4

i expect as solution the outside area 
0,0 7,0 7,4 0 ,4
and the obstacle inside

but the output polygon vector has only the size 1

0,4 / 0,0 / 7,0 /7,5 /0,5

but i dont understand why ...

is the problem the touch point(2,4) on polygon blue?

Nope, the problem is somewhere in your code. I don't see your code so I cannot see what it is, but probably your polygon-definitions (CCW/CCW, Open/Closed) do not correspond to the input you specify. You can always call "correct".

This code works for me:
    boost::geometry::read_wkt("POLYGON((2.5 4 , 2.5   1 , 2   1 , 2   4 , 0 4 , 0 0 , 7 0 , 7 5 , 2 5 , 2 4, 2.5 4))", green);
    boost::geometry::read_wkt("POLYGON((2 5 , 0   5 , 0   4 , 2   4))", blue);

    boost::geometry::correct(green);
    boost::geometry::correct(blue);

and delivers:

The orange line is the union. Colors are different because I adapted a standard doumentation sample.
http://www.boost.org/doc/libs/1_54_0/libs/geometry/doc/html/geometry/reference/algorithms/union_.html

Another option is (remembering your previous mail about REGISTER_RING) that you consider a ring as a polygon. That is not the case. The ring is a simple geometry without any holes. You can output a union to a ring, but any hole is than (by design) discarded. A ring cannot have holes, by definition.

Regards, Barend