"wacampbell" <nomail@nomail> wrote:
> I also use this technique ( alpha images on billboards ) and have run into
> this problem with fog.
>
> Try using the 'hollow' keyword on your billboard object.  In my case, for
> billboards formed from a simple 2 triangle mesh, use of the 'hollow'
> keyword solved the problem.
>
>
> Wayne

Thanks a lot Wayne !

Unfortunately, in my case his hollow statement did not change the result,
the transparent area through the fog still become translucent with the
fog's color ;-(

But using a mesh rather than a box make the problem less obvious (may be
because the mesh has just ONE surface while the box has two ?)

However thanks for the idea using the mesh. May be I will simply define the
roof slopes and chimneys in the mesh ?...

Or may be I simply did not use the hollow keyword properly ?

Here is the object

        mesh {
    /* top side */
    triangle {
      <0,0,0>, <1,0,0>, <0,1,0>
      //texture { Red }
    }
    triangle {
      <1,0,0>, <0,1,0>, <1,1,0>
      //texture { Red }
    }

        texture {

                            pigment {
                              image_map {gif "facades71gtr192d.gif"
transmit    192, 1.00
                              }

                            }
                            finish
                         {
                            ambient 0.25
                            diffuse 0.78

                         }
                 }

        scale <390,802,10>*1.45
        rotate y*3
        translate 2 * x* 390 *1.45
        hollow
        }

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