Geometry Boost List: [ggl] Within polygon detection including the polygon borders

Subject: [ggl] Within polygon detection including the polygon borders
From: Barend Gehrels (Barend.Gehrels)
Date: 2009-09-21 05:56:51

Hi Ivan, Bruno,

I've looked to your example and the results seem very strange indeed. 
There are two errors, one in the testprogram, one in the library 
(preview 4).

1) In the testprogram: the polygon is not defined correctly: {100.0, 
100.0}, {200.0, 200.0}, {100.0, 200.0}, {200.0, 100.0}, {100.0, 100.0} 

the polygon starts at lowerleft, goes to upper-right, then to 
upper-left, then to lower-right, then closes. The code before
    ggl::point_2d c3 = make<point_2d>(100,100);
      ggl::point_2d c4 = make<point_2d>(100,200);
      ggl::point_2d c5 = make<point_2d>(200,200);
      ggl::point_2d c6 = make<point_2d>(200,100);
      ggl::point_2d c7 = make<point_2d>(100,100);
was correct and as intended, but that code is not used (anymore)

Therefore the centroid point also gives a strange value (0, 1e+006).

2) In the library (preview 4): the results are still wrong indeed, using 
preview 4. Using the head (hosted at Geodan SVN) it is OK. The code in 
preview4 didn't handle points on segments correctly, this was solved in 
the meantime. So I updated preview 4, hosted at Boost SVN, with the new 
code and it is OK now.

Ivan, note that you can also have SVN access to the Geodan SVN, you're 
working then with the newest versions, up for Boost preview or review 
next month, if this is feasable.

Regards, Barend

Ivan Marin wrote:
> Hello Mr. Barends,
>
> 2009/9/18 Barend Gehrels <Barend.Gehrels_at_[hidden] 
> <mailto:Barend.Gehrels_at_[hidden]>>
>
>     Hi Ivan,
>
>     Sorry for my very late reaction. I was on holiday from Sep 3 on.
>
>
>
>
>         I successfully compiled the examples
>
>     Does this mean I can ignore your other question of Sep 3?
>
>
> I was able to compile the examples, but what I did was kind of a hack: 
> I've just copied the directory geometry to /usr/include. Putting it on 
> the local directory or inside the boost directory did not work, and I 
> was puzzled by that. But it is working.
>  
>
>
>
>         and now I'm trying to use the ggl. I need to check if a point
>         is inside a polygon, and I want to consider de borders as part
>         of the polygon. Is this possible in ggl? All the tests that
>         I've made showed me that this is not possible.
>
>     That is right, currently it is not possible. We will have another
>     function which can be used for this question. It will either be an
>     option of "within", or it you could use the "distance" function on
>     point-polygon, which is zero or if the polygon is on the border or
>     inside. Actually the last one can also be discussed, if the point
>     is inside the polygon, it could be less than zero or also as an
>     option.
>
>
> Ok, I see. Now I've developed my theory that if I can say if the point 
> is just inside the polygon will suffice. The problem now that I was 
> discussing with Bruno is that there is a case where the routine within 
> is not working properly: if I define a polygon with vertices 100 100, 
> 200 100, 200 200, 100 200, and search for all the points inside the 
> polygon, the routine outputs points that are not inside the polygon as 
> inside. Bruno was able to reproduce this bug. I attached the code that 
> I used to produce this problem. Is there a proper place to submit a 
> bug report, or is any more data needed? I'm willing to help, and if 
> possible, even debug.
>  
>
>
>     But both are currently not implemented.
>
>
>
> Thank you very much!
>
> Best regards,
>
> Ivan Marin
> Laborat?rio de Hidr?ulica Computacional - Computational Hydraulics Lab 
> - LHC
> Depto de Hidr?ulica e Saneamento - Sanitation and Hydraulics Dept.
> Escola de Engenharia de S?o Carlos - Universidade de S?o Paulo - EESC 
> - USP
>  
>
>
>
>     Best regards,
>     Barend Gehrels
>     Geodan, Amsterdam
>
>
>
>
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-- 
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Barend Gehrels
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