Re: GSOC Project "Implement boolean operations on polygons" GNU Octave

[Philip Nienhuis]

John Swensen-3 wrote
>> On Mar 15, 2016, at 3:10 AM, PhilipNienhuis <

> pr.nienhuis@

> > wrote:
>> 
>> Juan Pablo Carbajal-2 wrote
>>> On Mon, Mar 14, 2016 at 4:10 PM, Albu Mihai <
>> 
>>> albumihaiupb@
>> 
>>> > wrote:
>>>> Hello,
>>>> 
>>>> My name is Albu Mihai and I am a student at University Politehnica of
>>>> Bucharest, more exactly at Computers and Information Technology. I want
>>>> to
>>>> work at Google Summer of Code 2016 and I chosed you because I like
>>>> mathematics and I saw an interesting project you have there, the one
>>>> with
>>>> polygons operations. The proposal I have is to do a dynamic list with
>>>> the
>>>> coords of points that creates the polygons and we use mathematic
>>>> functions
>>>> to know how are the polygons defined. In this way, we can do easy the
>>>> operations.
>>>> 
>>>> 
>>> 
>>> Hello Albu,
>>> 
>>> That's great. Read the instructions on the wiki page, and start
>>> coding. If you have questions just ask here on in the IRC channel. Do
>>> not forget to write your application for GSoC on due time.
>> 
>> In order to avoid reinventing the wheel it may be wise to first check
>> what
>> is already available out there and use proven solutions as much as
>> possible.
>> 
>> A while ago in this mailing list some suggestions were mentioned.
>> 
>> Philip
>> 
> 
> 
> I would recommend you take a look at a couple of the different existing
> polygon boolean libraries available. The project ideas page
> (http://wiki.octave.org/Summer_of_Code_Project_Ideas
> <http://wiki.octave.org/Summer_of_Code_Project_Ideas>) has links to
> four different solutions with compatible licenses (ClipperLib,
> Boost::Polygon, Boost::Geometry, and KBool) and a link to a partial Octave
> implementation using ClipperLib. 
> 
> I agree with Philip that using an existing solution would make it possible
> to start tackling the problem of integration with Octave, rather than
> working on polygon point representations. As far as I know, all of these
> libraries use the convention of alternating winding direction (clockwise
> or counter clockwise) to indicate whether the points represent an outer
> polygon boundary or and inner hole boundary.

Last summer I stumbled upon a comparison of various polygon clipping
libraries (5 or 6 IIRC) by a Russian (?) guy which outlined that only 2 or 3
could handle holes. (Too bad I can't find that URL anymore.) kBool and
(IIRC) boost were among those that could handle holes in polygons (+ of
course GPC but that has an incompatible license).

IIRC one of those (clipper IIRC) used integer coordinates rather than
float/double. I had it working (I remember vaguely something with a MEX
file) but that coordinate translation didn't work in the end because of
required coordinate transforms (for GIS shapefiles with real-world
coordinates) and back each time depending on the coordinate ranges at hand.
>From what I remember that became a headache and I intended to switch to
kbool/boolean but then I ran out of time.

Philip




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