Geometry Boost List: [ggl] Difference / xor for multi polygons

Subject: [ggl] Difference / xor for multi polygons
From: Barend Gehrels (barend)
Date: 2011-03-06 05:24:05

Hi Javier,

Thanks for testing again.

On 6-3-2011 0:53, Javier Gonzalez wrote:
> Ok, I have good news and bad news.
> The good news is that such test case now works properly :)

:-)

> The bad ones is that I found another faulty test case, this time with 
> UNION.
>

I cannot reproduce this one (my testcode here: 
http://codepad.org/yRHniT9J <http://codepad.org/LmamZ5s9> ) . I closed 
the polygons manually but that makes no difference for me. It gives me 
two rings, an outer ring and an inner ring. This is the output (not in 
codepad):

(green: p1, blue: p2, orange: output including inner ring)

area: 80456.5
wkt:
POLYGON((-2 2,2002 2,2002 -2002,-2 -2002,-2 2) , (0 -182,0 -2000,2000 
-2000,2000 0,104 0,440 -240,400.002 -279.998,400.01 -280,400 -280,359.99 
-280,359.99 -280,0 -182))
>
>
> And once more using the multipolygon version of the union even though 
> the inputs are single polygons (if that matters)

That should not differ. I tried single polygon input only.

>
> I hope I didn't make a typo, that's some amount of numbers...

If possible, please report me a WKT (see code from codepad) for errors, 
that avoids typo's and is convenient to read and write.

One thing, I made an additional fix yesterday, after sending my mail. My 
testprograms found something for counterclockwise direction. It might be 
that this influences the behaviour of this case to. So please update 
again from the Trunk...

I'm still working on a case in difference, having multiple 
self-tangencies. I'm not announcing every commit to this list because 
there are many per day.

Again, thanks for testing and I really appreciate this. I've hundreds of 
tests, including 5 random tests, and with help of that I'm testing 
millions of cases, but apparently there can still slip things through. 
As far as I know union and intersection are completely running for all 
combinations of rings,polygons,multipolygons and for self-tangencies, 
open rings, closed rings, clockwise and counterclockwise, as requested 
in the review report. I hope to solve the self-tangencies in difference 
soon.

Regards, Barend

-- 
Barend Gehrels
http://about.me/barendgehrels
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