Re: [boost] GGL issues - Access Violation

Subject: Re: [boost] GGL issues - Access Violation
From: Brandon Kohn (blkohn_at_[hidden])
Date: 2009-11-18 09:27:40

Barend Gehrels wrote:
> 
>> I wouldn't call this test stressing the library to its limits. This 
>> operation is on two fairly ordinary small scale isovists (visibility 
>> polygons). As for reversed inputs being invalid, this doesn't make 
>> sense in the context that the negation operation creates a reverse of 
>> a polygon. This is how the boolean difference is defined (at least one 
>> way). How do you do the difference operation in GGL?
> This is explained on that web-page I referred to yesterday, and touched 
> in previous discussions with Luke. Summary: it is not yet available as a 
> separate function but the operation itself is supported by the 
> algorithm, we have to walk through the input with iterators, sometimes 
> forward, sometimes reverse.
> 

My question must have confused you. I wasn't asking how the algorithm 
works. I'm asking how you have tested the difference operation, i.e. 
what methods do you call and what are the forms of the inputs? The 
documentation says that difference is supported.

> I cannot yet respond on isovists because it is still being researched.
> 
I wasn't asking you about isovists. I was just telling you how these 
polygons I used were created. They are simple polygons which form 
boundary of the visible area from a source point. Perhaps it's best if 
we don't cloud the issue with worry about isovists. For now let's focus 
on how taking a difference works.

Regards,

Brandon