Geometry Boost List: [ggl] Polygon DP simplification

Subject: [ggl] Polygon DP simplification
From: V D (zedxz2)
Date: 2011-10-06 22:16:22

Hi Barend,

Thanks for looking at this. 

I will either square my distance or use the projected point distance strategy until the next Boost release that addresses this.
Were you also able to look at the compile problems when trying to specify the pythagoras strategy to DP?

Thanks,
-V

On Oct 6, 2011, at 3:13 PM, Barend Gehrels wrote:

> Hi,
> 
> On 30-9-2011 12:34, Mateusz Loskot wrote:
>> On 30/09/11 11:32, Bruno Lalande wrote:
>>> I don't remember about the details but I'm pretty sure this sqrt was
>>> absent on purpose. It was pulled away from the actual calculation to
>>> avoid useless square root computations when comparing distances, and it
>>> is the responsibility of the caller to call sqrt.
>> 
>> Bruno,
>> 
>> Yes, it makes perfect sense to me.
>> 
>>> So probably one of the
>>> algorithms/operations used fails to do it, we will have to identify
>>> which one. I assume adding the sqrt within pythagoras itself causes all
>>> the operations that use it properly to fail unit tests.
>> 
>> Indeed, that's why I didn't decide to commit it. The patch is fragile.
>> 
>>> I guess Barend will have more details about the actual implementation.
> 
> There is indeed a problem there, which must have been slipped through during rework of the distance strategy. Sorry for that. Because the unit tests test with a distance of 1.0 it went unnoticed. It is provisonally fixed now, such that it gives the correct results and I added a unit test of the case of V D to avoid future regressions. The fix is provisonally because it now calls sqrt in all comparisons, and indeed it was intended to not do that. So I will work on this but don't know if this will be in 1.48. Anyway, it now gives the correct results.
> 
> It (it is actually a one line change) is commited in the Trunk.
> 
> Thanks for the report and the feedback.
> 
> Regards, Barend
> 
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