Geometry Boost List: [ggl] Polygon DP simplification

Subject: [ggl] Polygon DP simplification
From: Mateusz Loskot (mateusz)
Date: 2011-09-29 18:53:05

On 28/09/11 18:13, Mateusz Loskot wrote:
> On 27/09/11 21:24, V D wrote:
>> Basically, the original polygon has values between 0 and 1, and is
>> simplified with 1.0/2048.0
>> The second polygon is the original with point values multiplied by 2047
>> (0..2047, so 2048 pixels for example) and is simplified with 1.0
>>
>> Original polygon has 37 points, simplified with 1.0/2048 I get 20 points
>> Multiplied by 2047 and simplified with 1.0, I get 35 points (correct
>> behavior with 1 pixel distance).
>>
>> Shouldn't the number of points of the simplified polygons be the same if
>> the point coordinates and max distance are proportional ?
>
> I confirm there is a problem indeed.
> I quickly checked and I think there is a bug in distance calculation.
> Simply, pythagorean distance calculation is not hooking sqrt.
> I managed to solve it, but in spite of that the solution is technically
> trivial, it potentially affects other areas. It causes number of unit
> test failures, etc.
>
> So, I decided to not to commit it to the trunk, but I submitted ticket
> with patch attached;
>
> https://svn.boost.org/trac/boost/ticket/5954
>
> Can you apply the patch and see if it solves the problem for you?
> My tests (also comparing with results from other geometry libs)
> confirm it should solve the problem.

Here is my result:

https://gist.github.com/1248534

-- 
Mateusz Loskot, http://mateusz.loskot.net
Charter Member of OSGeo, http://osgeo.org
Member of ACCU, http://accu.org