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Subject: [ggl] Polygon DP simplification
From: Mateusz Loskot (mateusz)
Date: 2011-09-29 18:50:12

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;

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.

Best regards,

Mateusz Loskot,
Charter Member of OSGeo,
Member of ACCU,

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