# [geos-devel] Simplify vs removeRepeatedPoints

Martin Davis mtnclimb at gmail.com
Thu Mar 28 07:59:05 PDT 2019

```CoordinateSequence::removeRepeatedPoints does NOT do what you want - it
only removes consecutive points which have *identical* values.

You can probably use the DP Simplifier to remove redundant point along
straight lines by calling it with a very small distance tolerance.  This
will be a bit brittle however - if there happen to be points along the
square edges which are within that tolerance of a corner then the corner
point might get removed instead.  (For non-rectilinear geometry this
doesn't really matter, but of course for a rectangle it will make it
slightly non-rectilinear)

On Thu, Mar 28, 2019 at 3:51 AM Paul Meems <bontepaarden at gmail.com> wrote:

> I'm looking at geos::simplify::DouglasPeuckerLineSimplifier (
> http://geos.refractions.net/ro/doxygen_docs/html/classgeos_1_1simplify_1_1DouglasPeuckerLineSimplifier.html#_details)
> and  geos::geom::CoordinateSequence::removeRepeatedPoints (
> http://geos.refractions.net/ro/doxygen_docs/html/classgeos_1_1geom_1_1CoordinateSequence.html#a22
> )
>
> Looking at the explanation of the Ramerâ€“Douglasâ€“Peucker algorithm (
> https://en.wikipedia.org/wiki/Ramer%E2%80%93Douglas%E2%80%93Peucker_algorithm)
> I understand that the resulting geometry might be slightly different,
> that's why a tolerance needs to be added.
>
> But I don't want my geometry to be altered I just want to remove vertices
> that don't contribute to the shape of the geometry.
> Consider a square with not only 4 corner points but also points between
> the corner points.
> Those points I want to remove because they are redundant and without them,
> I still have the 'same' square.
>
> Should/can I use removeRepeatedPoints() or should I use another method?
>
> Thanks,
>
> Paul
>
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