[gdal-dev] ogr2ogr -makevalid [was Re: Algorithm to clip the inner loop of a polygon]

[Even Rouault]

Chao YUE,

This is probably not exactly what you want, but I wanted to mention that ogr2ogr in latest 
GDAL master has now received a -makevalid switch that relies on GEOSMakeValid() method 
of GEOS 3.8.0 or later (which itself is the port of PostGIS ST_MakeValid() to GEOS).

For people using the SQL SQLite dialect, ST_MakeValid() is also now available (still with GEOS 
>= 3.8), even against a Spatialite build that doesn't link against liblwgeom

Even

> Dear all,
> 
> Does anyone have some experience or is aware of some algorithm that can
> find and clip the inner loop formed in a polygon ? I attach one example
> here. In this case I would only keep the outer points and drop the ones
> that make an inner loop. I am developing some algorithm to simulate
> wildland fire propagation. The algorithm is based on Richards 1990.
> 
> In the paper he described an algorithm based on two steps: (1) find the
> points where a concave curvature is made. (2) search for both sides of this
> point to see where any two line segments cross over each other.
> But I am wondering whether there is already some existing solutions or
> other better ones.
> 
> Thanks a lot for the kind help for any hints on this !
> Kind regards,
> Chao
> 
> Gwynfor Richards, 1990. An elliptical growth model of forest fire fronts
> and its numerical solution. International journal for Numerical Methods in
> Engineering, Vol. 30, 1163-1179.
> 
> [image: InnerLoop.png]


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