[gdal-dev] Countour polygons instead of lines

[Vincent Mora]

I think that this could also be done as post-processing step: collapsing
lines that are really close-by a discontinuity on the discontinuity (snap).

I was thinking about using the borders I introduced to close contours
(no data zones and raster edges) to handle those discontinuities, but I
don't think it will look good.

Another think I'd like to explore is contour simplification to avoid the
huge number of points caused by the marching squares. I'm well aware of
the complexity of the problem, but it's an interesting one ;-)


Le 22/10/2017 à 15:06, Roberto Ribeiro a écrit :
> In cases of cliffs and such (i.e. sudden drops in altitude),
> traditional photogrammetric softwares like PCI and Erdas work with
> break lines, as in, you literally draw a line along edges you want
> computed discontinuously. That is not really practical to do in
> command-line GDAL, though you could import a previously created line
> vector and tell the algorithm to process with those in mind.
>
> 2017-10-20 16:18 GMT-02:00 Andrew C Aitchison <andrew at aitchison.me.uk
> <mailto:andrew at aitchison.me.uk>>:
>
>     On Fri, 20 Oct 2017, Vincent Mora wrote:
>
>         I'll also try the gdal_polygonize approach, but I don't think
>         it's the
>         same thingl: with raster-classif + gdal_polygonize, if you have 3
>         classes 1,2,3 polygons from 1 can touch a polygon from 3, with
>         contour
>         lines there will always be a polygon of class 2 in between.
>
>         Or am I missing something.
>
>         If someone believes I'm doing something useless and/or stupid
>         (that also
>         happens), please do tell.
>
>
>     Can you polygonize contours across a vertical cliff ?
>     If so, 2 may be "between" 1 and 3, but at some points they may all
>     touch.
>
>     On some maps, contours become discontinuous around cliffs and
>     quarries.
>
>     -- 
>     Andrew C Aitchison
>
>
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