[gdal-dev] Open source API to convert raster to polygons?

[Ari Jolma]

Joaquim Luis kirjoitti:
> Ari Jolma wrote:
>>
>> I've written a raster to polygon converter, which produces closed 
>> polygons from raster images.
>
> Hi,
> I am sorry but I have some difficulties in understanding this discussion.
> What is a raster to polygon conversion?
> I know, and have played with, vectorizing edge detected images, shape 
> detection of simple forms like ellipses, lines, ridge crests on DTMs 
> etc...
> but for each of these goals the tools/algorithms used are different. 
> What I do not understand is what is a generic "raster to polygon 
> conversion".

The raster to vector converter I've written is a tool that is based on 
an algorithm that you would apply after some kind of edge detection, 
posterize, classification, etc. tool. The algorithm works on integer 
pixel values and two pixels belong to an area if they have the same 
integer value. In my case I needed it for some work with classified land 
cover images, which have by nature only few pixel values.

The contour line algorithm in GDAL is different in the sense that it 
works on DEMs and it does not assume integer values and draws the lines 
through locations it finds using linear interpolation.

Cheers,

Ari

-- 
Prof. Ari Jolma
Geoinformatiikka / Geoinformatics
Teknillinen Korkeakoulu / Helsinki University of Technology
tel: +358 9 451 3886 address: POBox 1200, 02015 TKK, Finland
Email: ari.jolma at tkk.fi URL: http://www.tkk.fi/~jolma