[gdal-dev] gdal contour, output polygon

[ValiSystem]

Hello !

I'm trying to generate polygons from gdal contour output. Most of the 
linestrings generated where closed, so it's not a too bad start. The 
problem is to define interior and exterior of the polygon : it seems 
that interior and exterior has no consistent meaning from the 
linestrings (it makes sense though - a line has no interior nor than 
exterior).

So what i need would be a method to recreate the meaning of the polygon 
: the inside is where i have ground. To make it work, i just would have 
to transform the polygon to an interior ring of a wider (whole area) 
polygon when appropriate (when it does not contain a polygon with a 
higher altitude).

What do you think about this ? is there a better/known way to achieve that ?