[gdal-dev] Recommended process for running a intersect test between a raster and a simple vector

Andrew C Aitchison andrew at aitchison.me.uk
Wed Jan 15 04:45:55 PST 2020

On Mon, 13 Jan 2020, Brian wrote:

> So I am not sure if this is the right place or not. Feel free to remove if
> it is not.
> The problem:  I am needing to see if an extent (vector polygon, 4 vertices)
> has any interaction with a raster stored in the cog format.
> I thought about using raster_polygonize and running a intersect but that is
> going to be way too slow and I don't need the detail at which the raster is
> stored in.
> So I was thinking of some alternatives.
> Is there anyway to output just the polygon of the raster at a certain
> overview level?
> Is there any way to run intersects on a raster without converting it?

If the data set has tiles or the driver otherwise knows where it has data
and nodata and supports it, the IGetDataCoverageStatus virtual method
may be useful. It takes as input a window of interest and returns whether
it is made of data, empty blocks or a mix of them.

> I know I can retrieve the extent of the raster and quickly determine if an
> extent has any interaction with that raster extent. I also know that I can
> send points(x,y) and retrieve the value of the raster at that point is
> there any way to manipulate /game this? Maybe sending the extent as
> individual points with added points in between the vertices and just
> running multiple value at location operations? For my need, some false
> positives would be acceptable. If it helps raster data is of rivers and
> inundations.

Andrew C. Aitchison					Kendal, UK
 			andrew at aitchison.me.uk

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