[postgis-users] PostGIS Raster for Met Data

[Michael Akinde]

Hi,

Thanks for the suggestions. I'm going to try a few experiments with our code, and probably get back to this later.

Regards,

Michael A.

----- Original Message -----
> > ----- Original Message -----
> > > For sure doing overlay gis operations like st_intersection is not
> > > possible when the srid of the two geometries is different. In this
> > > case you would have to reproject (ST_Transform) the geometry so it
> > > fit
> > > the srid of right grid. But if your application is able to decide
> > > which grid it must query then it should also be able to decide
> > > which
> > > tale it must query and hence putting all your grids in different
> > > table
> > > should not be a problem.
> >
> > For the general case (particularly in the coast example, where the
> > queries are
> > basically just Lon/Lat), we would not know which grid contains the
> > answer.
> > Consequently we would have to do two queries (one to determine the
> > grid to
> > query and one to query the specific grid), where today we make do
> > with one. I
> > suspect that this would cost us a fair bit of performance.
> 
> You could have a table of the outlines of each dataset and use CASE to
> determine to which srid reproject your point. All that in one query.
> 
> > > You can easily get the x,y upperleft corner of a pixel with the
> > > Raster2WorldcoordX(0,0) and Raster2WorldcoordY(1,0) functions. Is
> > > that
> > > what you need?
> >
> > Not quite - I was thinking more of World2RasterCoord, but using a
> > geometry to
> > extract multiple raster points. Essentially, ST_INTERSECT, but
> > returning raster
> > coordinates rather than world coordinates and value.
> 
> You can extract every point of a complex geometry using a mixture of
> ST_PointN(),ST_NPoints(),ST_NumGeometries() and ST_GeometryN(). Have a
> look in the PostGIS doc.
> 
> Pierre
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