[postgis-users] PostGIS Raster for Met Data

[Pierre Racine]

> ----- 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