[postgis-devel] [PostGIS] #497: [raster] Start testing displaying PostGIS raster with Mapserver

[PostGIS]

#497: [raster] Start testing displaying PostGIS raster with Mapserver
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 Reporter:  robe            |       Owner:  robe         
     Type:  task            |      Status:  new          
 Priority:  medium          |   Milestone:  PostGIS 2.0.0
Component:  postgis raster  |     Version:  trunk        
 Keywords:                  |  
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Comment(by jorgearevalo):

 We're mixing 2 different queries here:

 The metadata query is only used when creating the GDALDataset object,
 before querying for any data block. Just to inform GDAL about the
 properties of the raster. With "mode = 2", the driver expect 1 table = 1
 raster coverage = 1 GDALDataset object, and it needs to know some things
 about the raster, like georreference (of the WHOLE coverage, not only 1
 row), extent, srid (again, of the whole coverage). For this reason, I
 execute a query to fetch the metadata of all rows. I could limit the query
 to 1 result, like you said, but we have a problem here:

 > If I use mode='2' I was assuming that meant to create one GDALRaster
 dataset and
 > assume that by saying mode='2' I'm basically saying its evenly blocked,
 it has the
 > same srid and there are no overlapping tiles.

 The driver expects that, but if the raster is not evenly blocked, if
 there're rows with different srid... it must do something. For example:
 warn the user and exit, or resample all the rows to the grid of the first
 one, or ask for a new grid alingment.

 Of course, the first option is the easiest one, but the point is the
 driver still needs to know it. It must check if everything is just like
 expected (raster evenly blocked, all tiles with same srid, no overlapping
 tiles). It must get the metadata of all tiles, to check it. Or am I wrong
 with my approach?

 Apart from this, a different query is the query executed when the driver
 really asks for data. No metadata involved in this query. Only x,y offsets
 that must be converted to a specific data block (using georeference
 information and a spatial operator, like &&, or ~). I argue the query I'm
 using is too slow, because implies one server round per readblock call.

 {{{
 SELECT rid, rast FROM aerials.o_2_boston WHERE rast ~
 ST_SETSRID(ST_makebox2d(st_point(225866,892151),
 st_point(225926,892211)),26986);
 }}}

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Ticket URL: <http://trac.osgeo.org/postgis/ticket/497#comment:13>
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