[postgis-tickets] [PostGIS] #5311: ST_Contour bug over the limits of tiles

[PostGIS]

#5311: ST_Contour bug over the limits of tiles
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  Reporter:  latot   |      Owner:  robe
      Type:  defect  |     Status:  new
  Priority:  medium  |  Milestone:  PostGIS 3.3.3
 Component:  raster  |    Version:  3.3.x
Resolution:          |   Keywords:
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Comment (by latot):

 mm, personally is weird the bug it self....

 When we store a raster in a db, we expect to be able to access to any
 pixel in a similar way, there should be only one raster from the "out"
 perspective, even if is decided to save the raster as several tiles, all
 the raster funcs should run over all the data, so when we run a function
 that works for example, in the nearest pixels, will run fine in all of
 them, including in the limit of the tiles (there maybe must be some
 constraints).

 I don't think the idea should be "trick" postgis in order to get
 algorithms to work, we use postgis because is able to handle big amounts
 of spatial data and we have good access and functions.

 GDAL devs tell me a little about this, is in fact similar, in order to get
 contours or apply any other function we should use vrt format, vrt is not
 a "raster" format like tiff, it just tell to GDAL where the tiff files
 are, and insure access too all pixels like one big raster, this is usually
 what we can expect from postgis, very similar. I tested it and works
 great. The only thing I didn't tested is in case two rasters overlap.

 I'm just a little worried about:
 This is not something that is/will be changed/fixed in PostGIS.

 If, for the contour function, the access to the pixels can't be insured in
 a uniform way for the function, maybe for other functions can happens too.
 Maybe you know, when and how this can happens, but for the ones who didn't
 read and know that much detail that is insternal to postgis, I think is a
 fair thought.

 The actual contour function, without this fix is mainly broken. Think in
 the usual 100x100 tiles, so you will probably have more than 1 tile, we
 load a super raster, run contour, and ppl will think will works fine while
 is not the case... D:

 Just as note, and avoid misunderstandings, the bug here is the lines are
 not connected betwen the tiles, so the contours are broken.

 Sorry if I was too brute in my explanation, if I misunderstood something
 sorry too!
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Ticket URL: <https://trac.osgeo.org/postgis/ticket/5311#comment:4>
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