[GRASS-dev] [GRASS GIS] #2282: r.external.out: keep GRASS maps and external files in sync

[GRASS GIS]

#2282: r.external.out: keep GRASS maps and external files in sync
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 Reporter:  sbl          |       Owner:  grass-dev@…              
     Type:  enhancement  |      Status:  new                      
 Priority:  normal       |   Milestone:  7.1.0                    
Component:  Default      |     Version:  unspecified              
 Keywords:               |    Platform:  Unspecified              
      Cpu:  Unspecified  |  
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Comment(by glynn):

 Replying to [comment:2 sbl]:

 > 1) Let`s say a user sets the external output path to ~/output for
 GeoTiffs with extension ."tif". Then the user produces a map with the name
 "map_a". Later this "map_a" is renamed to "map_b". The file
 "~/output/map_a.tif" will then be linked to "map_b", right? What happens
 in such a case, if another map with the name "map_a" is produced. The map
 name does not exist anymore in GRASS, but the file "~/output/map_a.tif"
 does, on the file system. Is it checked that "~/output/map_a.tif" is not
 overwritten in such a case.

 I don't think so. Not unless GDALCreate() performs such a check.

 It's awkward for GRASS to do it, because the "filename" (i.e. dataset
 name) might not actually correspond to a file (although I'm not sure that
 the code correctly handles non-file datasets at present).

 > 2) Let`s assume one wants to use maps produced in GRASS with
 r.external.out in other software. During map production the user finds
 out, that a different name for the map would have been more suitable.
 After running g.rename the new, more appropriate name is used in GRASS
 while other software will still have to work with the old filename. The
 way to sync that manually would be to remove the map (link) (instead of
 renaming it), rename the underlying file (mv), and then link that file
 again into GRASS (r.external). What happens to map history in such cases?

 Removing the GRASS map (with g.remove) will remove any metadata which
 isn't part of the underlying GDAL dataset (e.g. image file).

 Currently, the only metadata GRASS stores in the file is the region
 (bounds and resolution). The code is there to store the projection (SRS),
 but that information isn't available at present (we'd need to move
 GPJ_grass_to_wkt() etc from libgproj into libgis, which would make GDAL a
 direct dependency of libgis).

 > In general, I think having an option for keeping maps and files in sync
 automatically would make it much more easy to maintain a tidy and clean
 data storage with external files...

 Probably. The main issue is whether it's feasible to modify the existing
 management tools (g.rename etc) to handle this, or whether we need
 specific tools related to GDAL-linked (r.external) maps. I suspect that
 most of these issues would also apply to OGR-linked (v.external) vector
 maps.

 BTW, there would also be the issue of how to handle filenames which aren't
 valid map names (as per G_legal_filename()), e.g. those containing spaces.
 Or map names which aren't valid filenames (GRASS allows :?|<> in map
 names, but Windows doesn't allow those characters in filenames).

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Ticket URL: <http://trac.osgeo.org/grass/ticket/2282#comment:3>
GRASS GIS <http://grass.osgeo.org>