Accessing images using time dimension.

[Yewondwossen Assefa]

Dave Weaver wrote:
> (Apologies if this is a duplicate - I posted on Friday but haven't seen the
> message appear on the list, so I'm trying once again...)
> 
> I'm having some difficulty displaying images using the WMS TIME=
> parameter to select different time periods. I've scoured the
> documentation, and although I get the general idea I don't see any
> document that explains the basic steps needed to get this working (the
> "WMS Time Support" document gives a rough idea, but misses out on some
> of the details), so I suspect I've missed something or got something
> wrong, but I've no idea what!
> 
> This is what I've done:
> 
> * I have done the following in Postgis:
> 
>  create table satellite (image_path text, image_time timestamp);
>  select AddGeometryColumn('satellite', 'the_geom', 4326, 'POLYGON', 2);
>  insert into satellite (image_path, image_time, the_geom) values,
> '/home/map/fgs/www/htdocs/maps/images/sat1.tiff', '2007-05-11 10:00Z',
> null);
>  insert into satellite (image_path, image_time, the_geom) values
> ('/home/map/fgs/www/htdocs/maps/images/sat2.tiff', '2007-05-11
> 11:00Z', null);
> 
> *  My .map file has (amongst others) these layers:
> 
>  LAYER
>    NAME            "time_idx"
>    TYPE            POLYGON
>    STATUS          ON
>    CONNECTIONTYPE  POSTGIS
>    CONNECTION      "dbname=map host=localhost"
>    DATA            "the_geom from satellite using unique oid using srid = 4326"
>    METADATA
>        "wms_title"         "time index"
>        "wms_srs"           "EPSG:4326"
>        "wms_timeextent"    "2007-01-01/2007-12-31"
>        "wms_timeitem"      "image_time" #a column in postgis table of
> type timestamp
>        "wms_timedefault"   "2007-05-11T10:00:00Z"
>    END
>  END
> 
>  LAYER
>    NAME    "sat"
>    METADATA
>        "wms_title"         "Satellite"
>        "wms_srs"           "EPSG:4326"
>        "wms_timeextent"    "2007-01-01/2007-12-31"
>        "wms_timeitem"      "image_time" #a column in postgis table of
> type timestamp
>        "wms_timedefault"   "2007-05-11T10:00:00Z"
>    END
>    STATUS  ON
>    TYPE    RASTER
>    PROJECTION
>      "init=epsg:4326"
>    END
>    TILEINDEX "time_idx"        # Layer name containing time index
>    TILEITEM  "image_path"      # DB column containing path to image
>  END
> 
> * The URL I'm using to access the data is:
> http://localhost:8080/cgi-bin/mapserv?map=/home/map/fgs/www/htdocs/maps/postgis2.map&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&LAYERS=world,sat,radar&WIDTH=800&HEIGHT=400&FORMAT=image/png&TRANSPARENT=false&&BBOX=-90,-25,90,85&TIME=2007-05-11T11:00
> 
> When I use this URL in my browser I see the underlying vector map
> layer, but no satellite image appears.
> 
> So...
> 
> 1) What am I doing wrong (or not doing at all) ?
> 
   Do you have your imagery displaying when doing a simple draw map ?
(either a wms getmap or mapserver cgi). This is to make sure that the
tile index and the pg layers are set properly.

> 2) Am I right in thinking the geometry column can be null and the rows
> will still be considered, depending on image_time ?
> 
  I think the geometry needs to be valid, each row of geometry should 
normally represent the bbox of the image.

> 3) Is the duplication of the metadata in the 2 layers above necessary?
> I've done it this way because that's what's in the example in the "WMS
> Time Support" document, but do I really need to repeat all this
> information?
> 
  The matadata should only be necessary on the tileindex layer.

> 4) How can I debug this - is there some way I can find out *why* it's
> not displaying the raster layer? Is there maybe some way to show which
> time periods it's considering?
> 

   the wms time in your case ends up setting the filter element on your
postgis layer to something like :
"(date_trunc('minute',image_time) = '2007-05-11T11:00:00')" .
  Assuming that your imagery is displayed without a time request,you can
manually set the filter element and see if that is working.

>
> 5) Is there some basic HowTo document that explains what I'm trying to
> do? (I couldn't find one).
> 
> Thanks a lot
> Dave.
> 


-- 
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Assefa Yewondwossen
Software Analyst

Email: assefa at dmsolutions.ca
http://www.dmsolutions.ca/

Phone: (613) 565-5056 (ext 14)
Fax:   (613) 565-0925
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