OGC WCS and TIME

[Ara T Howard]

On Wed, 20 Dec 2006, Norman Barker wrote:

hi norman-

> I have done this a lot :-), what type of datasets are you trying to use?
> Python with GDAL, OGR makes this very easy.
>
> For an example I have pasted a python script that creates U+V shape indexes
> for MapServer WCS.  It prints the times out at the end which you can copy in
> the mapfile as per the shape file.
>
> Let me know if you need any help.
>
> Norman

<snip> python script which i'm reading now </snip>

we will be serving dmsp (http://www.ngdc.noaa.gov/dmsp/) global mosaics
imagery of both visible and thermal bands
(http://www.ngdc.noaa.gov/eog/nrt/html/mosaic/ut_night/loop/).

we'll be serving one mosaic per band (5x) per satellite (2-3) per utday.  we
aim to have 30-90 days on disk and that leads to something like a max of 1000
layers.  our mapserver is compiled with MS_MAXLAYERS=200 and we could simply
boost - but that's getting to be a BIG mapfile!  i looked at using dynamic
layters but, afaikt, adding layers dynamically via mapscript results in fubar
DescribeCoverage calls (see recent un-answered thread started by me on the
subject).

therefore, what i'm trying to do is to uses mapserver's tiling support with
the TIME= filter to store one utday's mosaic per tile and then, obviously, to
require TIME=utday in the query.  ultimately i plan to have band and satellite
specifc tiles as well to use with BAND= and PARAMETER= query components.  note
that none of our tiles are acutal spatial diviions.  we'd like to use spatial
tiles but research so far shows consistent projection errors when spatially
tiled imagery is served.

so, in summary, step one is reduce the number of layers i have by creating
custom shapefiles (i fear this is the only way) which will support/require
a TIME= component in each request.  the time component with by at the utday
granularity.  an example tile name is

   F1520061212.nt.d.OIS.vis.mos.tif
      ^^^^^^^^
      ^^^^^^^^
      ^^^^^^^^
      utday

my specific (newbie) questions are

   1) how to create custom shapefiles which would included a time index.  i think
   i'll be able to manage this with your example python script and by examining
   the output of gdaltindex.  i'm using ruby btw ;-) !

   2) how to configure a mapfile to reflect this change in structure.  a vis
   layer is now specified in auto-generated mapfiles this way:

     LAYER
       NAME "F1620061220.nt.d.OIS.vis.mos.tif"
       PROCESSING "SCALE_1=0,63"
       METADATA
         wcs_description "F1620061220.nt.d.OIS.vis.mos.tif"
         wcs_name "F1620061220.nt.d.OIS.vis.mos.tif"
         wcs_label "F1620061220.nt.d.OIS.vis.mos.tif"
         ows_srs "EPSG:4326"
         ows_extent "-180 -75 180 75"
         wcs_resolution "0.00833333 -0.00833333"
         wcs_bandcount "1"
         wcs_formats "GEOTIFF"
         wcs_nativeformat "8-bit GeoTIF"
         wcs_rangeset_name "F1620061220.nt.d.OIS.vis.mos.tif"
         wcs_rangeset_label "vis"
         wcs_rangeset_axes "bands"
         wcs_bands_name "bands"
         wcs_bands_semantic "http://www.ngdc.noaa.gov/dmsp/"
         wcs_bands_refSys "European Petroleum Survey Group (EPSG)"
         wcs_bands_label "F1620061220.nt.d.OIS.vis.mos.tif"
         wcs_bands_values "VIS"
       END
       STATUS off
       DUMP true
       DATA "F1620061220.nt.d.OIS.vis.mos.tif"
       TYPE raster
       PROJECTION
         "init=epsg:4326"
       END
     END

   i realize i'll have to add an index layer and to refer to it somehow in
   another layer definition, but am not quite clear how to go about this.

   3) how much further i can abuse tile support to reduce the number of layers
   in my mapfile.  i'm fairly certain band specfic tiles can be made to work
   using BAND= query component, but am uncertain of PARAMETER= could be used to
   support arbitrary, in this case by satellite, tiling.

   4) assuming the issues with data projection can be solved, if spatial tiling
   could also be layered on top of the above later.


   5) ... just kidding - i suppose that's enough questions for now!


thanks for the input!

kind regards.

-a
-- 
if you find yourself slandering anybody, first imagine that your mouth is
filled with excrement.  it will break you of the habit quickly enough. - the
dalai lama