Hi,
I believe that this is totally grey are in WCS 1.0.0 but for WCS 2.0 there
seems to be two papers which are not official standards but maybe sort of
recommendations:
https://portal.opengeospatial.org/files/?artifact_id=51141
https://portal.opengeospatial.org/files/?artifact_id=51142
From the first one you can read that both pixel is area and pixel is point are
supported if GeoTIFF coverages:
Requirement 9 /req/geotiff-coverage/pixel-is-area: The domain of a coverage
using GeoTIFF encoding shall respect the coverage’s raster space as defined in
the GeoTIFF specification [GeoTIFF] i.e. in PixelIsArea the first pixel-value
fills the square grid cell with the bounds top-left = (0,0), bottom-right =
(1,1) and in PixelIsPoint the first pixel-value is realized as a point value
located at (0,0).
I recommend to read the whole document but according to this excerpt the
georeferencing info that is written as a rectified grid in GML will be slightly
different for PixelIsArea and PixelIsPoint. The origin and offsetVectors are
the same but the BoundedBy area is half a pixel wider to all directions for
PixelIsArea than for PixelIsPoint.
Note The definition of grids in GML 3.2 [OGC 07-036] clause 19.2.2 which GMLCOV
is based on reads as: “When a grid point is used to represent a sample space
(e.g. image pixel), the grid point represents the center of the sample space
(see ISO 19123:2005, 8.2.2).”. Image pixel in this GML quote denotes the same
as image space in GeoTIFF terminology. In a gml:RectifiedGrid used with
PixelIsArea this applies to the gml:origin element which is therefore shifted
by half a gml:offsetVector in both dimensions compared to the gml:boundedBy
element.
Note GMLCOV does not store the raster type i.e. PixelIsArea or PixelIsPoint
information in its current version. However, Requirement 9 above specifies that
the gml:boundedBy element shall respect the raster type i.e. it shall include
the half pixel border in case of PixelIsArea (see also Figure 1).
-Jukka Rahkonen-
Andrea Aime wrote:
Hi Andrew,
in geotools we call this issue "pixel is center" vs " pixel is corner".
OGC mandates the "pixel is center" interpretation as far as I know, see also:
http://gis.stackexchange.com/questions/122670/is-there-a-standard-for-the-coordinates-of-pixels-in-georeferenced-rasters
http://mapserver.org/fr/development/rfc/ms-rfc-107.html
As far as I know, GeoTools tries to work "pixel is center" from beginning to
end, and there
are no ways to control that, also, WCS follows the OGC interpretation strictly
and does not
offer a way to return "pixel is corner" rasters, but I may be wrong.
I'm cc'ing Daniele, he should know more on this matter.
That said, especially in WCS 2.0, built to be extensible, one could put
together a vendor profile that allows controlling
the pixel interpretation for the outputs.
Cheers
Andrea
On Tue, Mar 31, 2015 at 11:28 PM, Andrew Annex
<aan...@ccri.com<mailto:aan...@ccri.com>> wrote:
Hello GeoServer users,
I am making wcs 1.0.0 requests for geotiffs against a coverage layer.
Does GeoServer support returning geotiffs via wcs that are "Point"
instead of "Area" pixels for the meta-data value: "AREA_OR_POINT"? This
metadata field is further explained here:
http://www.gdal.org/gdal_datamodel.html. By default the geotiff writer
assumes area, and that writer appears to be used in the
GeoTIFFCoverageResponseDelegate. Is there some way to set this as a hint
in the wcs query url or is there something I can overwrite when
extending the AbstractGridCoverage2DReader and/or the AbstractGridFormat
so that the ResponseDelegate will pick up on that hint? Although it may
not matter I am working with geoserver 2.5.2 / geotools 11.2.
Also if this question is more appropriate for the geotools user list let
me know.
Thanks - Andrew
--
- Andrew Annex, Data Scientist.
- (434)-284-9405 ext. 153<tel:%28434%29-284-9405%20ext.%20153>
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