| Re: Projected Image Data [message #29525] |
Thu, 28 February 2002 00:31 |
Vincent Schut
Messages: 8
Registered: February 2002
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Junior Member |
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David Fanning wrote:
> Folks,
>
> Do any of you netCDF-types know of any "standards"
> regarding how to store already-projected satellite image
> data in netCDF files? Are lat/lon points typically
> stored with the image, or just metadata that allows
> you to navigate the image? <-snap->
About netCDF files I don't know exactly, but I suppose that doesn't make
much of a difference. I do know that for example ENVI's generic file
storage format is some kind of raw data format for the image file,
without any metadata (just the pixel values in one of the 3 supported
interlaced orders), with a second header file to store the metadata. The
image file has no extension by default, the header file has the same
name as the image file plus '.hdr'. In it, amongst others the projection
data are stored, in a lat/lon projection case this would mean for
example the name and datum of the projection (for example lat/lon
wgs84), the coordinates of the cornerspoints of the image (in degrees)
and eventually the pixelsize (also in degrees). That should be enough to
navigate your image, overlay them with each other or vector data, etc.
a typical example for an envi header file has been pasted hereunder.
Note that there is some overlapping information, as envi uses several
items in its header file to store this kind of information, one for the
projection data (map info), one for the corner coordinates and one for
the pixel size. You don't have to use all of them to be able to navigate
and overlay your images, though.
pasted part:
map info = {Geographic Lat/Lon, 1.0000, 1.0000, 92.0000, 29.0000,
0.00892857, 0.00892857, WGS-84, units=Degrees}
geo points = {
1.00000, 1.00000, 29.00000, 92.00000, 8737.00000, 1.00000,
29.00000, 170.00000, 1.00000, 4593.00000, -12.00000, 92.00000,
8737.00000, 4593.00000, -12.00000, 170.00000}
pixel size = {0.008929, 0.008929, units=Degrees}
Cheers,
Vincent.
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