| Satellite remapping with map_patch [message #49107] |
Sat, 24 June 2006 22:03 |
Leon.Majewski
Messages: 2
Registered: June 2006
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Junior Member |
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Hi
I've got a lot of satellite data (3000 MODIS passes) that I want to
remap to a standard lat/lon grid. It's easy enough to do this with
map_patch after setting the appropriate map projection with map_set:
map_set, 0, mean(area[[1,3]]), 0, /noerase,/noborder,/cylindrical,
limit=area
mapped = map_patch(product,lons, lats, xsize=xsz, ysize=ysz,
xstart=xst, ystart=yst, missing=-999)
The disadvantages are a) generation of interpolated values b) I need to
remap multiple (~15) products for each overpass (ie same transformation
is calulated muliple times).
I'd like to generate an array of indices that are remapped and then use
these to subscript the original data (basically generate the transform
once, apply many times):
index = lonarr(xdim, ydim) ; same size as the input array
transindex = map_patch(index,lons, lats, xsize=xsz, ysize=ysz,
xstart=xst, ystart=yst, missing=-999)
mapped0 = product0[transindex]
mapped1 = product1[transindex]
This doesn't work.
Often there are points in the transindex that missing (-999) - ie the
idl subsrcipt is invalid, but this doesn't matter. A simplified example
that does work (the way I think the above should, including ~missing
points) is:
data = congrid(dist(256), dims[0], dims[1])
index=lindgen(dims[0], dims[1])
index2 = long(rot(congrid(index, xsize, ysize),20)) ;shink and spin to
fake a transform
bp = where(index2 gt 300000L AND index2 lt 400000L)
index2[bp] = -999 ;add some ~missing values
tv, data[index2] ;rescaled, spun array
So, what's the difference between transindex (map_patch) and
rot/congrid of the index arrays? Have I missed something?
Cheers,
Leon
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