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Re: Land Mask data set available? (in lat and lon) [message #29237 is a reply to message #29173]

Fri, 08 February 2002 11:24

Kelly Dean
Messages: 92
Registered: March 1997

Member

Try the 1km Global Land Cover Characteristics Database from USGS
(usgs2_0g.img.gz). Water bodies (including lakes) have the byte value
of 16, but this should be easy to convert to the desired 1's and 0's.

http://edcdaac.usgs.gov/glcc/globdoc2_0.html

It is easy to compute the navigation --

lin = ( 89.99583333333334 - lat ) / 0.00833333333333
ele = ( -179.99583333333334 - lon ) / 0.00833333333333

GTOPO30 is a good source for land/sea mask, but remember, these are 33
separate tiles. With 6 tiles covering your region of interest. However,
I do recall there is one separate tile covering Antarctic in a different
projection. The Global Land Cover Database is one big binary file.

Kelly Dean
CSU/CIRA

Robert Stockwell wrote:

> Greetings All,
> I was just about to assimilate the land mask info
> into IDL, but for my purposes I need the land mask
> as a function of lat and lon (so as to branch my
> algorithm on whether or not a data point falls on land),
> rather then merely an image.
>
> Thus I want to have something like
> landmask = int(nx,ny)
> lon = float(nx,ny)
> lat = float(nx,ny)
>
> that I can crunch into an array for my lat, lon sampling
> and then directly compare my data with the landmask value.
> (a simple water = 0, land = 1 mask is fine for me)
>
> I am interested in the southern hemisphere
> (frinstance 40S to 80 south), and 1/2 degree by 1/2 degree
> or better.
>
> Does someone have that in IDL?
> (or rather, a data format that can be easily digested
> into IDL)
>
> Cheers,
> bob stockwell
>
> PS
>
> I am about to use the land=sea mask data from:
> http://edcdaac.usgs.gov/1KM/land_sea_mask.html
> that i found snooping through google. It looks like
> I'll have to grab their image which appears to be in
> a km by km sampling, and calculate the inverse transform
> from their map projection into lat and lon (ugh).
>
> Or perhaps I can use the map commands i IDL and
> create an image, grab the image, convert from pixels to
> lat and lon.
>
> I am hoping there is an easier way, or at least a
> "already done" way

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[Message index]

		Land Mask data set available? (in lat and lon) By: Robert Stockwell on Thu, 07 February 2002 13:38
		Re: Land Mask data set available? (in lat and lon) By: Kelly Dean on Fri, 08 February 2002 11:24
		Re: Land Mask data set available? (in lat and lon) By: wmconnolley on Fri, 08 February 2002 01:43
		Re: Land Mask data set available? (in lat and lon) By: Mark Hadfield on Mon, 11 February 2002 11:54
		Re: Land Mask data set available? (in lat and lon) By: Robert Stockwell on Mon, 11 February 2002 05:20
		Re: Land Mask data set available? (in lat and lon) By: Robert Stockwell on Mon, 11 February 2002 05:08
		Re: Land Mask data set available? (in lat and lon) By: Klaus Scipal on Mon, 11 February 2002 00:22

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