| Re: Land Mask data set available? (in lat and lon) [message #29254 is a reply to message #29171] |
Fri, 08 February 2002 07:01   |
Robert Stockwell
Messages: 74
Registered: October 2001
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Member |
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Mark Hadfield wrote:
> "Robert Stockwell" <stockwell@co-ra.com> wrote in message
> news:3C62F3C6.3090502@co-ra.com...
>
>> ...
>> 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.
>> ...
>> 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).
>> ...
>> Does someone have that in IDL?
>> (or rather, a data format that can be easily digested
>> into IDL)
>>
>
> Thanks for the link to the land-sea mask data. I wasn't aware of that one. I
> agree that it might be awkward inverting their map projection. There's been
> some discussion on the group in the past about accessing IDL's built-in
> projections. A Google search might turn up something useful.
>
> I don't have a land-mask data set, but I do have a routine that calculates a
> land mask (in fact a land fraction) for a specified grid using vector
> shoreline data from the GSHHS data set:
>
> http://www.ngdc.noaa.gov/mgg/shorelines/gshhs.html
>
> Getting this working on your system would be non-trivial, but if you want to
> try I'll be glad to help.
Thanks for the info Mark. I took a look at the webpage, and it looks
promising. Is your routine in entirely in IDL, partly in IDL, or C.
(do you use the C code to read the data that they provide?)
Andrew Cool also suggested using GTOPO30 DEM data, with which he
produced a great looking jpg of a landmask. This seems to perhaps
be in a better form to extract the lat and lon data that I require
than the link I first mentioned (above), since they appear to be
in 30 arc second spacing,rather than in 1km spacing.
http://edcdaac.usgs.gov/gtopo30/gtopo30.html
So that actaully sounds pretty good. I'll still have to figure
out how to read the files, perhaps Andrew can help with that.
Cheers,
bob
> ---
> Mark Hadfield
> m.hadfield@niwa.co.nz http://katipo.niwa.co.nz/~hadfield
> National Institute for Water and Atmospheric Research
>
>
>
>
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