| Re: Map image with a sparse array [message #18758 is a reply to message #18662] |
Thu, 27 January 2000 00:00  |
William Daffer
Messages: 34
Registered: February 1999
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Member |
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"Liam E. Gumley" <Liam.Gumley@ssec.wisc.edu> writes:
> whdaffer@my-deja.com wrote:
>
>> Can anyone see what I'm doing wrong?
>>
>> When I tv the mapped image and compare it to the unmapped image, it's
>> clear that the mapped image has included some 'bad' data in the
>> calculations of points within the grid.
>>
>> To be fair, this possibility is not explicitly excluded in the help
>> file. If I'm reading it correctly, all it says is that output grid
>> values which are within the valid mapping limits but which exceed input
>> maxima will be set to the 'bad data' value, not that the input 'bad
>> data' value will be excluded from caluclations.
>>
>> The effect is not large, but it isn't small either. The person I'm
>> doing the work for noticed it right off.
>>
>> By the way, I did try your method first, (bytscl, then map_image) and
>> got similar results, but thought that I should make the bytscl be the
>> last step, since it reduces the 'color' resolution from 360 values to
>> about 200. I'll go back and try your method again. Perhaps there's some
>> magic that I'm not seeing.
>
> William,
>
> I pulled that section of code from a procedure that projects a 720x360
> global grid with missing data onto various map projections. I cannot see any
> hint that the missing data corrupted the resulting image:
> ftp://origin.ssec.wisc.edu/pub/gumley/IDL/grid_project002.gi f
>
> Cheers,
> Liam.
>
Liam;
It looks like your array is considerably more filled-out than
mine.
Go to ftp://catspaw.jpl.nasa.gov/pub/sparse-array
The three files therein are:
h_mss_c249-v1.jpg : map_image then bytscl
h_mss_c249-v2.jpg : bytscl then map_image
tarray.gif : The data, array size unchanged,
bytscl'd and tv'd only
The colored lines in tarray.gif are the data, the grey background
are the grid elements with no data.
I keep meaning to have a close look at map_image, but other
exigencies have intruded. I'm not at all sure that this isn't a
problem of my own making.
William
--
Outside of a dog, a book is man's best friend.
Inside of a dog, it's too dark to read.
Groucho Marx.
Public Key: http://home.earthlink.net/~whdaffer/#PGP-public-key
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