| Re: map_image and latmin/latmax, lonmin/lonmax - edges or centres? [message #86044 is a reply to message #86042] |
Thu, 26 September 2013 05:50   |
Andy Sayer
Messages: 127
Registered: February 2009
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Senior Member |
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I keep meaning to rewrite my mapping routines to include GSHHS but didn't get round to it yet... :)
I think in this case it isn't the IDL borders & boundaries database which is in the wrong, but rather my use of map_image. The reason is that if I draw the data in my image pixel-by-pixel using polyfill it lines up exactly correctly, and it's only when I use map_image that the data is offset from where it should be. So something must be up with these offsets.
Andy
On Wednesday, September 25, 2013 4:35:01 PM UTC-4, David Fanning wrote:
> AMS writes:
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>> After fiddling some more, I agree that it's probably the outer coordinates of the image rectangle that it wants. However, I'm still encountering some odd behaviour. For example, if I take regular 1 degree gridded data and try to map that, things like the US-Canada border (at 49 degrees N) don't lie exactly on grid cell borders (as they should) but are slightly shifted. I'm going to leave it for the rest of the day in case my overtired mind is overlooking something, but
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> if I can't figure it out tomorrow, will create some code which reproduces the issue and post it.
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> You might find that the GSHHS database is more accurate than the
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> database that comes with IDL:
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> http://www.idlcoyote.com/map_tips/gshhs.html
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> Cheers,
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> David
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> --
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> David Fanning, Ph.D.
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> Fanning Software Consulting, Inc.
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> Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
>
> Sepore ma de ni thue. ("Perhaps thou speakest truth.")
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