| Re: image interplate and overlay lat/lon? [message #81175] |
Wed, 22 August 2012 10:13  |
beardown911
Messages: 21
Registered: March 2007
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Junior Member |
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On Wednesday, August 22, 2012 10:57:48 AM UTC-5, go cats wrote:
> Hello all,
>
>
>
> My goal is to take an image(s) and overlay geographic lat/lon information onto the image. I have lat/lon information of four boundaries and tried to create a regular grid using them.
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>
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> I’ve used David’s code to generate a regular lat/lon grid, and tried to interpolate image with gridded lat/lon data.
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> However, outImage looks blank and only geographin lat/lon data are shown with 0 image pixel values. I am working on 8-bit tif images.
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> Would anybody give me some tips how to make this work or what I did wrong?
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> Thanks in advance,
>
> Kim
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> P.S. Below is what I've been working on.
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> ;---------------------------------------------------------
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> ; image(0,0)locates at the upper left corner
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> xOrigin = maxLon
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> yOrigin = maxLat
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> xscale = (maxLon – minLon)/nS
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> yscale = (maxLat – minLat)/nL
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> uvec = Findgen(nS) * xscale + xOrigin
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> vvec = yOrigin - (Findgen(nL) * yscale)
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> uarray = Rebin(uvec, nS, nL)
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> varray = Rebin(Reform(vvec, 1, nL), nS, nL)
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> outImage = Interpolate(inImage, varray, uarray)
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> .
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> .
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> .
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> geoTag = { $
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> ModelTiepointTag: [0.0, 0.0, 0.0, xOrigin, yOrigin, 0.0], $
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> ModelPixelScaleTag: [xscale, yscale, 0.0], $
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> GTModelTypeGeoKey: 2, $ ; (ModelType Geographic)
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> GTRasterTypeGeoKey: 2, $ ; (RasterPixelIsPoint)
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> GeographicTypeGeoKey: 4326 $ ; (WGS84)
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> }
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> .
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> .
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> WRITE_TIFF, outImage, GEOTIFF = geoTag
>
> ;-----------------------------------------------------
Thanks David for your prompt answer and guide.
Yes, as you pointed, no interpolate is needed for the input image.
Image array and lat/lon grids have the same size.
I'll read through "Map Structures" and try it.
Thank you again and have a nice day!
Kim
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| Re: image interplate and overlay lat/lon? [message #81176 is a reply to message #81175] |
Wed, 22 August 2012 09:49  |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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go cats writes:
> My goal is to take an image(s) and overlay geographic lat/lon information onto the image. I have lat/lon information of four boundaries and tried to create a regular grid using them.
>
> I?ve used David?s code to generate a regular lat/lon grid, and tried to interpolate image with gridded lat/lon data.
>
> However, outImage looks blank and only geographin lat/lon data are shown with 0 image pixel values. I am working on 8-bit tif images.
>
> Would anybody give me some tips how to make this work or what I did wrong?
After doing a bit of research, I guess this is the right way
to create a GeoTiff grid with an equal-area cylindrical (called
other names!) projection. Although, I really don't know what
"Raster Pixel is Point" means. It seems to me a raster pixel
describes an area.
Anyway, I don't see any reason for Interpolating the input
image. Presumably your grid *describes* the input image.
If you really want to make it another size, I would use
Congrid. That has the advantage of doing the interpolation
correctly and in a way I don't have to worry about it. :-)
As far as not seeing anything, is this because you haven't
scaled the data, or because you tried to interpolate byte
data, or ... God only knows what.
I would *guess* your image might be upside down. When I
work with images and GeoTiff files, I always reverse the
Y direction when I read from the Tiff file, and reverse
it again when I write it.
Write_Tiff, Reverse(outimage,2), GEOTIFF=geoTag
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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| Re: image interplate and overlay lat/lon? [message #81250 is a reply to message #81177] |
Mon, 27 August 2012 03:49 |
Yngvar Larsen
Messages: 134
Registered: January 2010
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Senior Member |
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On Wednesday, 22 August 2012 18:26:11 UTC+2, David Fanning wrote:
> go cats writes:
> Maybe there are GeoTiff files that use latitude and longitude values for
> the tie points and scales, but I've never seen any. All the GeoTiff
> files I've ever worked with use projected meter values and include
> information about the map projection in the file.
<OffTopic>
The near-global digital elevation model data from the NASA Shuttle Radar Topography Mission, see http://srtm.csi.cgiar.org/, is distributed on a latitude/longitude grid, as GeoTIFF. Due to its "near-globalness", obviously.
</OffTopic>
--
Yngvar
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