| Re: Retrieve pixel values from GeoTIFF [message #73784] |
Sat, 27 November 2010 13:03 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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David Fanning writes:
>
> David Fanning writes:
>
>>
>> mankoff writes:
>>
>>> David: I've also tried using your GeoCoord object, and can display the
>>> graphic and coastlines just fine, but again, am stuck at the step of
>>> "convert (lon,lat)=(-100,-75) to (x,y) for indexing into the original
>>> TIF".
>>
>> mapCoord = GeoCoord('mygeotiff_file.tif')
>> mapStruct = mapCoord -> GetMapStructure()
>> xy = Map_Proj_Forward(lon,lat, Map_Structure=mapStruct)
>> x = xy[0]
>> y = xy[1]
>
> Oh, wait! You said you want to index into the original
> image. (My son is bugging me about bying a car today,
> so I'm distracted. :-)
>
> In addition to the above, I would do this.
>
> mapCoord -> GetProperty, XRANGE=xr, YRANGE=xy
> s = Size(image, /Dimensions)
> xvec = Scale_Vector(Findgen(s[0]), xr[0, xr[1])
> xindex = Value_Locate(xvec, x)
> yvec = Scale_Vector(Findgen(s[1]), yr[0], yr[1])
> yindex = Value_Locate(yvec, y)
>
> Then,
>
> Print, image[xindex, yindex]
Geez! Be sure to type that code with one eye closed!
I have to go look at cars. If you can't figure it out,
I do it right when I return. :-)
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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| Re: Retrieve pixel values from GeoTIFF [message #73785 is a reply to message #73784] |
Sat, 27 November 2010 12:59  |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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David Fanning writes:
>
> mankoff writes:
>
>> David: I've also tried using your GeoCoord object, and can display the
>> graphic and coastlines just fine, but again, am stuck at the step of
>> "convert (lon,lat)=(-100,-75) to (x,y) for indexing into the original
>> TIF".
>
> mapCoord = GeoCoord('mygeotiff_file.tif')
> mapStruct = mapCoord -> GetMapStructure()
> xy = Map_Proj_Forward(lon,lat, Map_Structure=mapStruct)
> x = xy[0]
> y = xy[1]
Oh, wait! You said you want to index into the original
image. (My son is bugging me about bying a car today,
so I'm distracted. :-)
In addition to the above, I would do this.
mapCoord -> GetProperty, XRANGE=xr, YRANGE=xy
s = Size(image, /Dimensions)
xvec = Scale_Vector(Findgen(s[0]), xr[0, xr[1])
xindex = Value_Locate(xvec, x)
yvec = Scale_Vector(Findgen(s[1]), yr[0], yr[1])
yindex = Value_Locate(yvec, y)
Then,
Print, image[xindex, yindex]
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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| Re: Retrieve pixel values from GeoTIFF [message #73786 is a reply to message #73785] |
Sat, 27 November 2010 12:52 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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mankoff writes:
> David: I've also tried using your GeoCoord object, and can display the
> graphic and coastlines just fine, but again, am stuck at the step of
> "convert (lon,lat)=(-100,-75) to (x,y) for indexing into the original
> TIF".
mapCoord = GeoCoord('mygeotiff_file.tif')
mapStruct = mapCoord -> GetMapStructure()
xy = Map_Proj_Forward(lon,lat, Map_Structure=mapStruct)
x = xy[0]
y = xy[1]
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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| Re: Retrieve pixel values from GeoTIFF [message #73787 is a reply to message #73786] |
Sat, 27 November 2010 12:45 |
mankoff
Messages: 131
Registered: March 2004
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Senior Member |
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On Nov 27, 12:06 pm, Paulo Penteado <pp.pente...@gmail.com> wrote:
> On Nov 27, 4:53 pm, mankoff <mank...@gmail.com> wrote:
>
>> I'm trying to get the pixel values (color) from a GeoTIFF file when I
>> have lat,lon arrays. I have the projection set up using MAP_PROJ_INIT,
>> and using MAP_PROJ_FORWARD I can convert from my latitude and
>> longitude to map coordinates, but the map coordinates appear to be in
>> units meter from some reference location. What is the best routine to
>> convert from lat,lon (or u,v) to x,y indices?
>
> It seems that map_proj_forward() can do what you want, you are just
> not giving it the right projection parameters. What is in the geotiff
> structure?
Working through a simpler well-documented example (thanks to David)
here:
http://www.dfanning.com/map_tips/iceshelf.html
The "xy" returned from MAP_PROJ_FORWARD contains negative values, so
this cannot be indices into the image. Should I be using CONVERT_COORD
to go from DATA to DEVICE with the xy array?
David: I've also tried using your GeoCoord object, and can display the
graphic and coastlines just fine, but again, am stuck at the step of
"convert (lon,lat)=(-100,-75) to (x,y) for indexing into the original
TIF".
-k.
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| Re: Retrieve pixel values from GeoTIFF [message #73789 is a reply to message #73787] |
Sat, 27 November 2010 12:13 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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mankoff writes:
> I'm trying to get the pixel values (color) from a GeoTIFF file when I
> have lat,lon arrays. I have the projection set up using MAP_PROJ_INIT,
> and using MAP_PROJ_FORWARD I can convert from my latitude and
> longitude to map coordinates, but the map coordinates appear to be in
> units meter from some reference location. What is the best routine to
> convert from lat,lon (or u,v) to x,y indices?
I use GeoCoord from the Catalyst Library. It reads the
GeoTIFF file, and sets everything up for you automatically. :-)
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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| Re: Retrieve pixel values from GeoTIFF [message #73790 is a reply to message #73789] |
Sat, 27 November 2010 12:06 |
penteado
Messages: 866
Registered: February 2018
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Senior Member
Administrator |
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On Nov 27, 4:53 pm, mankoff <mank...@gmail.com> wrote:
> I'm trying to get the pixel values (color) from a GeoTIFF file when I
> have lat,lon arrays. I have the projection set up using MAP_PROJ_INIT,
> and using MAP_PROJ_FORWARD I can convert from my latitude and
> longitude to map coordinates, but the map coordinates appear to be in
> units meter from some reference location. What is the best routine to
> convert from lat,lon (or u,v) to x,y indices?
It seems that map_proj_forward() can do what you want, you are just
not giving it the right projection parameters. What is in the geotiff
structure?
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