| Re: an envi question- extracting the pixel values of seveal points with lat-lon values [message #51073 is a reply to message #51007] |
Thu, 02 November 2006 13:18  |
jeffnettles4870
Messages: 111
Registered: October 2006
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Senior Member |
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Well, the general idea is to write a quick routine that does the
following for each image:
1) calls ENVI_CONVERT_PROJECTION_COORDINATES to convert your lat/lon
points to the projection of your image.
2) calls ENVI_CONVERT_FILE_COORDINATES to convert the results from 1)
into file coordinates (the col/row coordinates for the pixels you need)
3) call ENVI_GET_DATA using the coordinates you got from 2) to give you
the brightness values of your image at those coordinates.
This is a general scheme b/c i don't know the projection info for your
images, though it doesn't appear that you even need to know.
ENVI_CONVERT_FILE_COORDINATES seems to be smart enough to figure that
out for you. I wasn't clear from what you said, but I think you
mentioned that you might get a new image every hour or so? If so, you
might want to write some code that checks for a new image and then
calls your routine that does 1-3 above on any new images you get.
I have to say, though, that I'm curious as to why Ed had to write all
that code, b/c it makes me wonder if i've missed something (this is
what usually has happened in cases like these :( ), or whether or not
these are just brand new routines that weren't available when he needed
them. If that's the case, sorry Ed, I feel your pain :(
Jeff
gis_learner wrote:
> Dear All,
>
> Thank you very much. For all. I did not want to cause a
> problem...Anyway I did..
>
> Jeff is righ that the field gathered point data is in lat long...
>
> Jean is also right that the images daily... Sometimes hourly...
>
> Now may I ask what to do? :)
>
> jeffnettles4870@gmail.com wrote:
>> Oh yeah, forgot to include that part :) And I also should've included
>> that, since the original poster's data are in lat/lon values, a call to
>> ENVI_CONVERT_PROJECTION_COORDINATES might also be in order.
>>
>> Jeff
>>
>>
>> Jean H. wrote:
>>> I think 'gis_learner' wanted the value on the different images.... not
>>> only the coordinate of the point. So once the image is opened and the XY
>>> coordinated obtained, I would go for ENVI_GET_DATA ... you can loop
>>> through your points, setting DIMS accordingly.
>>>
>>> Jean
>>>
>>> PS: and the whole code remains small :-)
>>>
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