| Re: Help on comparing 2 arrays [message #70635] |
Tue, 27 April 2010 02:13 |
d.poreh
Messages: 406
Registered: October 2007
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Senior Member |
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On Apr 26, 7:48 pm, Aram Panasenco <panasencoa...@gmail.com> wrote:
> Dave Poreh wrote:
>> Folks
>> I am trying to compare on ground (on sea!) laser data with MERIS data
>> for chlorophyll. Actually I have 2 arrays L[lat1, long1, c1] for on
>> ground measurements (with 400 meters resolution) and C[lat2, long2,
>> c2] for satellite data. What I want is this: for each pixel of C
>> (satellite data) extract data from array L that dropped inside of this
>> pixel. For instance for some pixels I have 3 or 4 data from L or
>> whatever. Does anyone have some good idea how to do this?
>> Any help highly appreciated.
>> Cheers
>> Dave
>
> Hey Dave,
>
> Are the latitude-longitude arrays in integer or floating-point format?
> Either way, you might want to specify an extraction radius - how close
> to each other do two points have to be to count them as the same point?
> I would define DELTA_LAT and DELTA_LON constants for that at the start
> of the routine.
>
> Note: I see your arrays are in the format [latitude,longitude], so I
> will stick with that, but the normal convention is obviously
> [longitude,latitude]
>
> I would then sort the L array in ascending latitude and ascending
> longitude orders:
>
> sortL_Lat = sort(L[0,*])
> sortL_Lon = sort(L[1,*])
>
> Then run a for-loop for every point in C and determine the indices of L
> where the point falls within the latitude range AND the longitude range.
> That gives you the indices of where to extract your L data for each
> point and do whatever you want with it.
>
> If the radius calculations have to be a little more precise than that,
> you can use the MAP_2POINTS routine on the points obtained using
> delta-longitude and delta-latitude comparison, and throw away the ones
> that are farther than some radian value away. Don't forget that the
> MAP_2POINTS routine accepts data in the longitude,latitude format as
> opposed to your data format! ;)
>
> Good Luck!
>
> ~Aram Panasenco
Thanks Guys
I did apply both way and they are brilliant. Chris’s way is so fast
because there is no for loops. Actually what I have done until now is
extracting the satellite cells that ship went along (because my L
array in L[lat1, long1, c1] format), but sounds like it is better to
do comparison with the original scenes as Chris suggested. I give it a
try with that way also.
Cheers
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| Re: Help on comparing 2 arrays [message #70641 is a reply to message #70635] |
Mon, 26 April 2010 19:48  |
Aram Panasenco
Messages: 41
Registered: April 2010
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Member |
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Dave Poreh wrote:
> Folks
> I am trying to compare on ground (on sea!) laser data with MERIS data
> for chlorophyll. Actually I have 2 arrays L[lat1, long1, c1] for on
> ground measurements (with 400 meters resolution) and C[lat2, long2,
> c2] for satellite data. What I want is this: for each pixel of C
> (satellite data) extract data from array L that dropped inside of this
> pixel. For instance for some pixels I have 3 or 4 data from L or
> whatever. Does anyone have some good idea how to do this?
> Any help highly appreciated.
> Cheers
> Dave
Hey Dave,
Are the latitude-longitude arrays in integer or floating-point format?
Either way, you might want to specify an extraction radius - how close
to each other do two points have to be to count them as the same point?
I would define DELTA_LAT and DELTA_LON constants for that at the start
of the routine.
Note: I see your arrays are in the format [latitude,longitude], so I
will stick with that, but the normal convention is obviously
[longitude,latitude]
I would then sort the L array in ascending latitude and ascending
longitude orders:
sortL_Lat = sort(L[0,*])
sortL_Lon = sort(L[1,*])
Then run a for-loop for every point in C and determine the indices of L
where the point falls within the latitude range AND the longitude range.
That gives you the indices of where to extract your L data for each
point and do whatever you want with it.
If the radius calculations have to be a little more precise than that,
you can use the MAP_2POINTS routine on the points obtained using
delta-longitude and delta-latitude comparison, and throw away the ones
that are farther than some radian value away. Don't forget that the
MAP_2POINTS routine accepts data in the longitude,latitude format as
opposed to your data format! ;)
Good Luck!
~Aram Panasenco
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| Re: Help on comparing 2 arrays [message #70646 is a reply to message #70641] |
Mon, 26 April 2010 07:52 |
rogass
Messages: 200
Registered: April 2008
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Senior Member |
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On 26 Apr., 11:29, Dave Poreh <d.po...@gmail.com> wrote:
> Folks
> I am trying to compare on ground (on sea!) laser data with MERIS data
> for chlorophyll. Actually I have 2 arrays L[lat1, long1, c1] for on
> ground measurements (with 400 meters resolution) and C[lat2, long2,
> c2] for satellite data. What I want is this: for each pixel of C
> (satellite data) extract data from array L that dropped inside of this
> pixel. For instance for some pixels I have 3 or 4 data from L or
> whatever. Does anyone have some good idea how to do this?
> Any help highly appreciated.
> Cheers
> Dave
Hi Dave,
maybe you can do this in the following way (as far as I understood
what you want to do):
1. make a large array with a cell size of 10m covering the maximum
spatial dimensions of the largest array
2. make the array 3D
3. fill in 2D layer 1 your congrid(finite(L1),newsize), in layer2 your
congrid(finite(L2),newsize) and in layer3 your
congrid(finite(C),newsize), whereas in each layer the cells are
covered according the spatial dimensions of the input - so for one
MERIS cell 26x30 cells must contain a 1
4. ask for each 26x30 cell by where(total(array,3) gt 1) for the
related L1 or L2 measurements
5. rewrite the code to avoid for loops :)
I hope it helps somehow
Cheers
CR
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