Amateur IDL-ENVI problem with Band Math - NV5 Geospatial

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Last Post 30 Jul 2012 12:13 PM by anon

Amateur IDL-ENVI problem with Band Math

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anon

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30 Jul 2012 12:13 PM
Hi, I am amateur in IDL and ENVI I have a problem. I am working with 2 arrays of 1440 x 720 and I made a little function in IDL to run in ENVI and despite that I could compiled it without any problem in IDL and ENVI, when I tried to run in Band math, IDL console tell me that “Expression must be a scalar or 1 element array in this context: .” It is the function: FUNCTION dir_viento, b1, b2, dbl=dbl Wx = b1 Wy = b2 Grad = DOUBLE (180) /!DPI Rad = !DPI /DOUBLE (180) CASE 1 OF (Wx EQ 0) AND (Wy EQ 0): dir = 'ND' (Wx EQ 0) AND (Wy GT 0): dir = DOUBLE (360) (Wx GT 0) AND (Wy GT 0) And (Wx NE Wy): dir = DOUBLE (90) - Grad * (ATAN(Wy /Wx)) (Wx GT 0) And (Wy GT 0) And (Wx EQ Wy): dir = DOUBLE (45) (Wx GT 0) And (Wy EQ 0): dir = DOUBLE (90) (Wx GT 0) And (Wy LT 0) And (ABS (Wx) EQ ABS (Wy)): dir = DOUBLE (135) (Wx GT 0) And (Wy LT 0) And (ABS (Wx) NE ABS (Wy)): dir = DOUBLE (90) + ABS(Grad * (ATAN(Wy /Wx))) (Wx EQ 0) And (Wy LT 0): dir = DOUBLE (180) (Wx LT 0) And (Wy LT 0) And (ABS(Wx) EQ ABS (wy)): dir = DOUBLE (225) (Wx LT 0) And (Wy LT 0) And (ABS(Wx) NE ABS (wy)): dir = DOUBLE (180) + ABS((Grad * (Atan (wx/ABS(wy))))) (Wx LT 0) And (Wy EQ 0): dir = DOUBLE (270) (Wx LT 0) And (Wy GT 0) And (ABS(Wx) NE ABS (wy)): dir = DOUBLE (360) - ABS((Grad * (Atan (wx/ABS(wy))))) (Wx LT 0) And (Wy GT 0) And (ABS(Wx) EQ ABS (wy)): BEGIN dir = DOUBLE (315) END ENDCASE RETURN, Dir END Please, please someone can help me?

Deleted User

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30 Jul 2012 04:32 PM
If Wx and Wy each contain more that the one value you'd like to test, you may have to write a for loop to go through the values individually. The variables above seem to contain multiple value arrays which can't be compared to scalars. Best, Crystal Exelis VIS

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30 Jul 2012 06:11 PM
Crystal I knowledge your help and apologize because I do not speak English very well. I am working with data wind of the Earth surface. Every vector wind is compost for two components (X and Y). I have two arrays (1440 x 720 subarrays) that contain every one component (array Wx and array Wy) of the 1036800 vectors that represent wind in different point of Earth surface in a moment. I understand that IDL works with arrays, and for this reason I do not think I might write a loop, because I run function every “moment of wind record”, every one with 2 arrays. Tanks very much Crystal Jorge Tanks very much Crystal Jorge

MariM

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31 Jul 2012 07:57 AM
It looks like you are trying to create a new array where there are new values assigned based on your two wind vector arrays. You can assign new values to a new array, but you will need to use the WHERE function to find the indices of the pixel values to be replace. This help article does something similar with a classification image - you can see you will need to first generate a new array and then find the array indicies for each newly assigned value and then assign those values. http://www.exelisvis.com/.../ArticleId/4182.aspx

Deleted User

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31 Jul 2012 10:20 AM
Yes I think it could work. Tanks a lot I am going to try to do it and after I send you my result. Jorge

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