Pick3 and transpose           a6
--------------------------------

   F1 =. > 0 0 5 ; 8 0 2 ; 9 9 3 ; 1 4 1        NB. The photo coordinates.

   3 {. F1                      NB. first three rows of F1
0 0 5
8 0 2
9 9 3

   pic3 =. 3 & {.               NB. A function to get first 3 items
   pic3 F1
0 0 5
8 0 2
9 9 3
   mat =. |:  @  pic3           NB. Transpose after first three
   mat F1                    
0 8 9
0 0 9
5 2 3


