The d_allow array contains for each detector pixel a list of sky
directions which have access to this pixel. ("access" here means
that more half the pixel area is visible from above the mask along
the direction in question)
The number of sky-bins in the list corresponding to a given detector
pixel is given as an entry in the d_allow_l array, the full 16-bit
address of the first direction having access to the pixel is given
in the d_allow_p array.
The list itself is organized as a difference list: each direction
defined by an 8-bit unsigned number giving the difference between
in addresses of the previous direction and the current direction.
Should two directions differ by more than 254 units, the difference
will be written by N bytes with the value 255 and finally a byte
with the remaining difference (after subtraction of N*255) |