The BPL group

The abbreviation ``BPL'' stands for backprojection lists. Essentially this is the Aperture Response Function describing the visible sky elements from a given detector pixel.

The group JMXi-BPL.-GRP contains a compressed table together with three auxiliary arrays plus vignetting arrays. Table 34 describes those Data Structures.

Table 34: Content of JMXi-BPL.-GRP Group.

Group Member	Description
JMXi-DALL-BPL	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)
JMXi-DAWL-BPL	Number of sky pixels visible from a given detector pixel
JMXi-DAWP-BPL	Array giving the address of the first sky pixel visible from a given detector pixel
JMXi-DAST-BPL	The d_allow_st array contains for each detector pixel the address of the start of the corresponding list in the d_allow array.
JMXi-DMAP-BPL	51 arrays giving the number of detector pixels illuminated from each sky pixel (vignetting arrays). The 51 arrays corresponds to 51 different radius limits covering the range from 75 to 125 mm) used in selecting events from the shadowgrams.

For full description of these and other data structures see the ISDC webpage.