POINTING NOTES

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Initialisation

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When a new study is added to the timeline, the sc pointing for each raster
is retrieved from the relevant re-point file;

    /cp/cmdpln/yyyymmdd/re-point_yyyymmddpppp.txt

This 

The new entry is cast as an "eis_structure_container" object. The initial
sc pointing is derived using the method;

    eis_structure_container::initialise_raster_pointing

which calls the routine;

    /planning/timeline/eis_get_study_pointing.pro

for each raster. This function takes as inputs the raster start and stop
times (in TAI). The EIS FOV pointing offsets, as defined in;

    /planning/utilities/eis_pointing_offset.pro

are subtracted from the sc pointing at this stage. The sc pointing is then
returned as a structure of the type

    pointing = {x_point:x_point , y_point:y_point}

back into 

    eis_structure_container::initialise_raster_pointing

For each study-raster (sra), the follwing tags are set;

    sra.x_point = pointing.x_point       Raster X
    sra.y_point = pointing.y_point       Raster Y
    sra.sc_x    = pointing.x_point       SC     X
    sra.sc_y    = pointing.y_point       SC     Y

That is, during initialisation, the raster pointing is set to the sc
pointing. The values of MIP and YIP (yStart) are derived using the function;

    /planning/utilities/eis_get_mirror_position.pro

whose inputs are;

   delx  = difference between sc and raster pointing (sc_x - x_point)
   dely  = difference between sc and raster pointing (sc_y - y_point)
   ra_id = id of raster

In this case (initialisation) delx = dely = 0, so the call is;

    mirror_pos  = eis_get_mirror_position(0. , 0. , ra_id)

which returns a structure of the form;

    mirror_pos = {yStart:yStart , mip:mip}

These are stored

    sra.mip = mirror_pos.mip
    sra.yip = mirror_pos.yStart

Finally, the sra is updated, and the new entry is added to the timeline
container (tlc).

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