Preload rasters in the background

[lrntct]

Original report by Laurent Courty (Bitbucket: lrntct, GitHub: lrntct).

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When entry data varies a lot, the time needed to load the new raster from the disk could be quite high.
A solution could be to preload the next raster in the background so it could be delivered quickly to the computation module when needed.

[lrntct]

Original comment by Laurent Courty (Bitbucket: lrntct, GitHub: lrntct).

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Next raster could be obtained by returning the map with the minimum start_time that is above the sim_time.
Something like this:

next_maps = [m for m in self.maps[mkey] if m.start_time > sim_time]
min_start_time = min([m.start_time for m  in next_maps])
for m in next_maps:
    if m.start_time == min_start_time:
        next_arr = self.read_raster_map(m.id)