Subject: What should be in the EXPOSURE map ?


Hello Stephane

Jerome has raised the question "What is in the EXPOSURE map?"
He noticed that the unit for this map is 'seconds', but that
the peak value in the map does not correspond to the 
'EXPOSURE' seconds. I now checked the code a found that in
fact I write for each pixel the number of square mm illuminated 
from this sky position multiplied by some normalization factor.
(The code is badly written at this point, first the map is
defined as the product of the exposure time and the illuminated
area (which I think is what is ultimately needed), and then
the map is redefined a few lines later as just the illuminated
area!)

I now wonder if this current way to express the map is something
you, Stephane, have requested to conform with other input to 
'Mosaic_Spec'?
If this is the case we should not change the content but only
the units to 'mm2'. Does Mosaic_Spec take the exposure time from
the header information and multiply each pixel with this value?

JEROME NOTE: In the new version of j_ima_iros now under development 
the exposure map will include the effects of electronic efficiency.
This will mean that the exposure map may vary (will vary!) from 
one scw to the next and you must use the current exposure map in 
your mosaic program like Stephane is doing, and not use the fixed 
maps as you have been doing up to now!

niels