Important shifts in light interception

[Emblanc]

The high PAR values comes from the way sumPAR is computed:

1) On relevant organ, PAR is computed as : Ei (PAR irradiance) * area_of_the_primitive 2) Tiller_surface is computed as the sum of visible_area of all relevant organ belonging to an axis (with math formulae + estimate of visibility) 3) organ PAR are summed per axis and divided by tiller_surface and Temperature ???, to get a 'corrected for visibility (and temperature ??)' irradiance (called sum_PAR)

The strange values for sum_PAR occur when the tiller_surface << sum(primitive_area). For example, >at the considered time step, the tiller_surface of axe (1,2,1) of plant 3 is less than 1 % of the sum of >primitive organ area, whereas for other axes it is from 3 to 50 %.

These discrepancies can come from discretisation effects (math cylinder area are not equal to primitive area) and bugs/ problems in visibility computation (it is difficult to assess a priori what part of the primitive is exposed to light when geometric object are intricated and when light comes from several directions)

Probably the best solution will be to switch to the representation of 'only visible' part of organs (PR #9) and compute tiller area as the sum of contributing primitives

[Emblanc]

Now there is a test to check for important shifts in light interception. And PR #9 solved this issue