difference between punctual receiver and surface receiver

[leofuy]

Hi,
We are having big differences between punctual receiver and surface receiver in t15 and t30.
With surface receiver we have TR15 = 1.53 s (taken by cursor value in the position of the punctual receiver) and TR30 = 3.20
And with punctual receiver we obtain TR15 = Global 6.27 / Average 6.04 and T30 = Global 5.48 / Average 5.15.
What do you think it could be happen?
Thanks for your time.
Leonardo

[nicolas-f]

Hi,

See #372 to understand the difference

[leofuy]

Hi,
How must be resolved?
(#372 (comment))
The code must be rewriten?
thanks
Leonardo

#372 (comment)

Let's start with the source of angle dependency. In general you are right that in SPL mode the angle dependency should be neglected, in receiver's Intensity mode we include the angle dependency.

The source code for energy recording on surface receivers is in reportmanager in lines 187-190 and repeated for different surface receiver type in lines 281-284:

if(*(this->paramReport.configManager->FastGetConfigValue(Core_Configuration::I_PROP_SURFACE_RECEIVER_MODE))==0)
(itrs)->data[particleInfos.frequenceIndex][CellRow][CellCol][particleInfos.pasCourant]+=particleInfos.energiecosf(normal.angle(particleInfos.direction));
else
(*itrs)->data[particleInfos.frequenceIndex][CellRow][CellCol][particleInfos.pasCourant]+=particleInfos.energie;
As I said before in Intensity mode we explicitly multiply the energy with cosine of angle of incidence, but in SPL mode there is no such thing, but... This code is wrong, as when we look at ray propagation and the way it hits the surface we get an image like this (note that dA and spacing between rays is equal in both cases):

When rays are perpendicular to the surface there is higher ray density per differential surface dA than in case of oblique angles. This makes the angle dependency implicit in general ray tracing and ray-surface intersection. As a side note - this is not the case with point receivers as for point we always assume that the ray is perpendicular to the differential surface.

Therefore we now have two sources of angle dependency in surface receiver - explicit: written directly in the code and implicit: due to the nature of ray tracing. Now when we take into account the fact that implicit dependency is always present the right code for the energy recording is as follows:

if (*(this->paramReport.configManager->FastGetConfigValue(Core_Configuration::I_PROP_SURFACE_RECEIVER_MODE)) == 0)
face->recepteurS->energieRecu[particleInfos.frequenceIndex][particleInfos.pasCourant] += particleInfos.energie;
else
face->recepteurS->energieRecu[particleInfos.frequenceIndex][particleInfos.pasCourant] += particleInfos.energie / max(cosf(normal.angle(particleInfos.direction)), 0.000000001f);
In Intensity mode we rely on implicit angle dependency, so there is no multiplication. In SPL mode we compensate the dependency by dividing the energy with the cosine of angle of incidence. The max() is there to avoid division by zero.

Finally, the corrected code gives correct results in the model you provided in SPL mode.