I guess this isn't a bug but more of just a request to right a poor decision. The coordinates for GPS don't match actual spherical coordinates. Why is theta=0 pointing the wrong way? "Incident with zenith angle θ=0 means the particle is travelling along the -z axis." This makes no sense! I realize you cannot fix this mistake now that people expect it, but if you could please add a new angular distribution like "isotropic+z" so that theta=0 corresponds to +z direction as it is found for every spherical coordinate system in every textbook in the world. Thanks!
Hi, you are right saying these commands are confusing in many simple occasion, especially for simple use-cases (GPS is designed for complex sources). May I ask you to please share the list of GPS commands you are using? Or alternatively what you want to achieve. I would like to cross-check one thing, Thank you, Andrea
Hi Andrea, Thanks for the reply. I was quite frustrated yesterday when I was using the GPS as things were looking odd. Only to eventually learn that theta is defined as the angle between the particle direction and -z (not +z). Here is an example of throwing protons at theta=30 +-1 degree (in global coordinates). /gps/particle proton /gps/pos/type Volume /gps/pos/shape Cylinder /gps/pos/centre 0 0 0 cm /gps/pos/halfz 10 cm /gps/pos/radius 0.1 mm /gps/ang/type iso /gps/ang/mintheta 149.0 deg /gps/ang/maxtheta 151.0 deg /gps/ang/minphi 0 deg /gps/ang/maxphi 360 deg /gps/ene/type Mono /gps/ene/mono 5.3154 MeV The confusing bit is: /gps/ang/mintheta 149.0 deg /gps/ang/maxtheta 151.0 deg Ideally, it would be: /gps/ang/mintheta 29 deg /gps/ang/maxtheta 31 deg What is not immediately obvious is if this is still a right handed coordinate system. If it is so, should I expect (theta=90,phi=0) to point in the -x direction? From my quick tests, it *is not* a right handed coordinate system: * (theta=90,phi=0) = -x (global) * (theta=90,phi=90) = -y (global) * This means the local x cross y is point in the +z (global) direction. My suggestion (for the sake of compatibility) is to add the following command: /gps/ang/type iso+z where theta and phi are those of the global coordinate system. Cheers, Whit PS We spoke at Jlab a few weeks ago and I asked about an official git repository. Does one exist yet? This is the type of thing I could easily add myself.
Hello, This issue will be transformed into a work item for the 2017 work-plan. Unfortunately due to man-power issues we have not been able to find a faster solution to improve GPS. Considering that this could be considered more a "feature request" and not a "bug" I take the liberty to close the issue. Andrea
