Advanced tutorials

Finding volumes

Before editing geometry it is useful to find a logical volume. The registry contains all the logical volumes using the GDML in pyg4ometry/pyg4ometry/test/gdmlG4examples/ChargeExchangeMC/

import pyg4ometry
r = pyg4ometry.gdml.Reader("lht.gdml")
reg = r.getRegistry()

The registry instance reg has a member variable called logicalVolumeDict so calling

reg.logicalVolumeDict.keys()

should print

In [4]: reg.logicalVolumeDict.keys()
Out[4]: odict_keys(['vMonitor', 'vMonitorBack', 'vTarget', 'vTargetInnerCover', 'vTargetColumn', 'vTargetInnerColumn',
                    'vTargetVacuumSpace', 'vTargetOuterCover', 'vCrystal', 'vCrystalRow', 'vCalorimeter', 'vVetoCounter',
                    'vOuterFerrumRing', 'vInnerFerrumRing', 'vInnerCuprumRing', 'vTargetWindow', 'vTargetWindowCap',
                    'vTargetWindowMylarCover', 'vTargetWindowAluminiumCover', 'vWorldVisible', 'World'])

then the LogicalVolume can be obtained simply from the dictionary

lv = reg.logicalVolumeDict['vTargetInnerColumn']

This lv can be used for manipulating geometry, passing to visualisers etc.

Navigating the LV-PV hierarchy

There is a hierarchy of LV-PVs to describe a GDML/Geant4 geometry. An LV in terms of geometry consists of an outer solid lv.solid and lv.daughterVolumes. lv.solid is one of the pyg4ometry.geant4.solid types which match the GDML/Geant4 solids. lv.daughterVolumes is a list of pyg4ometry.geant4.PhysicalVolumes.

The best way to explore the methods and data members of pyg4ometry.geant4.LogicalVolume and pyg4ometry.geant4.PhysicalVolume is to explore in iPython. See cute video based on the lht.gdml example above.

Edit existing geometry

After loading some geometry it is possible to modify the memory resident geometry. This could adjusting the parameter of a given solid or PV, or replacing entirely the type of solid used for an LV. To edit geometry a LV instance is required

Complex geometry builder

Having access to geometry construction in python allows the rapid construction of geometry using functions which return an appropriate LV. Examples of this available in pyg4ometry/pyg4ometry/test/pythonCompoundExamples

Fluka geometry scripting

In a very similar way to geant4 geometry authoring it is possible to use pyg4ometry to create fluka output. To create a simple region consisting of a single body

import pyg4ometry.convert as convert
import pyg4ometry.visualisation as vi
from pyg4ometry.fluka import RPP, Region, Zone, FlukaRegistry

freg = FlukaRegistry()

rpp = RPP("RPP_BODY", 0, 10, 0, 10, 0, 10, flukaregistry=freg)
z = Zone()
z.addIntersection(rpp)
region = Region("RPP_REG", material="COPPER")
region.addZone(z)
freg.addRegion(region)

greg = convert.fluka2Geant4(freg)
greg.getWorldVolume().clipSolid()

v = vi.VtkViewer()
v.addAxes(length=20)
v.addLogicalVolume(greg.getWorldVolume())
v.view()

Export scene to paraview/vtk

1import pyg4ometry

Export scene to unity/unreal

The quickest way to get geometry to Unity/Unreal is to use a standard asset format. This takes a vtkRenderer and creates a OBJ file. The vtkRenderer managed within pyg4ometry from the vtkViewer class, once a geometry is created (either from any source) then an OBJ file can be created. Taking the example in pyg4ometry/pyg4ometry/test/pythonCompoundExamples/

import pyg4ometry
r = pyg4ometry.gdml.Reader("./Chamber.gdml")
l = r.getRegistry().getWorldVolume()
v = pyg4ometry.visualisation.VtkViewer()
v.addLogicalVolume(l)
v.exportOBJScene("Chamber")

obj files are written Chamber.obj and Chamber.mtl.

For a Fluka file, first it must be converted to geant4 and then the same process should be followed.

import pyg4ometry
r = pyg4ometry.fluka.Reader("./Chamber.inp")
greg = pyg4ometry.convert.fluka2geant4(r.getRegistry())
l = greg.getWorldVolume()
v = pyg4ometry.visualisation.VtkViewer()
v.addLogicalVolume(l)
v.exportOBJScene("Chamber")

As the meshing might need to changed for the visualisation application, the parameters for the meshing for each solid might need to changed.

An obj file for an entire experiment does not help with work flows where meshes have to be UV-ed and textured. Tools like Blender and Gaffer can be used for this workload but require meshes for each object and their placement. To enable there is a special writer

import pyg4ometry
r = pyg4ometry.gdml.Reader("./Chamber.gdml")
l = r.getRegistry().getWorldVolume()
w = pyg4ometry.visualisation.RenderWriter()
w.addLogicalVolumeRecursive(l)
w.write("./SphericalChamber")

The directory SphericalChamber contains all the meshes in OBJ format along with an instance file 0_instances.dat which contains a row for each instance of a mesh.