Geometry Comparison

When converting or preparing geometry, it is useful to compare to other geometry to validate work. Examples of use include:

validating changes to existing pyg4ometry scripts
validating geometry created in pyg4ometry versus another source
comparing different representations
validating conversion between formats

pyg4ometry provides a set of tests for comparing two geometry “trees” that are loaded into memory. Each hierarchy of geometry is navigated and a variety of user-selectable tests are carried out. A result class with details of tests carried out and their outcome is produced and can be easily printed or inpsected programmatically.

When we compare 2 things, we use the terminology reference and other for each. When we need to identify a pair, we use the reference object name. Reference is the object that is the control, or assumed to be the ‘right’ one.

Tests

Which tests to conduct are defined by an instance of pyg4ometry.compare.Tests, which has a set of Boolean options for each test.

The available tests are described below.

Test Name	Description
names	Test whether objects have the exact same name.
namesIgnorePointers	Test whether objects have the exact same name, but whilst ignorign pointer suffixes such as 0x1234567. Note, the geometry will load ok, the name stripping is only for comparison.
nDaughters	Test for a matching number of daughter volumes in a LogicalVolume or AssemblyVolume.
solidExact	Compare the class type of every solid.
shapeExtent	Numerically compare the size of the bounding box (i.e. extent) of each solid.
shapeVolume	Compare the volume as per the visualisation mesh of each shape.
shapeArea	Compare the surface area as per the visualisation mesh of each shape.
placement	Numerically compare the rotation and translations in each placement.
scale	Compare the ‘scale’ for a physical volume that can be used for a relfection. No scale is equal to unit scale [1,1,1].
copyNumber	Compare the copy number for a physical volume.
materials	Whether to do a series of tests of materials in a LogicalVolume.
materialClassType	If doing materials tests, compare the class name of each material.
materialCompositionType	If doing materials tests, compare the class name of each component of a material.
testDaughtersByName	Whether to check daughter volumes by name or by index. If true, then a set of overlapping names is used and the matching ones that exist in both are compared. If false, the daughters are strictly compared in numerical order.

Note

Volumes and areas are based on the polygonal meshes generated for visualisation purposes. These may not be the exact area of a perfect shape, such as a sphere, but an approximation. They will however, be consistently generated. Consider the tolerances also.

Tolerances

When making numerical comparisons (e.g. position of a volume), we must consider the finite numerical precision in a computer. Also, this may be useful as geometry from another source may be practically equivalent, but not exactly at the last decimal place.

Therefore, we include a set of tolerances for numerical comparisons that are included in the Tests class. These are typically fractional.

Note

The fraction is calculated with respect to the reference value. So \(( value_{other} - value_{reference} ) / value_{reference}\).

Variable Name	Default Value	Description
toleranceSolidParameterFraction	1e-3	Maximum fractional difference for any solid parameter.
toleranceSolidExtentFraction	1e-6	Maximum fractional difference for the calculated extent of any solid.
toleranceVolumeFraction	1e-2	Maximum fractional difference in volume.
toleranceAreaFraction	1e-2	Maximum fractional difference in area.
toleranceTranslationFraction	1e-6	Maximum fractional difference for translations in placements.
toleranceScaleFraction	1e-3	Maximum fractional difference in scale parameters in placements.
toleranceRotationFraction	1e-6	Maximum fractional difference in rotation angles in placements.
toleranceMaterialDensityFraction	1e-4	Maximum fractional difference in the density of a material.
toleranceMaterialMassFraction	1e-4	Maximum fractional difference in the mass fraction of a material component.

Running a Comparison

GDML Files

>>> comparison = pyg4ometry.compare.gdmlFiles("file_reference.gdml", "file_other.gdml")
>>> comparison.print()

Logical Volumes

Compare two logical volumes, such as the top volume of a registry from a loaded file.

>>> comparison = pyg4ometry.compare.geometry(refLV, otherLV)
>>> comparison.print()

There are functions to compare individual objects too. These follow the same pattern. A few are:

pyg4ometry.compare.physicalVolumes
pyg4ometry.compare.assemblyVolumes
pyg4ometry.compare.replicaVolumes
pyg4ometry.compare.divisionVolumes - not implemented yet
pyg4ometry.compare.parameterisedVolumes - not implemented yet
pyg4ometry.compare.materials
pyg4ometry.compare.solids

Example Output

For a test that failed the following is an example of output.

Overall result>  TestResult.Failed
Test>  position
(av): a_assembly: (pv): a_a_pv1: a_a_pv1_pos: TestResult.Failed: z: (reference): 100.0, (other): -100.0

Test>  shapeExtentBoundingBoxMin
a_assembly_a_a_pv1: TestResult.Failed: axis-aligned bounding box lower edge: dimension: z, (reference): 85.0, (other): -115.0

Test>  shapeExtentBoundingBoxMax
a_assembly_a_a_pv1: TestResult.Failed: axis-aligned bounding box upper edge: dimension: z, (reference): 115.0, (other): -85.0

Seeing the Results

The return of a comparison is a pyg4ometry.compare.ComparisonResult instance. The most useful function here is the print function, which will print all results but also you can print select sets of tests or only certain results.

See Convert and ComparisonResult for details.

Examples

See pyg4ometry/pyg4ometry/test/pythonGeant4/T7*.py for examples that form the tests of this code.

Only Volume

Here, two ways are shown for creating the set of tests.

>>> import pyg4ometry
>>> t = pyg4ometry.compare.Tests()
>>> pyg4ometry.compare.Tests.printAllTestNames()
    "names"
    "namesIgnorePointer"
    "nDaughters"
    "solidExact"
    "solidExtent"
    "shapeExtent"
    "shapeVolume"
    "shapeArea"
    "placement"
    "scale"
    "copyNumber"
    "materials"
    "materialClassType"
    "materialCompositionType"
    "testDaughtersByName"
>>> t.setAllFalse()
>>> t.shapeVolume = True
>>> comparison = pyg4ometry.compare.gdmlFiles("file1.gdml", "file2.gdml", t)
>>> comparison.print()

or

>>> import pyg4ometry
>>> t2 = pyg4ometry.compare.Tests("shapeVolume")
>>> comparison = pyg4ometry.compare.gdmlFiles("file1.gdml", "file2.gdml", t2)
>>> comparison.print()

Removing a Test

A test can be turned off by name:

>>> import pyg4ometry
>>> t = pyg4ometry.compare.Tests()
>>> t.setFalse("names")