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Detector Definition and Response
geometry/test/cylinder_geometry
--> to define the details of the cylinder geometry, by specifying:
nPhi - number of lines per Phi
nZ
- number of Z points
nRho - number of Rho points
The new settings will be applied to the cylinder_test command.
geometry/test/cylinder_scaleZ
--> to define the resolution of the cylinder geometry, by specifying
the fraction scale for points along Z.
The new settings will be applied to the cylinder_test command.
geometry/test/cylinder_scaleRho
--> to define the resolution of the cylinder geometry, by specifying
the fraction scale for points along Rho.
The new settings will be applied to the cylinder_test command.
geometry/test/recursion_start
--> to set the initial level in the geometry tree for starting the
recursion (default value being zero, i.e. the world volume).
The new settings will then be applied to any recursive test.
geometry/test/recursion_depth
--> to set the depth in the geometry tree for recursion, so that
recursion will stop after having reached the specified depth (the
default being the full depth of the geometry tree).
The new settings will then be applied to any recursive test.
To detect overlapping volumes, the built-in test uses the intersection of solids with linear trajectories. For example,
consider Figure 4.4:
Figure 4.4. Different cases of placed volumes overlapping each other.
Here we have a line intersecting some physical volume (large, black rectangle). Belonging to the volume are four
daughters: A, B, C, and D. Indicated by the dots are the intersections of the line with the mother volume and the
four daughters.
This example has two geometry errors. First, volume A sticks outside its mother volume (this practice, sometimes
used in GEANT3.21, is not allowed in Geant4). This can be noticed because the intersection point (leftmost
magenta dot) lies outside the mother volume, as defined by the space between the two black dots.
The second error is that daughter volumes A and B overlap. This is noticeable because one of the intersections
with A (rightmost magenta dot) is inside the volume B, as defined as the space between the red dots. Alternatively,
one of the intersections with B (leftmost red dot) is inside the volume A, as defined as the space between the
magenta dots.
Each of these two types of errors is represented by a line segment, which has a start point, an end point, and, a
length. Depending on the type of error, the points are most clearly recognized in either the coordinate system of
the volume, the global coordinate system, or the coordinate system of the daughters involved.
Also notice that certain errors will be missed unless a line is supplied in precisely the correct path. Unfortunately,
it is hard to predict which lines are best at uncovering potential geometry errors. Instead, the geometry testing
code uses a grid of lines, in the hope of at least uncovering gross geometry errors. More subtle errors could easily
be missed.
Another difficult issue is roundoff error. For example, daughters C and D lie precisely next to each other. It is
possible, due to roundoff, that one of the intersections points will lie just slightly inside the space of the other. In
addition, a volume that lies tightly up against the outside of its mother may have an intersection point that just
slightly lies outside the mother.
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