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ccdshape - shape of a 2D or 3D distribution based on moments of inertia
Based on intensity weighted
moments of inertia, the center, primary axes and their angles (position
angle, inclination, or euler) are computed.
By default, the three axes in
a cube are treated in the same way, but for astronomical spectral line
cubes the first two (RA-DEC) are different from the third (VEL). In this
case the third axis is decoupled, and instead of sizes and euler angles,
the largest velocity gradient dV/dR and a position angle between kinematic
and morphological major axis is used.
The following parameters
are recognized in any order if the keyword is also given:
Derived sizes are not corrected for any beam shapes and sizes that
may be present in the header of an image.
Taking a disk with a linearly
rising rotation curve at a PA of 30 degrees, and inclination of 60:
- Input image
- Use only values above clip, and below -clip, if only
one value given. If two values given, exclude this range of values. Setting
clip=0 should be sufficient to discard all pixels with the value 0.0. Default:
all values used.
- Use axis world coordinate system descriptors or
the 0-based coordinate axis numbers. Default: true.
- Treat the
3rd axis like a separate velocity axis. This decouples the geometry from
the velocity axis. Default: false.
- Use intensity weighted moments?
The alternative is all pixels equal weight. Default: true.
cross correlations be taken into account? Normally want this, since that
is what gives the position angles, but some codes (e.g. miriad::clstats)
do not do this, so for comparison this option is available. [Default: true]
% mkdisk - 1000 harmonic mass=1 | snaprotate - - 60,30 yz | snapgrid - - nz=64
zrange=-2:2 | ccdshape - clip=0
Size: 64 64 64
Center: -6.25e-05 0.0113125 -0.009375 [wcs]
e_x: 1.00000 0.38733 -0.64866 0.65514 49.1 -59.2
e_y: 1.00000 0.86218 0.50653 -0.00821 90.5 30.4
e_z: 1.00000 -0.32652 0.56803 0.75546 40.9 119.9
qpole: 0.43241 -0.38733 0.64866 -0.65514
0.06310 0.86218 0.50653 -0.00821
0.00034 -0.32652 0.56803 0.75546
16-May-2013 V0.1 Created PJT
19-May-2013 V0.3 added weight= and radecvel= PJT
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