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ccdshape - shape of a 2D or 3D distribution based on moments of inertia


ccdshape [parameter=value]


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:
Input image file [???]
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.
Should 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]


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:
% mkdisk - 1000 harmonic mass=1 | snaprotate - - 60,30 yz | snapgrid - - nz=64
zrange=-2:2 | ccdshape - clip=0
Npoints: 514
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

See Also

snapkinem(1NEMO) , snaprect(1NEMO) , snapinert(1NEMO)




Peter Teuben

Update History

16-May-2013    V0.1 Created    PJT
19-May-2013    V0.3 added weight= and radecvel=    PJT

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