rc - define, store, and read relative coordinate systems
gt 50;rc fs: Make a relative coordinate system with the same center
coordinates and offset type as stack 50.
rc "B335" sl: Name the current relative coordinate system B335 and
store it in your private file of rc systems.
rc nd: Store the name of the current rc system in the default
file of the foreground directory as the default system
for that directory (read automaticly when the stacks
directory is named).
rc u:[pa:33] Change the current rc system to a user defined system
whose y axis has a position angle of 33 degrees in the
coordinate system in which the center coordinates are
rc u:[eqp:1,-3] Change the current rc system to a user defined system
whose equator (x axis) passes through the point
(1,-3) in the current rc system.
In comb a relative coordinate system is needed to make maps and
retrieve by position. Usually it is a coordinate system centered on
the object of interest and parallel to polar or galactic coordinates,
however a user defined coordinate system may have any angle. A
relative coordinate system might also be Ra-dec or l-b.
The name is used for storing or retrieving a relative coordinate system
in a file or printing its defining values.
The fs: option (from stack 1) is usually the easiest way to make a
relative coordinate system. It makes an rc system with the same center
coordinates and offset type as stack 1.
One may also specify the center coordinates in rd: Ra(Hr)-Dec(deg) or
lb: l(deg)-b(deg), and the offset type independently as:
r: polar - dra(hr)-ddec(deg);
g: galactic - dl(deg)-db(deg);
o: observing polar offsets - dra(')-ddec(');
as: observing polar offsets in arcseconds dra(")-ddec(") or dl(")-db("),
depending on the center coordinate type; or
u: user defined offsets - dx-dy with units of ' or deg.
The rotation of a user defined system may be specified either by giving the
position angle for its y axis in the coordinate system of the center coordinates
or by specifying a point in the current system to lie on the equator (x axis).
In the latter case the position angle will be calculated for you.
If a test point is defined in one system, its coordinates will be printed
out in each subsequently defined system to help you understand what is
The macro "prec" in .GMACROS (dm g:) calculates precessed RA-DEC coordinates
from given coordinates and epochs.
This document was last updated on
Tue Oct 17 16:24:05 EDT 2000
by Marc W. Pound.