Gnomonic projection: celestial coordinates in
red -
native coordinates in grey
|
Prev
1
2
3
4
5
6
7
8
9
10
11
Next
-
Native spherical coordinates are not often of primary interest.
-
Need to define a spherical coordinate rotation from native
coordinates to the celestial spherical
coordinates of interest.
-
Final step in the algorithm chain:
-
Spherical rotation specified by three Euler angles.
-
For historic & practical reasons, these Euler angles are defined in
a way which relates them to the image - indirectly via
CRVALi.
-
First-order approximation holds at the reference point (for most
projections, default LONPOLE):
-
Third Euler angle must be specified - need new keyword(s).
-
Additional FITS keywords:
LONPOLE, LATPOLE.
|