3.6. Ellipses #
Within pgSphere, ellipses are defined as :
If the center of any spherical ellipse is the North Pole, the perpendicular projection into the
x-y-plane gives an ellipse as in two-dimensional space.
Use cases are:
cluster or nebula on the sky sphere where the `height' is lower than the `width'
to describe a position error
An ellipse always has:
a major radius
rad_1a minor radius
rad_2a center
centera position angle
pos(inclination)
Hence, the input syntax is:
< { rad_1, rad_2 }, center, pos >Note
The radii
rad_1andrad_2have to be less than 90°.If
rad_1is less thanrad_2, the values will be swapped.The position angle
posis defined within pgSphere as a counterclockwise rotation around the ellipse center and is zero, if the ellipse is “parallel to the equator”
Example 3.9. Input of a spherical ellipse
An ellipse has a center at 20° longitude and 0° latitude. The minor radius is part of the equator. The major radius is 10°, the minor radius is 5°.
sql> SELECT sellipse '< { 10d, 5d } , ( 20d, 0d ), 90d >';