ADD (Ver 5) Polar Coordinate Algorithm

[calvin.harman@…]

Section 1.2.1.13 briefly mentions computation of polar coordinates. I assume
that polar coordinates are to be a lookup from
​ftp://maia.usno.navy.mil/ser7/ser7.dat. Is this correct?

As in the case for UT1-UTC, the lookup table table gives an algorithm for
calculation polar coordinates. Can this be used instead?

According the the SDRS, the return of psTimeGetPoleCoords() is a psSphere. The
members of this struct are RA and dec. Is the data in this table in the same
coodinate reference frame?

If possible, I'd like to move the calculation of Polar Coordinates (ADD section
1.2.1.13) into section 1.2.3 (coordinates) or 1.2.4(projections), given that
these sections deal with coordinate transformations. Is this possible? If so
maybe the function name should change to just psGetPoleCoords()? (Moving this
function would also help reduce circular depencencies with other source files
that use the psTime and psSphere structs).

[Paul Price]

The formula included in the Bulletin A is not accurate for the period covered by
the bulletin, but is a prediction valid beyond the data. Hence there is no
accurate shortcut for interpolating on the table.

The units of the polar coordinates (x,y) in the Bulletin A are arcseconds, so a
psSphere is appropriate.

Including the function in a logical grouping other than psTime is fine. I
included it with the time functions because of its similarity with the ut1-utc
calculation, but I don't think we care exactly in which .h file it resides.

[Paul Price]

Should be fixed in SDRS-07 and ADD-06 (7 September 2004).