Gary, firstly, the full source code isn't found on that website you linked. When searching google, I found the following:
http://www.freevbcode.com/ShowCode.asp?ID=464VSOP87 Functions used to Compute Planetary Positions (1.15 MB)
These functions are a VB version of the complete VSOP87 planetary theory designed to be used to in a program to compute the heliocentric ecliptic longitude, latitude and distance of the planets Mercury to Neptune over a period of several thousands of years to about 1 arcsecond of precision. They are intended for use by programmers desiring to make their own astronomical computations programs.
Can it do anything more than compute the presumed heliocentric elements?
I downloaded it and read the following from the about page:
These Visual BASIC program modules form a nucleus around which to build a
sophisticated planetary ephemeris program.
They compose the essential subroutines to compute the heliocentric, ecliptical
coordinates, L, B and R according to the full VSOP87 theory.
Nothing about running it into the future and then converting to positions in the sky.
VSOP is based on
Astronomical Algorithms. I discussed this book in the
NOAA Solar Calculator page on the wiki. We know that Astronomical Algorithms is calculating R, the AU, for the planets under the heliocentric model, and some other elements, but then it stops there. The NOAA Solar Calculator Excel Worksheet, that is based on the same Astronomical Algorithms book, shows that the "Sun Rad Vector (AUs)," which is the distance between the the Earth and the Sun and the same as R, doesn't do anything, and is only an output value. It can be deleted from the worksheet entirely and the computations still work -- truly a demonstration of what
Astronomical Algorithms is all about.
Where is the part about converting the heliocentric model to what is seen in the sky and accuracy of planet positions?
If the above software package is based on the
complete VSOP theory, as it claims to be, then neither the description or about page shows that VSOP does anything more than calculate what the presumed heliocentric elements are.
I have also read that VSOP isn't even really converting to a real heliocentric model, but I will put that aside for now and come back to it later.