Topocentric Primary Directions are based on the actual rotation
(where Transits, Progressions, Directions, etc. are based on the
revolution of the Earth around the Sun) of the Earth. In roughly 6
hours’ time virtually all aspects for the entire life will have formed.
This system is especially noteworthy, though it is to note that tiny
changes in the birthtime make great changes in when aspects would
mature. In other words, this is another one of those techniques
where a very precise birthtime is required; but likewise this feature
is also one of the reasons it makes a great “fine-tuning” mechanism
for honing in a much more exact birthtime.
It’s important to contrast these with normal primary directions,
because there are two fundamental differences. The refinements in
the calculation method, which come from Carl Kühr, are crucial.
Secondly, for the cusps to be the powerpoints they are, they will
require the usage of topocentric houses.
Topocentric Primary Directions are not supported by many
astrological programs or online calculation apps.
Polaris [free] - Isaac’s rectification program. (32-bit Win XP)
Astro [free] - Alexander Marr’s old program. (DOS)
Placidus [expensive] - Rumen Kolev’s traditional astro program.
Online calculator - https://carta-natal.es/direcciones-primarias.php
(in Spanish, but there are other language options)