AND IN AUTOLISP?
there are no built-in lisp functions to do coordinates conversions
you can either use Map's api or write your own functions
I know programming in Autolisp not know Topography. I need the formulas and datum conversion if already in better Autolisp.
Datum Projection is very complex.
UTM zone is divided into several like utm-39N, utm-34S, utm-52N.......(refer attached image file)
Each zone has own projection parameters(7 or 4 parameters).
but you can easily project coordinates on autocad map3d or autocad civil...not autocad.
(defun proj (fproj tproj point)
;fproj:original projection
;tproj:to projection
;point: list of coordinates
;ex: (proj "UTM84-15N" "LL84" (list xxxxxx.xxxx xxxxx.xxxx))
(ade_projsetsrc fproj)
(ade_projsetdest tproj)
(ade_projptforward point)
)
This is projection function on autocad map3d.
And if you want to make your function, refer map projection library in other language.