[MWForum]Elliptical orbits for planets

[Dale Reed]

>From my Logo1.doc at http://groups.yahoo.com/group/LogoForum/files/ :

<snip>
"The Great Logo Adventure" by Jim Muller specifically for the free MSWLogo
but also useful for newbies learning other kinds of Logos. The book is out
of print but sometimes it can be found in used bookstores or online at:
http://www.softronix.com/logo.html
http://groups.yahoo.com/group/LogoForum/files/
at http://www.algo.be/logo1/liens.html#livres under the 'The Great Logo
Adventure' section.
TGLA is also at http://www.educa.fmf.uni-lj.si/logo/doc/discover.htm in PDF
format.
<snip>

Chapter 8,  page 192

TO ELL :X :A :B :INC
IF (:X * :X) > (:A * :A) [STOP]
IF :X = :A [MAKE "INC -1]
SETPOS LIST :X :INC * :B * SQRT (1 - (:X * :X) / (:A * :A))
ELL :X + :INC :A :B :INC
END

TO ELLIPSE1 :A :B
ELL -:A :A :B 1
END

TO INFO
; CHAPTER 8 TURTLE POSITIONS AND COORDINATES
; ELLIPSES
; THIS PROCEDURES DRAWS AN ELLIPSE AROUND THE TURTLE'S
; POSITION (FROM THE CENTER).
;;
PR [SEE THE INFO PROCEDURE FOR MORE INFORMATION.]
END
============
TO ELLIPSE2 :S :E
MAKE "N 0
REPEAT 120 [RIGHT :N FD :S LT :N LT :N FD :S * :E RT :N MAKE "N :N + 3]
END

TO INFO
; CHAPTER 8 TURTLE POSITIONS AND COORDINATES
; ELLIPSES
; ELLIPSE2 STARTS AT THE EDGE OF THE ELLIPSE AND
; DRAWS THE FIGURE BASED ON YOUR INPUTS. USE SMALL
; NUMBERS; FOR EXAMPLE, ELLIPSE2 2 3.
;;
PR [SEE THE INFO PROCEDURE FOR MORE INFORMATION.]
END
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$ dale-reed@att.net    Seattle, Washington USA $