Re: LOGO-L> ellipse

[rimpey@netspace.net.au (Richard Impey)]

Sorry there was a slight error in my previous messages

Please note that I had changed Georges procedure from ellipse to ellipse1
so as not to conflict with Jeff's
ellipse.

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

>>Unfortunately I couldn't get either George's or Jeff's  ellipses working
>>with MicroWorlds v2 for the Mac.
>>I tried different combinations of values for 'rad_x' and 'rad_y' but had
>>the same error messages.
>>
>>George's.....
>>
>>In the command centre I entered.........
>>
>>                        ellipse1 40 40
>>
>>and the error message was.......
>>
>>                        I don't know how to repcount- in ellipse1
>>
>>Jeff's.......
>>
>>In the command centre I entered.........
>>
>>                        ellipse 20 40
>>
>>and the error message was.......
>>
>>                        size*:eccentricity has no value in ellipse
>>
>>
>>xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>>
>>Georges CORRECTED procedure follows.....
>>
>>to ellipse1 :rad_x :rad_y
>>>;
>>>; There are several methods to describing an ellipse,
>>>; this is just one of them and I prefer it because
>>>; it's easy to conceptualize its size and calculate
>>>; points that are exactly tangent.
>>>;
>>>; However, this is probably not the best method for
>>>; describing elliptical trajectories.
>>>;
>>>make "orig_x first pos               ; Save current turtle pos x
>>>make "orig_y last  pos               ; Save current turtle pos y
>>>pu                                   ; Get to first point on ellipse
>>>                                     ;   without drawing
>>>repeat 361                           ; Sweep through 0 - 360 ~
>>>   [
>>>   make "ang repcount-1              ; For clarity create an
>>>intermediate
>>>                                     ;   variable
>>>   make "x :orig_x-(sin :ang)*:rad_x ; Calculate New X coord
>>>   make "y :orig_y-(cos :ang)*:rad_y ; Calculate New Y coord
>>>   if :ang = 1 [pd]                  ; If we are already on the ellipse
>>>                                     ;   then put the pen down
>>>   setxy :x :y                       ; Draw a line segment
>>>   ]
>>>pu                                   ; Pen up for the trip back to the
>>>                                     ; center of the ellipse
>>>setxy :orig_x :orig_y                ; Restore original pos
>>>; I'll leave it as an excercise to allow the ellipse to be rotated
>>>; according to the turtles heading as MSWLogo's ellipse does
>>>end
>>>
>>xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>>
>>Jeff's procedure is as follows...
>>
>>to ellipse :size :eccentricity
>>make "n 0
>>repeat 360
>>[rt :n fd :size lt :n lt :n fd :size*:eccentricity rt :n make "n :n+1]
>>end
>>xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>>
>>
>>What am I doing wrong?
>>
>>Cheers Richard
>
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>
>                        Richard Impey
>                        Assistant Principal (Acting)
>                        Learning Technologies and Art Specialist
>                        Phone 0011 61 3 9509 6872
>                        Caulfield North Primary School
>                        186 Balaclava Road
>                        Caulfield North 3161
>                        Melbourne, Victoria, Australia
>
>
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                        Richard Impey
                        Assistant Principal (Acting)
                        Learning Technologies and Art Specialist
                        Phone 0011 61 3 9509 6872
                        Caulfield North Primary School
                        186 Balaclava Road
                        Caulfield North 3161
                        Melbourne, Victoria, Australia


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