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lessn048.msg
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1996-11-15
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76 lines
************************* ELLIPSES ************************
\
THE ELLIPSE FUNCTION IS ONE OF THE GEOMETRIC SHAPES THAT CAN
BE GENERATED. LET US SELECT THE FUNCTION "ELLIPSE" FROM THE
CONSTRUCTION AREA MENU.
<end>
THE DEFAULT OPTIONS OF "CE 1P" (CENTER TO ONE POINT) AND
"ISOMT" (ISOMETRIC ELLIPSE) ARE PRESELECTED. WITH THE
CURRENT SETTING LET US DRAW A GREEN ELLIPSE FROM ITS CENTER
TO ONE POINT ON THE CIRCUMFERENCE USING "CE 1P".
<end>
THE OPTION "ISOMT" REFERS TO THE RATIO OF MAJOR TO MINOR
AXES OF THE ELLIPSE. THE RATIO OF MAJOR TO MINOR AXIS CAN
BE SET AS DESIRED USING THE OPTION "RATIO".LET US SELECT IT.
<end>
A POINT HAS BEEN SELECTED ON THE SCREEN WHICH CORRESPONDS TO
THE INTERSECTION OF THE TWO AXES. FIRST WE SHALL SET THE
SIZE OF THE MAJOR AXIS BY MOVING THE CURSOR AND ACTIVATING
IT ANYWHERE ON THE SCREEN.
<end>
NEXT LET US MOVE THE CURSOR AND ACTIVATE IT TO SET THE SIZE
OF THE MINOR AXIS. IF THE MINOR AXIS IS MUCH SMALLER THAN
THE MAJOR AXIS THE ELLIPSE APPEARS MORE AS A CIGAR SHAPE.
<end>
THE RATIO HAS BEEN SET. "ISOMT" HAS BEEN AUTOMATICALLY
TURNED OFF. LET US DRAW AN ELLIPSE USING THE "CE 1P" OPTION.
<end>
LET US CREATE OTHER ELLIPSES WITH DIFFERENT RATIOS.
<end>
TO RESET THE RATIO TO ISOMETRIC SELECT "ISOMT".
<end>
THE OPTION "1P CE" (1 POINT TO CENTER) DRAWS THE ELLIPSE
FROM A POINT ON ITS CIRCUMFERENCE TO THE CENTER. LET US TRY.
<end>
THE OPTION "ARCS" LETS US DRAW ARCS OF ELLIPSE BY CLIPPING
THE DESIRED PORTION OF THE ELLIPSE AND ERASING THE BALANCE.
LET US SELECT "ARCS" AND DRAW AN ELLIPSE
<end>
THE ELLIPSE REMAINS IN THE COLOR WHITE. TWO LINES RADIATE
FROM ITS CENTER. PLACE THOSE LINES ON THE SCREEN AND THE
COUNTERCLOCKWISE PORTION OF THE ARC BETWEEN THE TWO LINES
REMAINS ON THE SCREEN AND THE BALANCE IS ERASED.
HERE IS THE FIRST LINE.
<end>
HERE IS THE SECOND LINE.
<end>
THE COUNTERCLOCKWISE PORTION OF THE ELLIPSE REMAINS.
<end>
"CPYEL" (COPY ELLIPSE) IS A VERY USEFUL OPTION THAT RECALLS
THE RATIO, SIZE AND THE ROTATION OF THE LAST ELLIPSE AND
MAKES A COPY OF IT.
<end>
LET US SELECT "CPYEL".
<end>
NOW ACTIVATE THE CURSOR ANYWHERE ON THE SCREEN.
<end>
A COPY OF THE LAST ELLIPSE APPEARS. IT CAN NOW BE PLACED
ANYWHERE ON THE SCREEN.
<end>
THE OPTION "CPYAR" (COPY ARC) PROVIDES A COPY OF THE LAST
ELLIPSE AND LETS US CLIP THE PORTION OF THE ELLIPSE THAT WE
WOULD LIKE TO KEEP.
<end>
AT ANY TIME THE ON-LINE HELP IS AVAILABLE FOR REFERENCE BY
PRESSING THE KEY "H" OR "?" WHILE IN ANY FUNCTION.
<end>
THE OPTION "CENTR" PLACES A SMALL CROSS AT THE CENTER OF
THE ELLIPSE FOR REFERENCE.
<end>
THE OPTION "UNDO" ERASES THE LAST ELLIPSE.
<end>
THE OPTION "CONCN" DRAWS CONCENTRIC ELLIPSES.
<end>
*********************** END OF LESSON **********************
<end>