| | |
creating a ellispse at any aspect angle
![]() |
•
•
•
•
Originally Posted by aviral82
hi all ,
i have to create an ellispe the inputs are
major axis , minor axis , and the angle of the major axis
the ellipse needs to be tilted.
thanks
aviral
Construct the formula for the ellipse in standard position, and then use an affine transformation to rotate it. Better yet, if you need to draw it to screen, construct the parametric formula for the ellipse and transform that.
A circle in standard position is given thus:
x = r cos(t)
y = r sin(t)
t = 0..1
Change it to an ellipse by substituting the major and minor axes into the position of r in the x and y equations:
x = r_maj * cos(t)
y = r_min * sin(t)
Then multiply by the transformation matrix
[ [ cos(a), sin(a)] [-sin(a), cos(a)] ]
To rotate the whole thing counterclockwise by angle 'a'.
<r_maj*cos(t), r_min*sin(t)> * [[cos(a),sin(a)][-sin(a),cos(a)]] =
Which, after tedious and error-prone-when-done-by-hand matrix multiplication, gives
x = r_maj*cos(t)*cos(a) + r_min*sin(t)*-sin(a)
y = r_maj*cos(t)*sin(a) + r_min*sin(t)*cos(a)
This is just a quick answer; there are probably better and faster ways to get the points on an ellipse, but this'll definitely draw the right shape. If you're drawing pixel-by-pixel the line may look a bit chunky in places, since you'll be simply painting every pixel <x, y> ever occupies for 0<=t<=1. There are probably algorithms extant to smooth that behavior out and produce better "single-pixel-wide" lines.
![]() |
Similar Threads
- CS Major troubles/Confidence (Computer Science)
- issue with Tkinter canvas widget (Python)
- memory management in wndows 2000 (Windows NT / 2000 / XP)
- problem in creating a rectangle at a angle (C++)
- maths for 3d? (HTML and CSS)
Other Threads in the C Forum
- Previous Thread: text to numbers, numbers to text
- Next Thread: NEED HELP ON TOPIC : "INTELLECTUAL PROPERTY & HR EXPERTISE DATABASE IN S/W COMPANY"
| Thread Tools | Search this Thread |
adobe api array arrays binarysearch calculate char cm convert copyanyfile copypdffile cprogramme createcopyoffile createprocess() csyntax directory dynamic feet fflush file floatingpointvalidation fork forloop frequency getlasterror givemetehcodez global graphics gtkgcurlcompiling hacking hardware highest homework i/o inches incrementoperators intmain() iso kernel kilometer km linked linkedlist linux linuxsegmentationfault list locate logical_drives loopinsideloop. match matrix microsoft motherboard mqqueue mysql oddnumber odf open opendocumentformat opensource openwebfoundation owf pattern pdf performance pointer posix power probleminc program programming pyramidusingturboccodes read recursion recv recvblocked repetition research scanf scheduling segmentationfault send shape socketprograming socketprogramming stack standard strchr string suggestions systemcall test unix urboc user variable voidmain() wab win32api windows.h






