Path: news.mathworks.com!newsfeed-00.mathworks.com!solaris.cc.vt.edu!news.vt.edu!elk.ncren.net!newsflash.concordia.ca!canopus.cc.umanitoba.ca!not-for-mail From: Walter Roberson <roberson@hushmail.com> Newsgroups: comp.soft-sys.matlab Subject: Re: how to draw an arc between two points given centre and radius Date: Tue, 30 Mar 2010 14:41:08 -0500 Organization: Canada Eat The Cookie Foundation Lines: 30 Message-ID: <hotk4m$hl8$1@canopus.cc.umanitoba.ca> References: <hotir8$8a8$1@fred.mathworks.com> NNTP-Posting-Host: ibd-nat.ibd.nrc.ca Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Trace: canopus.cc.umanitoba.ca 1269978070 18088 192.70.172.18 (30 Mar 2010 19:41:10 GMT) X-Complaints-To: abuse@cc.umanitoba.ca NNTP-Posting-Date: Tue, 30 Mar 2010 19:41:10 +0000 (UTC) User-Agent: Thunderbird 2.0.0.24 (X11/20100317) In-Reply-To: <hotir8$8a8$1@fred.mathworks.com> Xref: news.mathworks.com comp.soft-sys.matlab:621996 Chanpreet wrote: > how to draw an arc between two points given centre and radius on matlab If you are given the two points, and given the centre and radius, then you cannot always do that. The distance from the centre and each of the points define radii, and if those two radii are not equal or are not equal to the given radius, then you cannot draw a circular arc. The circular arcs that pass through any two given points define a line. If the centre is not on that line, you cannot do what you ask. Only one coordinate of the centre would need to be given, and the radius would not be needed. If, alternately, the radius were given, then that would narrow it to one of exactly two points, and the only reason the centre would need to be given would be to distinguish which of the two points it was. Did you have something different in mind, such as a non-circular arc? Perhaps a parabolic arc, and the centre is really the focus? Anyhow... You can use arctan to find the sector angle to be drawn. Be sure to check in case you are crossing over the periodic boundary, as you probably want to draw the smaller of the two arcs. Then, knowing the angles involved, linspace() the angle range into an appropriate number of points, and then the points of the arc are [radius * cos(theta_range) + x of centre, radius * sin(theta_range) + y of centre)]