?
Solved

How to know curve direction?

Posted on 2002-06-03
10
Medium Priority
?
203 Views
Last Modified: 2010-04-06
Dear experts,

There is a closed cutve consisting of 12 x,y points. How can I know that curve is in clockwise or anticlockwise direction?

Please help me. It's urgent.

Thanks.

0
Comment
Question by:mansan
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 3
  • 2
  • 2
  • +2
10 Comments
 
LVL 30

Expert Comment

by:weed
ID: 7051440
Look at the graph points. If you have to, plot them on paper in the order theyre in.
0
 

Author Comment

by:mansan
ID: 7052908
Hello weed,

Yes, by plotting the curve on paper I can know the curve direction, but I'm making a project in c++ to convert a 2D image in 3D. In that I'm facing this problem so I need a  routine to know curve direction.

any idea?

Thanks.
0
 
LVL 30

Expert Comment

by:weed
ID: 7052918
Ahhh...gotta specify stuff like that in the question.
0
On Demand Webinar - Networking for the Cloud Era

This webinar discusses:
-Common barriers companies experience when moving to the cloud
-How SD-WAN changes the way we look at networks
-Best practices customers should employ moving forward with cloud migration
-What happens behind the scenes of SteelConnect’s one-click button

 
LVL 2

Expert Comment

by:shlezman
ID: 7053298
The alorithm goes like that you'll have to figure out how to implement it, sorry
1. connect the dots.
2. draw a vertical line to the one of the segments.
3. if the vertical line crosses the curve odd number of times to the right then it's a clockwise, if it crosses odd number of times to the left, it counterclockwise.
       ______
      /      \
    ^ |------|----
      \______/

the ^ shows the real direction
the ---- line is the vertical line
sorry for the too simplified drawing.

good luck
0
 
LVL 3

Expert Comment

by:TheRedGuy
ID: 7056472
Surely this is a question of perspective on the curve itself? How can one say whether a curve is going in a particular direction? Unless of course the order of the twelve co-ordinates dtermines the direction but you have not stated this!!

If that is your intention, then can you not simply take account of the co-ordinates that you are plotting? For a 2D curve, if

x is increasing, while y is decreasing
OR
x is decreasing and y is increasing

then you are plotting in a clockwise direction, while if

x is increasing while y is increasing
OR
x is decreasing while y is decreasing

then you are plotting in an anti-clokwise direction.

Having said that, the question of whether either x or y is increasing or decreasing would be relative to the origin of the curve!

I think you need to explain a little more what you are after!

btw, is this a homewrok question???
0
 
LVL 2

Expert Comment

by:shlezman
ID: 7057117
I guess it is homework or some kind of riddle on graphics and polygons.
This sounds like a very well known and basic polygon algorithm, assuming curve=polygon otherwise there is no meaning to direction.
The polygon can take any closed shape and it's line can cross itself like the number "8", there are two ways to describe a polygon with the shape of "8", very much like writing it, for example if you start writing it from the bottom point, you can continue to the right or to the left. If you continue drawing to the right you'll get counterclockwise description, continuing to the left will get you clockwise shape.
Hope it was clear.
0
 
LVL 84

Accepted Solution

by:
ozo earned 150 total points
ID: 7060360
The sum
 y0*x1-y1*x0
+y1*x2-y2*x1
+y2*x3-y3*x2
...
+y10*x11-y11*x10
+y11*x0 -y0 *x11
will be positive for clockwize points, and negative for counterclockwize points,
assuming thr curve does not intersect itself
0
 

Author Comment

by:mansan
ID: 7061500
Hi ozo,

This method is really working. But when I compute, sum is positive for counterclockwise & negative for clockwise.
0
 
LVL 84

Expert Comment

by:ozo
ID: 7063273
Sorry, I got x and y mixed up.
0
 

Author Comment

by:mansan
ID: 7063784
Ozo Thanks for your help.
0

Featured Post

Free Tool: Port Scanner

Check which ports are open to the outside world. Helps make sure that your firewall rules are working as intended.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Keep your audience engaged and get the most out of your next presentation with these quick Prezi tips.
Many programs have tried to outwit PowerPoint in terms of technology and skill. These programs, however, still lack several characteristics that PowerPoint has possessed from the start. Here's why PowerPoint replacements won't entirely work for desi…
HTML5 has deprecated a few of the older ways of showing media as well as offering up a new way to create games and animations. Audio, video, and canvas are just a few of the adjustments made between XHTML and HTML5. As we learned in our last micr…
Add visuals to your Prezi to keep your audience engaged. Learn how to embed images, edit them, and more in this video micro tutorial. Select "Insert" from the top menu in your Prezi editor: Select "Image": A toolbar will pop in from the right …
Suggested Courses

762 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question