| 
January 2nd, 2009, 04:19 AM
| | Newbie | | Join Date: Jan 2009
Posts: 2
Country: Thanks: 0
Thanked 0 Times in 0 Posts
| | Translating a polygon Consider there is a polygon and a point P within the polygon. When the polygon is translated ( rotated or transformed to a new position or both) then the point should also be translated with respect to the new polygon position.
Can anyone figure it out. Thanks in advance | 
January 2nd, 2009, 04:57 AM
|  | MHF Contributor | | Join Date: Dec 2008 Location: South Coast of England
Posts: 1,561
Country: Thanks: 108
Thanked 881 Times in 764 Posts
| | Translation Hello nevetha Quote:
Originally Posted by nevetha Consider there is a polygon and a point P within the polygon. When the polygon is translated ( rotated or transformed to a new position or both) then the point should also be translated with respect to the new polygon position.
Can anyone figure it out. Thanks in advance  | I don't understand the question here. Can you re-phrase it?
In a translation, a polygon is moved to a new position in such a way that all points on the polygon move the same distance in the same direction, so that the new shape (the image) has exactly the same orientation as the original shape (the pre-image).
In a rotation, all points of the pre-image are rotated through the same angle about a fixed point - the centre of the rotation. Thus the polygon keeps its shape and size, but not its orientation (unless, of course, the angle of rotation is 360 degrees).
In a reflection, the lines joining corresponding points on the image and pre-image are parallel, and their mid-points lie on a straight line perpendicular to these lines. This is the 'mirror-line' of the reflection. The image is congruent to the pre-image but is opposite in 'sense'; in other words, if you move clockwise around the perimeter of the image, then you'll move anti-clockwise around corresponding points of the pre-image.
Rotations, translations and reflections (and any combination of them) are called isometries, because the image is congruent to the pre-image. But the word transformation may be used to denote other types of operation in which the image and pre-image are not congruent; e.g. stretching, shearing, etc.
So I think we need a bit more information about what is being asked here.
Grandad | 
January 4th, 2009, 10:57 PM
| | Newbie | | Join Date: Jan 2009
Posts: 2
Country: Thanks: 0
Thanked 0 Times in 0 Posts
| | Precise Okay let me be clear.
There is a polygon. U need to either translate or rotate it.
I need this for a computer based imaging system. The polygon is drawn with the help of mouse randomly.
There is a point inside the polygon. Now am able to translate the polygon using some pre-defined options. But there is no provision for translating the point(within the polygon) and hence it has to be done manually by coding. So what should we do to move the point to its new position with respect to the shifted polygon | 
January 5th, 2009, 05:56 PM
| | MHF Contributor | | Join Date: Apr 2005
Posts: 3,301
Thanks: 291
Thanked 1,160 Times in 1,062 Posts
| | Quote:
Originally Posted by nevetha Okay let me be clear.
There is a polygon. U need to either translate or rotate it.
I need this for a computer based imaging system. The polygon is drawn with the help of mouse randomly.
There is a point inside the polygon. Now am able to translate the polygon using some pre-defined options. But there is no provision for translating the point(within the polygon) and hence it has to be done manually by coding. So what should we do to move the point to its new position with respect to the shifted polygon | Apply whatever transform you are doing to the polygon to the point itself. | | Thread Tools | | | | Display Modes | Linear Mode |
Posting Rules
| You may not post new threads You may not post replies You may not post attachments You may not edit your posts HTML code is Off | | | All times are GMT -7. The time now is 06:33 PM. | | |
 | |  |