The Computer's Coordinate System

[anonymusflasher]

Why is the coordinate system in computer graphics, in general, have their
coordintates vertically reversed? I remember that Cartesian coordinate systems
had the positive y-axis going UP but in computer graphics it's goes DOWN.
:confused; Why is that?

[*]

The zero point for both the X and Y axes is the upper left corner of the screen.
positive increments move right and down. Just like reading a book from the upper
left corner, across the page, then down to the bottem right hand corner. They
could move negatively, left and up, but may move off screen if they pass 0 in
both planes.

[v_teo]

simple : the 0 point of the y axis is in the top-lef corner of the monitor, rather than the bottom-left.

[Motion Maker]

Yes, thankfully the system is reversed, y increases as you go down the
screen and decreases as you go up. Same with x.

Also in Flash since this is a Flash forum

The stage (visible part of a movie) is 0,0 in the top left corner and
Symbols register 0,0 in their middle to allow for positioning center points
relative to others.

--
Lon Hosford
www.lonhosford.com
May many happy bits flow your way!
"v_teo" <webfor...@macromedia.com> wrote in message
news:dkj152$lcj$1...@forums.macromedia.com...

[mspres]

Perhaps I'm just dense, but both replies above mine just don't seem to answer
the question. Why is my right hand on the opposite side as my left hand? 1)
Because your right hand is on the right side of your body and your left hand is
on the left side of your body. 2) Thank goodness this is true, right is
opposite of left and left is opposite of right, and dogs paws are like this to.

Seriously, I'm just as curious now why differ the system's coordinate plan
from a long established cartesian coordinate system. It doesn't seem to offer
any advantages and since most people are familiar with the cartesian system, it
actually impedes those educated to such.

[*]

On Sun, 6 Nov 2005 02:35:22 +0000 (UTC), "mspres" <webfor...@macromedia.com>
wrote:

CRTs draw a picture to the screen from left to right, top to bottom, starting at
the upper left corner. My guess is that would be the reason for the XY origin
being in the upper left corner. Because a CRTs electron gun will never have to
draw "off screen", there isn't a need for negative numbers.

[Motion Maker]

My response was geared towards the intent of the forum being about Flash and how it works.

 

"The stage (visible part of a movie) is 0,0 in the top left corner and
Symbols register 0,0 in their middle to allow for positioning center points
relative to others."

 

To go further you also will find in the Symbols the ability to change the registration point to any corner.

 

As to the search for computer coordinate systems consider these statements from  Craig Andera

" Simply put, a coordinate system is just a way of describing points in space. There are many different possible coordinate systems – you may have heard of Cartesian coordinates, spherical coordinates, cylindrical coordinates or others. ... the three-dimensional left-handed Cartesian coordinate system. It identifies points in three dimensions using an x, y, and z coordinate. All of the axes are perpendicular (properly speaking I should say orothogonal) to each other. The x coordinate increases horizontally to the right. The y coordinate increases vertically upward. And the z coordinate increases “into” the screen, away from the viewer. This last bit is important – most scientific and engineering textbooks that you might have used in school usually use a right-handed coordinate system, where z increases towards the viewer. In computer graphics, this is reversed to give a natural meaning to coordinates – the z value now becomes a measure of how far away something is. "

 

It appears to me Cartesian had limitations or others had advantages based on many links that come up with a simple Google search.

--
Lon Hosford
www.lonhosford.com
May many happy bits flow your way!

"mspres" <webfor...@macromedia.com> wrote in message news:dkjq5a$l1n$1...@forums.macromedia.com...

[Tom Unger]

mspres;
Consider that page size is variable. Perhaps it was in part based on a
coordinate system long ago established by the postscript language (print
graphics) which placed the origin in the upper left corner of the
-Tom Unger