Re: link areas within images

Kevin Altis (
Thu, 24 Jun 1993 10:44:59 -0800

>I agree with Robert's call for the more traditional lower-left-based
>coordinate system, but feel obliged to point out that the X Window
>System has 0,0 at the upper left.

Since, this issue doesn't want to die, I vote for staying with "0,0" at the
top,left. Except for PostScript, that is the common usage within character
based and bitmap based displays. Diverging from this practice now will
require extra transformations to the local text and graphics environments.
PostScript can be confusing sometimes because of the 0,0 at the bottom,
left. Think about large objects that span pages and arbitrary scaling of
objects where the "anchor" is typically at the top left of the object, not
at the bottom left. Even in the simplest cases, where there isn't a "page
boundary", drawing occurs from the top left, then down the virtual page,
with scrollbars added if needed. With Hebrew, Arabic, Kanji, etc. which
read right to left, you still start at the top of the page.

It would be possible to put "0,0" at some arbitrary location within an
image, like the center of the image so that you have the image overlayed on
a "normal" cartesian coordinate system. It requires a transformation as
simple as putting "0,0" at the bottom left, plus defining where you want
"0,0" and whether you want positive y to go up or down, prior to
referencing any images.