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In PostScript, each printed page has a default coordinate system consisting of an origin in
the lower left-hand corner of the page. There are 72 PostScript units to the inch, which
makes the PostScript unit very close to the standard printer's point (1/72.27 inch).
For our purposes, however, it is convenient to work in another coordinate system, namely, the
coordinate system employed by the user when he or she selects the Print command button.
For example,
suppose a twoD view window displays coordinates x, y and ranges
1#1,
2#2
and suppose that the Print Window is owned by this view
window. (The owner of the Print Window may be determined by examining the Owner message on the
Print Window. See the entry for the Print Window in the User's Manual.)
The default PostScript coordinate system is scaled so that the ranges
1#1,
2#2
fit in a square which is 500 PostScript units on a side.
(This number, 500, can be modified by changing the constant BBoxSide in the prologue file.
See Section 2.4 below.) The point (x0,y0) will be located at a
point approximately 3/4 of an inch to the right and 1.5 inches up from the
lower left-hand corner of the page. These values can also be customized.
Because of this scaled coordinate system, it is straightforward to modify PostScript files
which are written by dstool (provided the user knows a little bit about PostScript).
For example, if the user knows that a special bifurcation point occurs at
3#3
and wants to place a special symbol at this point, there is no need to convert
the coordinates of
3#3.
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root
1998-11-02