Up: Strageties for using scripts

Handling Coordinate Systems

The Geometry Center has developed a Perl module containing a number of subroutines for handling coordinate systems, axes, etc.

Download axes.pl

To use this library in your own Perl scripts, you must include the library in your script as shown:

#!/usr/local/bin/perl

require "axes.pl";
.
.
.

Subroutines in `axes.pl`

`gifsize`

Calling Syntax:

&gifsize(xmin, xmax, ymin, ymax, xmid,
ymid)

xmin, xmax are the minimum and maximum pixel values in the x direction of the region you wish to control. This region may be a "window" within the image.
ymin, ymax are the minimum and maximum pixel values in the yof the region you wish to control. This region may be a "window" within the image. Note that typically computer graphics coordinates go "down", so the "minimum" has a lower numerical value than the "maximum".
xmid, ymid are the pixel coodinates of the user coordinate system.

You must call gifsize before any other axes.pl routines, except pssize.

You can determine the gif coordinates of a region in a gif by using the middle mouse button in xv.

`pssize`

Calling Syntax: &pssize(xmin, xmax, ymin, ymax)

xmin, xmax are the minimum and maximum PostScript coordinate values in the x direction of the region you wish to control. This region may be a "window" within the image.
ymin, ymax the analogous values in the "y" direction. Note that programs like xfig typically scale the coordinate system so virtical coordinates go "down", so the "minimum" has a lower numerical value than the "maximum".

You must call pssize before any other axes.pl routines, except gifsize.

`sizetofit`

Calling Syntax: &sizetofit(xmax, ymax)

xmax, and ymax are the maximum values of your data in the first quadrant. Note:Both xmax and ymax must be positive. .

This routine chooses the user coordinate system so that the input point lies in the first quardrant region determined by the axes, which are in turn implicitly determined by the gif coordinates of the origin and the bounding box specified in gifsize>. The routine may srhink the user region more than is necessary to accomodate the input point to achieve better tick marks.

This routine requires that gifsize be called first. pssize can be called after, but none of the coordinate conversion routines involving PostScript coordinate will function until pssize called.

`u2p`

Calling Syntax: (px, py) = &u2p(ux, uy)

ux, and uy are the user coordinates of the point.
px and py are the returned Postscript coordinates.

`p2u`

Calling Syntax: (ux, uy) = &p2u(px, py)

px, and py are the PostScript coordinates of the point.
ux and uy are the returned user coordinates.

`u2g`

Calling Syntax: (gx, gy) = &u2g(ux, uy)

ux, and uy are the user coordinates of the point.
gx and gy are the returned gif coordinates.

`g2u`

Calling Syntax: (ux, uy) = &g2u(gx, gy)

gx, and gy are the gif coordinates of the point.
ux and uy are the returned user coordinates.

`p2g`

Calling Syntax: (gx, gy) = &p2g(px, py)

px, and py are the PostScript coordinates of the point.
gx and gy are the returned gif coordinates.

`g2p`

Calling Syntax: (px, py) = &g2p(gx, gy)

gx, and gy are the gif coordinates of the point.
px and py are the returned PostScript coordinates.

`xticks`

Calling Syntax: &xticks()

This routine attempts to intelligently draw and label tick marks on the x-axis. You will probably end up editing this routine to meet your own specifications.

`yticks`

Calling Syntax: &yticks()

This routine attempts to intelligently draw and label tick marks on the y-axis. You will probably end up editing this routine to meet your own specifications.

Up: Strageties for using scripts

The Geometry Center Home Page

Comments to: webmaster@geom.umn.edu
Created: May 10 1996 --- Last modified: May 30 1996

Handling Coordinate Systems

Subroutines in axes.pl

gifsize

pssize

sizetofit

u2p

p2u

u2g

g2u

p2g

g2p

xticks

yticks