[GRASS-user] preferred grid size

Glynn Clements glynn at gclements.plus.com
Sun Feb 18 19:08:34 EST 2007

Brent Wood wrote:

> >> is there any preferred grid size for creating topographic index map ?
> >>
> >> ( elevation map is produced from 1: 25000 scaled topographic map )
> >>     
> >
> >
> > [more of a thought experiment than actual educated advice]
> >
> >
> > PostScript points are 1/72", which equates to a thin line on a printed
> > page, about as small a feature as is useful in a hardcopy.
> I thought Postscript point/line widths vary, depending on the rendering 
> device resolution.
> eg: 300x300, to 2400x2400 etc.... 

A "point" is a unit of measurement used in typography, equal to
roughly 1/72" (historically, the precise definition has varied;
nowadays, the most common definition is exactly 1/72").

PostScript's default coordinate system uses points, i.e. a file
containing the following sequence of commands will draw a one-inch
filled square, exactly one inch in from the left and bottom edges:

	72 72 moveto
	144 72 lineto
	144 144 lineto
	72 144 lineto

You can change the coordinate system at will, but it starts out with
one unit equal to one point, and the initgraphics operator will reset
it to that scale.

The initial line width is one unit (i.e. 1/72" unless you change the
scaling). The current line width is stored in units, so if you change
the scaling the line width will automatically change by the same
factor. The physical resolution of the device doesn't have any affect
upon the default coordinate system or the default line width.

> so you can get a 1/2400" line if you really want it (not that anyone
> with normal vision could see it :-)

PostScript allows a line width of 0 to mean a single pixel line at the
device's physical resolution. However, apart from being too thin to be
of practical use, laser printers often cannot actually print anything
that small (the electrostatic printing process tends to inherently
perform "thinning" of the black areas), so even someone with
super-hero vision wouldn't be able to see it ;)

Glynn Clements <glynn at gclements.plus.com>

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