On Fri, Jan 14, 2011 at 6:17 AM, Susan Spencer <susan.spencer@gmail.com> wrote:
crjw and John Culleton,

Your examples and information were fantastic and useful.

My biggest reason for using printer's points is to sidestep
the differences between Gimp's ppi/ppcm v. Inkscape's ppi/ppcm.
I use Gimp to clean up scanned images before working in Inkscape.
Many older patterns are exactly 1/4th scale, so the Gimp to
Inkscape workflow results in a bit of extra work.
Gimp uses 72ppi, Inkscape uses 90ppi for the time being.

As John pointed out, the value of 72.72 for a printer's point
is outdated.  So I did some research:

Printer's points, inches, cm's, mm's, etc. are reconverted
back to pixels by each rendering platform according to its
own ppi/ppcm definition.  So yes, they're always
accurate.

Also, Inkscape defaults numeric precision to 8,
and will pad numbers with 0's to match the precision
setting.

Wikipedia's page explains that 72.72 was set in 1886,
and was changed in 1959.
"...The desktop publishing point (DTP point) is defined as 1/72 of the
Anglo-Saxon compromise inch of 1959 (25.4 mm)..."

Still, Donald Knuth used 72.72 in Tex in the 1970's.
The inventors of Adobe PostScript used 72.

This discussion may seem overkill to some, but it
does make a difference, and thanks to everyone for
pointing out the precision issues.

- Susan



On Fri, Jan 14, 2011 at 3:47 AM, <inkscape-user-request@lists.sourceforge.net> wrote:
Date: Fri, 14 Jan 2011 05:50:38 GMT
From: "crjw" <crjw@irisnet.ca>
Subject: Re: [Inkscape-user] Inkscape Accurancy
 
<snip>
 
Consider the following:
 -a road map
 -a circuit board design
 -a floor plan
 -a sewing pattern
All of these drawings accurately reflect some physical entity.
Usually measurements or coordinates of the physical entity are known and
can be expressed in standard units such as meters, miles, inches, mils, etc.

My only reason for writing this post is to point out that it is possible
to enter coordinates into an SVG drawing in their native values... regardless of how big or how mall the unit is.
 
<snip> 
 
-crjw