On Tue, 06 Nov 2012 09:35:46 -0800 mathog <mathog@...1176...> wrote:
Maybe I am old fashioned but I just don't understand the problem. For as long as I can remember scale drawings said in the legend something like "1 inch per foot" or "1 inch per mile", or whatever. In Europe it was probably "1 cm per meter", which is even easier. Then the person making the drawing, and the person reading it, would just replace one unit for the other in their head - 10 was inches on the drawing, but feet in the real world. Which was pretty easy to do so long as it was 1 of these for 1 one of those, and only slightly harder if it was 1:5 or some other ratio.
The "units.txt" file specifies "3.543307" as the conversion factor between millimetres and "px", the unit used internally. Does this ratio meet your criteria for "only slightly harder"? Have you ever seen a drawing which specified a scale of "3.937008 inches per metre" (otherwise known as "1:10")?
I think the OP has quite adequately explained the problem:
As a user of metrics it really is mindnumbing to have to work with 3.543307 px per mm. I'd much rather would set that to 10 or 100 for instance so I can more easily work from px units into mm and vice versa. I guess that for those that use their feet to do measurements 90dpi makes more sense though they must have some trouble when it comes to fractions of Inches (what pinky's?). If I want to design something in metrics and I get all those fractioned numbers in my files, it makes it a tad difficult to edit it by hand or script. Especially the latter is rather important for me.
In any case, your analogy is inaccurate. You will recall that engineering drawings of the sort you are describing, in addition to the scale being specified in the legend, have all the most important dimensions explicitly marked on the drawing itself, and these are ALWAYS specified in terms of real-world dimensions, and are NEVER adjusted by the scale factor of the drawing. The idea that a drawing of a machine part, or building, designed in imperial units, would be dimensioned in metric, or vice-versa, is too absurd to merit further comment.
The direct analog of the scale specification you are referring to, is the zoom factor setting which appears in the lower-right corner of the Inkscape window, not coincidentally the same position as the scale on a paper drawing. Nobody is suggesting getting rid of this; we are merely asking that the explicit dimensions in the drawing be expressed in terms of appropriate real-world units, as they invariably are for a paper drawing. Why should the measurement information available from a drawing produced on a 3GHz 64-bit computer be inferior to that produced with a ruler and pencil on a sheet of paper?
The document being produced by Inkscape is a drawing, and it will never be at actual scale for microscopic or macroscopic objects. If it was it wouldn't be possible to print the drawing without scaling it up or down.
If you were looking at a road map, and the distance between New York and Los Angeles was specified as "427.3 mm", would you regard that as acceptable? Or would you conclude that the people who drew the map were idiots?
This has always been true of drawings of actual objects, except in a few extremely rare instances where full scale drawings are produced (like masks for chips or spray painting templates).
Templates for wooden frames or steel plates in shipbuilding, body panels for cars and other sheet-metal work, and cloth panels for sails, tents, clothing, and hot air balloons, also come to mind, although many of these processes probably now use computer-driven laser cutters, so that no paper drawing is needed at all.
It seems safe to assume that when reduced-scale design drawings were made for these objects, any explicit dimensions were specified using real-world units.
Would not some sort of "sticky" comment that reflected the drawing to represented object length ratio suffice to address this "problem"?
That's what the zoom setting box is for, and it's not constant, because one of the advantages of a computer over a piece of paper is that you can easily adjust the visible/physical scale ratio.
I also addressed this issue here:
http://sourceforge.net/mailarchive/forum.php?thread_name=20121104003312.162f...
http://sourceforge.net/mailarchive/attachment.php?list_name=inkscape-devel&a...
And other people addressed it here:
http://wiki.inkscape.org/wiki/index.php/BlueprintGeometricAndTechDrawing
http://wiki.inkscape.org/wiki/index.php/BlueprintRealUnit
I note that these proposals are marked "priority: essential" and "priority: high", respectively.
-- Ian Bruce