On 06-Nov-2012 11:59, ian_bruce@...2136... wrote:
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")?
Internally Inkscape has a consistent drawing model, which is 90 dpi. The conversion you are referring to is the result of 90 dots per inch/25.4 mm/inch to give 3.543307 dots (pixels) per mm. Internally inkscape has all sorts of inch,pixel, and mm conversions, but they are all with respect to the fixed scale of 90 dpi.
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,
That is correct, although the units may be implicit at each label with the units explicitly marked in the legend, as in "All measurements in feet."
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?
The map will say "427.3" and the legend will tell me what the units are. I would interpret the map accordingly without regard to its actual size, as I may have a copy which has been enlarged or reduced in size relative to the "standard" map.
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.
Yes, and if one were going to make such a thing from Inkscape one would set the proper scale factor for the "printer" which was capable of such a large scale rendering.
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.
Right. I seem to be missing your point. A drawing of the USA is imported, a line with arrow ends is drawn from LA to New York and is labeled "3940". The legend says units are in miles. What exactly is Inkscape doing wrong here that needs to be corrected?
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.
The zoom setting box in this analogy is just a magnifying glass to be applied over the drawing. Looking through it would not change the labels. Using it does not affect the scale relationship between the drawing and the real objects represented in the drawing.
http://sourceforge.net/mailarchive/forum.php?thread_name=20121104003312.162f...
which says
I found that in order to fit the whole drawing on the screen at once, I had to set the zoom factor to 3% or less, which was inconvenient.
That sounds like you tried to draw it 1:1 at the internal resolution of 90 dpi. My screen is about 2 feet across and 2 *33.3 ~= 67 ft, which is roughly house sized. If you go into the the page setup and create a document which is 100ft x 100ft then you can use the "ft" setting elsewhere. Note however that what this has done is to create a drawing which is basically a 100ft x 100ft sheet of paper. When the cursor moves on that screen the pixel values are very large. When I did that using the Windows version zoom would not go below 1% so it was not possible to fit the entire drawing on the screen at once (close though). This approach is not the way to go, you might be able to squeeze in a house, but certainly not a battleship or a city.
There are a couple of things that might be helpful in constructing scale drawings. One would be a measuring tool which reads out in the "real world" coordinates instead of document coordinates. For instance, read the 50m diagonal length of a rectangle that was drawn at 30 meters by 40 meters by selecting opposite corners and using "measure". Another would be an external/internal scale factor ("1 foot per inch"), which would change the ruler units and coordinate units, both of which are always pixels no matter what the document settings has the drawing set to. (This is what I think you requested originally, more or less.) That wouldn't be very hard to do. Adding the same feature everywhere might be a bit of a challenge. For instance, in "Transform" one can set the shift value to "ft", but that is distance in the drawing, not in the represented object. That dialog would need to be modified if the scaled value was to be used instead.
True architectural drawing and CAD/CAM programs go a heck of a lot farther than just providing a document to represented object scale. Nowadays they detect nonphysical interactions (walls going through walls), produce lists of parts, draw objects from parts libraries, make 3D views, feed into engineering analysis programs, etc. Inkscape is just a drawing tool, and even if we give it a built in scale ruler (essentially) it will still be just a drawing tool.
Regards,
David Mathog mathog@...1176... Manager, Sequence Analysis Facility, Biology Division, Caltech