This article was inspired by post https://swym.3ds.com/#community:70/iquestions:88
Without intending to offend the original respondents it seems that some confusion may exist on this topic. It is hoped that this article will clarify the matter by demonstrating how the validated answer and the comment both contribute to an effective method.
Try this:
Open a new drawing with DraftSight (DS) Units set up to work in “Architectural” mode (feet (symbol: ' ) & inches (symbol '' )). DS will accept data in either 5'6” or 66 form (inches understood in the latter case).
In model space, draw a 1200 x 900 rectangle, dimension its length and breadth, and save it as “ImperialRectangle”. (It may be necessary to apply a larger “Xn Dimscale overall” factor in the “Properties palette” for the dimension text to be visible. Try 20 and adjust from there.)
Note that the numbers entered are interpreted as inches and shown in the dimensioning as feet (perhaps with zero inches since there are no inches remaining).
Open a new drawing with DraftSight Units set up to work in “Decimal” mode (Metric: where a plain number may be treated as meaning the number of millimetres, metres, or even kilometres).
In model space, draw a 1200 x 900 rectangle, dimension its length and breadth, and save the drawing as “MetricRectangle”.
Note that this time the dimensioning shows the numbers just as they were entered. For the current purpose those numbers will be treated as the number of millimetres.
It should now be apparent that the first rectangle represents a 1200” (100 feet) x 900” (75 feet) real-world object while the second represents a 1200 mm x 900 mm real-world object. It should be apparent too that the physical, real-world sizes of the two drawn objects described by their dimensions is significantly different (100 feet does NOT equal 1200 mm) even though the actual numbers entered were the same in each case. This is due to the different dimensional systems in which they were drawn.
DS uses the same number of drawing units to represent corresponding entities in each drawing because the NUMBERS are equal even though the drawings themselves represent objects of significantly different real-world size.
Cad systems just work with the raw numbers and algorithms within the program take care of their manipulation for dimensioning and other purposes according to the Units Mode Settings currently in use.
Now use Rabi's method (see comment to answer in link at top) to insert the imperial drawing into the metric one:
With the “MetricRectangle drawing active proceed as follows:
Zoom out, if necessary, to create some space in the model space work area.
Insert the stored “ImperialRectangle” drawing as a block with “Position” set to “Specify later” and remaining settings as they are. (You may need to ZOOM > FIT before you can see all the drawing.)
Place the inserted drawing in a position somewhere above and sufficiently well clear of the other to allow for dimensioning of the other edges of the inserted drawing.
(Note that DS shows the inserted rectangle at the same visual size as the imperial rectangle because the same number of drawing units (not real-world units) occur in each drawing.)
Explode the block.
It will be showing the original 100' x 75' dimensioning of that drawing.
Now dimension the other edges of that rectangle.
Because the current drawing is set up for working in decimal mode the dimensioning will show 1200 x 900 (mm understood because of the use of decimal mode).
BUT --- as discussed already, a length of 1200 mm is a MUCH SMALLER REAL-WORLD SIZE than 100' (1200”). It is only equal to about 3.937'.
So the imperial dimensioning has NOT BEEN PROPERLY CONVERTED to the needed dimensions in the metric system. It should be showing a length of 30480 mm if the same object is being shown in both dimensional systems otherwise the real-world, physical size is being significantly decreased.
It should now be clear that the dimensioning must still be corrected by either applying a scaling factor to each dimension in the drawing or, generally better and more efficient, by applying the scaling factor to the elements of the drawing itself.
Since 1” is an equivalent length to 25.4 mm, it should be apparent that THE INSERTED DRAWING MUST BE SCALED, BY A FACTOR OF 25.4 (as suggested in the first answer to the referenced post at the top) to increase the actual number of units in each element of the drawing so that dimensioning will then be correctly converted to the metric system and the object will retain its physical real-world size.
Rabi has described a very useful method of getting the original drawing inserted into the new drawing so we will build on that.
Insert a second copy of the block “ImperialRectangle” (The block already exists in the drawing at this stage) but this time set “Scale” to 25.4 and tick the “Apply uniform scale” box. (Place it to the right hand side of the other drawings so that the scaled drawing extends into currently unused drawing space.)
Zoom the display to find the newly inserted drawing and, if necessary, move it to a more convenient position.
The increased size of the drawing, due to the greater number of drawing units in each drawing entity, will now be evident.
If dimensioning is associative, the original imperial dimensions will automatically adjust to correctly show the much larger size in imperial terms -- but these can be ignored at this time as they no longer correctly describe the original object. (It may be necessary to apply a larger “Xn Dimscale overall” factor in the “Properties palette” for the dimension text to be visible. Try 500 and adjust from there.)
Explode the block and dimension the non-dimensioned edges of this rectangle. These are the dimensions that matter.
Now the dimensioning should show 30480 x 22860. These are the correctly converted values of the original imperial dimensions of 250' x 75'. All entities in the drawing that was originally drawn with Imperial settings have now been properly converted so that they will correctly relate to any other drawing done with metric settings.
With appropriate alternative scaling factors these principles may be applied to any conversion from one dimensional system to another and even between different base units in the same system (e.g. metres to millimetres).
A note: While dimensioning in this exercise has been included with the model a drawing being converted in this manner is better stripped of any dimensions and other text that might exist in model space before scaling the entities only. There is some advantage therefore in having all textual information, including dimensions, in sheet space rather than model space and or on separate layers from the entities themselves.
Readers may also find some value in reading the blog article at https://swym.3ds.com/#post:15230 .
[User of DS (Free) V1R3.1 x64 on Windows 7/64 Home Premium.]
5 Mar 2013, 22:50 (NZ standard time)
