There's no standard formula for dimetric since it's not a standardized projection according to ISO. Most CAD programs allow it as a custom parallel projection with arbitrary angles. The old DIN here in Germany specifies 7 degrees and 42 degrees and shortening the depth axis by 0.5 while drawing the front lines to exact measure. That does, however, not yield a correct volume representation. You would have to calculate the exact foreshortening based on whatever angle you use for 7 degrees that's about 94%...
There's no standard formula for dimetric since it's not a standardized projection according to ISO. Most CAD programs allow it as a custom parallel projection with arbitrary angles.
I was hoping you wouldn't say that...
Don't misunderstand the above comments. Axonometric drawing is certainly not arbitrary. The angles (and their lengths) in axonometric drawing are not arbitrary relative to each other.
Look: Simple logic dictates that there is only one set of axis lengths/angles in isometric drawing because by definition isometric dictates that the three axes of your drawing space (represented by the three visible surfaces of the unit cube) are equally foreshortened (viewed at the same angle relative to the line of sight).
Dimetric and trimetric--again by definition--use two or three (respectively) differently foreshorened axes. So of course dimetric and trimetric drawing accommodates multiple orientations, because by locking only two (in dimetric) axes to equal lengths, you have allowed a variable--a freedom of movement (which is the purpose). But beyond letting you choose a range of orientations, there is nothing arbitrary about it. That is, for any given dimetric (or trimetric) orientation you may choose, there is still only one set of axis angles/lengths which are correct, and they do indeed "yield a correct volume representation." (They are every bit as mechanically proportional and accurate as isometric.)
What I'd really like, though, is the numbers I need to draw a dimetric illustration.
Much confusion can be relieved by understanding that isometric, dimetric, and trimetric are actually drawing methods, not drawing types. Technically, whether you are drawing in isometric, dimetric, or trimetric, the result is a mechanically-correct orthographic projection. Isometric, dimetric, and trimetric are just practical and expedient methods by which to achieve it.
Even while you are working on what you think of as an "isometric illustration," if you get serious about it at all, you'll eventually encounter objects or parts of objects which are not so conveniently oriented parallel to your isometric drawing axes, and you'll have to know how to properly construct them. After all, not everything in the world is box-shaped and neatly stacked and aligned parallel or perpendicular to each other. Thankfully, the world is more interesting than flat images on the sides of a cereal box. That's the basic misconception of those who think isometric drawing is nothing more than just a few scale/rotate/skew tricks.
Consider this: Imagine drawing in isometric a set of three todler's building blocks. One of them is rotated somewhat about one of your isometric axes. One of them is rotated about two of your isometric axes. When done, ask someone whether it is an "isometric drawing," a "dimetric drawing," or a "trimetric drawing." Guess what...you can't really tell by looking at the drawing because if done correctly, the drawing would be identical regardless of which of the three methods you used.
As for standards, long before personal computers, there were (still are, actually) drafting templates specifically set up for particluar dimetric and trimetric orientations. The particular orientations were chosen for practical reasons: versatility in the sense of usefulness, and ease of execution in terms of the tools at hand (for example, the click stop increments of drafting machines).
You used the fateful word - "calculation" - that stops me in my tracks every time. My mathematical abilities are horrendous.
You just need to get over that. There is nothing to fear about axonometric drawing. The basic calculations involved are grade-school trig functions that can be done on the calculator provided with your computer, and can be understood in a matter of minutes. And the construction can be done interactively, without using math. (Again, that's part of the reason for the method.)
Either show a sketch of a cube that depicts the dimetric orientation you want, or state the angle you want to use for the left or right axis, and I'll give you "the numbers" to make a set of Actions for it similar to the ones from the 2009 thread.
Thanks for that.
I really need to take the time to look in to the process and the maths involved and whatnot and work out how to calculate it all myself when I get the chance.
In the meantime, however, "the numbers" would be hugely, hugely appreciated.
This is one I found online that looks good to me.
And, if I'm not mistaken, the angle is 17 degrees.
A thousand thanks, in advance.