# Isometrics in Scale?

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If you create a rectangle that's 10 feet by 10 feet (in scale), and extrude it to 10 feet deep, creating a 10 foot cube, and then choose view, right isometric, you'll get something that looks like an isometric view of a cube.

But, if you measure a side with the tape measure tool, or print it out and use a scale ruler, you'll find that the sides actually measure 8 foot, 2 inches, in scale.

Why is this? Is there a setting to change this behavior so the isometric view measures 10', like the shape actually is?

The iso view does not project the full edge length onto the view plane. Only a "full face" orthographic view of a cube face, a view which shows only a square, without revealing any of the other edges or faces, will result in your measurements showing the native lengths of the cube edges.

But you do bring up, once again, the strong desire in the VW user community for easy 3d edge and 3d point-to-point measuring and annotating capability. You are welcome to add your voice to the others by posting your desire in the Wish List area of this forum.

-B

That is not what Isometric is. From Wikipedia.

Isometric projection is a form of graphical projection ? more specifically, an axonometric projection. It is a method of visually representing three-dimensional objects in two dimensions, in which the three coordinate axes appear equally foreshortened and the angles between any two of them are 120?. Isometric projection is one of the projections used in drafting engineering drawings.

As Benson said, we "all" wish for dimensioning in isometric views, but it is not there yet.

Pat

For the 30? isometric dimension > use tan0.707106781=35.26438968?

scale factor = cos35.26438968... = 0.816496580928

• 1 month later...

OK Islandmon, enlighten my math. I've been using a ratio of .8135 derived emperically by measuring objects of known dimension in plan view in the isometric view and calculating this observed ratio.

I fully comprehend that the resulting foreshortening should be mathematically calculable in theory but where do you derive the 35.etc angle that you used.

Which gets to my isometric dimensioning workaround. I make a separate layer for dimensions and change the layer scale for the dimension layer to account for the foreshortening,e.g. dimension 1:48 drawing on a 1:59 layer. Now that I know the secret formula I will set the dimensioning layer to 1:58.7878 (i.e. the reciprocal of the cosine times the drawing scale - 1/0.81649658 * 48 = 58.7878). This works famously as long as you get your sheet visibility stuff worked out to show the dimensions over the part of the drawing your working on (it also shows that my empirical figure of 59 was a pretty good rule of thumb).

The last difficulty to work out is I can't make head nor tales of snap to object while doing this. It seems to work in some cases and not in others. I need help figuring out how the hell you input dimension values directly.

What I've been doing is making a dimension and then if it doesn't come out to my known calculated dimension in the style of drawing I'm doing I can usually just limit the precision of the dimension to force it to the length I want. This is different than actually measuring objects in three dimensions. It is noting on a three dimensional drawing measurements I already know and wish to quickly communicate. My desire is to be able to make quick isometric views with basic dimensions on them for building projects and ideas. I just want the drawing to put them in instead of printing it out and having to write the dimensions on. Call me retentive.

I can't figure out how the hell to set the default precision on the dimension tools which would save me having to go back each time and make it easier to draw the dimension in the first place.

More importantly, life would be much easier if I could enter the parameters for the dimension directly in the cursor bar above the drawing. I have read several threads that say you start drawing a dimension and hit tab. This takes you to direct input in the bar. Got it. Done that, but I put in numbers and have tried hitting the tab again, the return key, going back and clicking the drawing thinking that the entry will force the next mouse click. Nothing, these direct entry numbers won't take.

And to make matters worse there is no way to adjust them after the fact using the same parameters that were used at creation that I can find. What kind of craziness is it that all the numbers used to create the dimension don't show up in Object Info palette where I could change them!? Anyone who could explain to me how to make my entries into the info/cursor bar at the top of the drawing and/or find a window where I could edit a dimension through keyboard entry afterwards I would be grateful.

In case it makes a difference, I usually am trying to set the length and angle of the dimension. Obviously I set the angle to the skew of the isometric. The length I want to set to my know length. Because the isometric view does not put up the drawing in a way that starts in from the origin in a way that preserves x,y coordinates from plan views, I can't readily enter my starting location and ending location. Instead I click on the drawing where I want to start and then try to enter a length (meaning the dimension length, not the change in x, change in y, there is a separate box for the length) and the angle.

Thanks and hope that this workaround might be handy for folks like me looking to create quick dimensions on a three dimensional view, if not for those actually trying to measure three dimensional drawings to a great degree of precision.

Brian

I fully comprehend that the resulting foreshortening should be mathematically calculable in theory but where do you derive the 35.etc angle that you used.

Isometric Projection uses 30? , 35.26438968?.

1/sqr2=0.707106781 , 1/tan(0.707106781)=35.26438968?

cos(30?)=0.866025403, cos(35.26438968?)=0.816496581

Arctan(0.707106781...) = 35.26438968...? { arctan ≠ 1/tan, 1/tan = cotan }

1/Sqrt(2) or 1/√2 = 0.707106781... { your sqr2 looks like 2 squared - may be confusing to some }

also cos(45?) = sin(45?) = 0.707106781...

so Arctan(cos(45?)) = Arctan(1/√2) = 35.26438968...?

etc.

The devil is in the details.

Raymond

" The last difficulty to work out is I can't make head nor tales of snap to object while doing this. It seems to work in some cases and not in others. I need help figuring out how the hell you input dimension values directly. "

VW have a problem currently - have reported it last year November and according Tech are the engineers still working on it, and also the problem when you attach for example a rectangle to be extruded to a 3D object and you adjust the size in the OIP and it moves off the position you have locked it to. It is a heck of a accuracy problem in VW 13 but not VW 12.

I was speaking more theory of ops. I see the math gives the answer. The question is why is the arctan of the sq.rt. of two the angular ratio that defines the foreshortening.

while the horizontal draws at 30 degs on the isometric, I assume the reason that the ratio between a horizontal line drawn in plan and isometric view isn't simply 2 to the sq. rt. of 3 is because the angle of view also involves a z angle as well. You're looking from an angle above the drawing as well as at an angle that shows both the x and y vertical plane.

So there is maybe some additional foreshortening I'm that doesn't figure just from the cosine ratio of a 30 deg. angle.

So, I'm still looking for a description of what the 35 and change angle.

Why is the reciprocal of the sq. rt. of two the tangent of the angle whose cosine defines the ratio of plan to isometric drawing?

thanks,

brian

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