Adding dimensions to an isometric view.

simon_powell

Is it possible to show dimensions on isometric views? Onshape allows me to do so and it seems to be in the correct plane, but the dimension stated is smaller than it actually is. My guess is that it's a result of showing a 3D dimension in 2D?

viru

@simon_powell, Actually it is due to foreshortening property of isometric view. Please refer below detail.
The concept of foreshortening is a very important one in isometric projection. Let us take two orthographic views (first angle i.e elevation above) of a pencil which is parallel to the ground, and take a view perpendicular to its length. In its starting position the pencil is a true length in both plane and elevation. Holding the pointed end of the pencil steady move the opposite end away from you, ensuring the pencil remains parallel to the ground. Keep moving the pencil away from you until you are looking along the point of the pencil. A view along the point of the pencil (a point view) is a view parallel to the direction in which the pencil is pointing. The length of the pencil changed as you moved it from full length to a point view. Every time you moved the pencil away from you its length appeared to get shorter or it foreshortened. As the pencil rotates parallel to the Horizontal plane its elevation becomes foreshortened. The further you move the end of the pencil away from you the greater the foreshortening. This is known as the degree of foreshortening. For example, if you moved the pencil from its starting position (full length) 5º away from you (the 5º is relative to the vertical plane) then the degree of foreshortening is very small as the pencil appears only a little smaller than full size. However, if you moved it 85º from its initial position then it would appear very small (very near a point view). In this case there is a large degree of foreshortening.

Note: The pencil is initially parallel to both the Vertical and Horizontal planes. It is then rotated 5º . The pencil is now no longer parallel to the Vertical plane. The full 5º rotation can be seen in the plan view. When fully rotated the pencil is perpendicular to the Vertical plane and still parallel to the Horizontal plane.
Let us take the same cube as above to further illustrate this point. Starting with an elevation view of the cube we see a square. The LOS, in this view, is perpendicular to the front edges e.g. 'AB' and 'BC' and also to the back edges e.g. 'EF' and 'HG' ('G' is the lower corner right behind 'C' in the elevation). Because the LOS is perpendicular to these edges, they are true lengths. It is also important to note that in the elevation edges 'AE', 'BF', 'CG' and 'DH' all appear as point views. This is because we are looking parallel to these lines.


Let us now rotate the cube about 'AD' so that the elevation and end view are visible together. We are no longer looking perpendicular to the front face of the cube. What has happened to the edges 'AB' and 'AE'? The line 'AB' has been rotated just like the pencil above so it appears shorter in this view, i.e. 'AB' has foreshortened. However, the line 'AE' has gone from being a point view to a line view. This line still does not appear as a true length so it is still foreshortened. How about line 'AD'? We are still looking perpendicular to this line so it appears as a true length.

Finally let us rotate the cube vertically up about the line 'DG' while holding point 'D' on the ground. Now, what has happened to line 'AD'? Well, we are no longer looking perpendicular to it so it now also has foreshortened. If you watch the animation you will see the vertical height of line 'AD' decrease. In fact, all the edges of the cube now appear foreshortened. If the angles between the projection of the axes are equal, i.e. 120º, then all the edges foreshorten equally. This view is known as an isometric view. When the cube has been fully rotated a point view of the body or long diagonal 'DG' results which only occurs in an isometric view of a cube.

Narayan_K

simon_powell , You are correct it is showing 2D dimension.Isometric value will be less than the normal value.It will shorten the length by 81.65 %. So if you measure center to center in Isometric view it will show 816.5(1000 x 0.8165).

simon_powell

viru

@simon_powell, Actually it is due to foreshortening property of isometric view. Please refer below detail.
The concept of foreshortening is a very important one in isometric projection. Let us take two orthographic views (first angle i.e elevation above) of a pencil which is parallel to the ground, and take a view perpendicular to its length. In its starting position the pencil is a true length in both plane and elevation. Holding the pointed end of the pencil steady move the opposite end away from you, ensuring the pencil remains parallel to the ground. Keep moving the pencil away from you until you are looking along the point of the pencil. A view along the point of the pencil (a point view) is a view parallel to the direction in which the pencil is pointing. The length of the pencil changed as you moved it from full length to a point view. Every time you moved the pencil away from you its length appeared to get shorter or it foreshortened. As the pencil rotates parallel to the Horizontal plane its elevation becomes foreshortened. The further you move the end of the pencil away from you the greater the foreshortening. This is known as the degree of foreshortening. For example, if you moved the pencil from its starting position (full length) 5º away from you (the 5º is relative to the vertical plane) then the degree of foreshortening is very small as the pencil appears only a little smaller than full size. However, if you moved it 85º from its initial position then it would appear very small (very near a point view). In this case there is a large degree of foreshortening.

Note: The pencil is initially parallel to both the Vertical and Horizontal planes. It is then rotated 5º . The pencil is now no longer parallel to the Vertical plane. The full 5º rotation can be seen in the plan view. When fully rotated the pencil is perpendicular to the Vertical plane and still parallel to the Horizontal plane.
Let us take the same cube as above to further illustrate this point. Starting with an elevation view of the cube we see a square. The LOS, in this view, is perpendicular to the front edges e.g. 'AB' and 'BC' and also to the back edges e.g. 'EF' and 'HG' ('G' is the lower corner right behind 'C' in the elevation). Because the LOS is perpendicular to these edges, they are true lengths. It is also important to note that in the elevation edges 'AE', 'BF', 'CG' and 'DH' all appear as point views. This is because we are looking parallel to these lines.


Let us now rotate the cube about 'AD' so that the elevation and end view are visible together. We are no longer looking perpendicular to the front face of the cube. What has happened to the edges 'AB' and 'AE'? The line 'AB' has been rotated just like the pencil above so it appears shorter in this view, i.e. 'AB' has foreshortened. However, the line 'AE' has gone from being a point view to a line view. This line still does not appear as a true length so it is still foreshortened. How about line 'AD'? We are still looking perpendicular to this line so it appears as a true length.

Finally let us rotate the cube vertically up about the line 'DG' while holding point 'D' on the ground. Now, what has happened to line 'AD'? Well, we are no longer looking perpendicular to it so it now also has foreshortened. If you watch the animation you will see the vertical height of line 'AD' decrease. In fact, all the edges of the cube now appear foreshortened. If the angles between the projection of the axes are equal, i.e. 120º, then all the edges foreshorten equally. This view is known as an isometric view. When the cube has been fully rotated a point view of the body or long diagonal 'DG' results which only occurs in an isometric view of a cube.

Narayan_K

simon_powell , You are correct it is showing 2D dimension.Isometric value will be less than the normal value.It will shorten the length by 81.65 %. So if you measure center to center in Isometric view it will show 816.5(1000 x 0.8165).

simon_powell

Thanks a lot for the responses! Explained it really well.

NeilCooke

Simon - you can also override the dimension and enter the actual value if you need to show the dimension on the isometric. 

michael3424

Is there any reason why OS could not calculate and display dimensions on isometric views?

3dcad

I've struggled with this for decades, the best view to show furniture dimensions to people would be single 3d view with all needed dimensions. And the best way to create that view would be 3d cad so that I can easily get new version if dimensions change (ie. not overiding any dimensions).

Foreshortened values in drawings seems pretty redundant? Does anyone have any use case where this value is needed instead of actual lenght from the 3d model?

SquidLord

3dcad said:

Foreshortened values in drawings seems pretty redundant? Does anyone have any use case where this value is needed instead of actual lenght from the 3d model?

It's not the fact that the length calculated for an isometric view is hard. Geometrically it's actually quite simple. The real problem runs thus:

There is literally no way to tell the difference between an isometric view and an orthographic view on a flat sheet of paper.

Literally, that is the problem. You cannot tell whether a projection is 3-D or 2-D once it's projected onto a 2-D surface. Take a look at the dowel example. Is that illustrating one dowel laying parallel to the plane of view and the same dowel at an isometric retreating angle or is it illustrating two dowels, one parallel to the plane of view and the other also parallel to the plane of view with a non-orthographic cut across both ends? You can't tell. It is literally impossible to tell.

That's why the basic assumption in 2-D mechanical drawing is that any part measured is parallel to the 2-D viewing plane. Because without that assumption, you simply cannot understand what you're seeing in any part of the illustration. That has to be a key part of the assessment of said drawings.

The best way to show furniture dimensions to people is actually an interactive 3-D view with the dimensions hanging out in 3-D. There are a couple of CAD programs which are exporting to an active PDF file which essentially do that, and Fusion 360 allows you to give view access to an online interface to view the model live. Honestly, in Onshape there's no real reason not to give people a link to an assembly derived into its own document if you want to show off a particular piece of furniture with all of its dimensions but without showing all of "your work." It would be nice if we could create a view which actually showed those dimensions attached to the model as it's rotated and moved, and I'd love to see that, but it's definitely not necessary.

3dcad

So I need to forget 2d drawings and hunt for named views with possibility to show certain dimensions - this is something I have requested before we even had 2d drawings in Onshape

brian_brady

SquidLord said:

3dcad said:

Foreshortened values in drawings seems pretty redundant? Does anyone have any use case where this value is needed instead of actual lenght from the 3d model?

It's not the fact that the length calculated for an isometric view is hard. Geometrically it's actually quite simple. The real problem runs thus:

There is literally no way to tell the difference between an isometric view and an orthographic view on a flat sheet of paper.

I hear you and you are correct, about a drawing on paper. An Onshape drawing is not on paper. OS knows that the view you are asking to connect a dimension to is actually an isometric view and thus should be able to give you isometric dimensions. I would like to see isometric dimensions myself. To make it work, there would probably need to be a new dimension tool. Sometimes the only way to get the isometric dimension you want would be from a surface to a vertex and that is not currently an option.

david_weber318

I have looked at the whole thread here and understand.  I also agree that this has been a problem in all the CAD programs I have used.  I would like to make a formal request a tool/method  to make Isometric Dimensions  possible and easy.  Thanks!

Jake_Rosenfeld

@david_weber318

https://forum.onshape.com/discussion/8519/support-of-drawing-dimensions-in-oblique-views-true-dimensions

erik_bongers

Perhaps this is a standard, and thus has nothing to do with OnShape, but...what on earth could be the use of these foreshortened dimensions?
Please help me explain these sizes to my carpenter.
This is mindblowingly weird.
Wait a minute...when I google "dimensions in isometric drawings", I get loads of examples with REAL dimensions, so...this is just a bug in OnShape?

PeteYodis

@erik_bongers

No this is not a bug in Onshape drawings.  This is just functionality we have not implemented yet.  We will get to it.  Right now Onshape only places projected dimensions.  This is generally the more popular use case compared to true dimensions.   As others have mentioned there is not an automatic way to know that dimensions should be "true" versus projected.  We will likely include a setting on a view that will set dimensions to be true or projected.  It's likely that isometric views will always be set to True type when we implement this, and then users can switch if they need.  For named views, it will probably be impossible to know if users want true or projected dimensions by default so we will likely default to projected.  We will likely not permit, at first, for views to contain a mix of true and projected dimensions.  That can get awfully confusing to the readers of drawings.  

ifan_lappage537

This works in Autodesk Inventor, I guess they take the dimensions from the 3D model, the software seems to know this and is not dimensioning a flat 2D representation. I really want to use Onshape for education purposes, so that the drawing can be given in isometric, students are not given the answer, when they are asked to produce a drawing in orthographic. little anomalies like this put me off. The whole debate about true and projected dimension should not exist, the object created is the size it is, the dimensions should reflect the size of the object.

steve_shubin

I am not a programmer. Not my thing.

BUT, I do believe, that without too much effort on the part of Onshape employees, we could have a half decent workaround, where there are 3D dimensions in the Drafting tab

Just one thing needs to be done — HAVE AN OPTION to hide lines created with the USE tool. 

Now I don’t want to suppress these particular lines. I just want to hide them. And I don’t want to suppress them because I want to use the dimension tool on these lines to get my 3D dimensions.

THAT’S ALL THAT NEEDS TO BE DONE !

Once you have your dimensions, all you need to do is take a screen capture and paste that into the drawing tab

——————————————————

There are a couple other things that would improve on this. One such thing would be to have an option to make the driven dimensions black upon doing a screen capture

The other thing would be for Onshape to create a tool or function for doing VECTOR screen captures (Vector PDF) where I could then paste that into the drawing tab

Take a look at the PDF below

steve_shubin

OK if you downloaded the PDF above, you saw that we have 3D dimensions in Onshape RIGHT NOW.  Not the full blown 3D dimensions, but a workaround

But, to make those 3D dimensions, you have to use the USE tool on the surfaces that you want to create the dimensions. When you use that USE tool, it makes a very heavy weight line. That’s why I would like the ability to hide those lines made with the USE tool

steve_shubin

I could be wrong as I am a greenhorn on the browser version of Onshape, but yesterday I stumbled across what seems to be that you can only use SHOW DIMENSIONS on one sketch at a time on the browser version of Onshape.

On the mobile version, or at least on my iPhone, I could use SHOW DIMENSIONS on as many sketches as I want, and have all these different sketches SHOW DIMENSIONS simultaneously. Which gives me that ability to do what I did in the above PDF.

Not realizing that you could not do this on the browser version — well that’s maybe why I got that dastardly down vote - LOL

Anyway, it seems that the iPhone or the mobile version of Onshape has something that the browser version doesn’t

GO MOBILE !

randy_young

@ Pete Yodis -  You assert that this is "generally the more popular use case" and as such, Onshape considers this to be working as intended.  I have scratched my head for the better part of an hour to find a SINGLE legitimate use case for this projection of a mathematically constructed "measurement" that has no relation to the physical object modeled.  Maybe I'm missing it but since you claim it's so common, can you illustrate a few uses in which this number would be beneficial if not necessary for the end user rather than the  true measurement?  I'm not trying to be rude, but I'm just not seeing any reason and your explanation seems like a cop-out to me.  I'm happy to be proven wrong though.  Maybe I'm not getting it.

PeteYodis

 This is not a bug as I've mentioned in a post above - it's simply just not implement by us yet.  Furthermore, blocking projected dimensions on views is not a good endeavor without first supporting true dimensions because there are many shapes that users might model that have no discernible "isometric" orientation.  So we do what we can at this point in time.  Many of us intend for Onshape to be more than what it currently is, but Rome is not built in a day and we let our users see the new best state of Onshape every 3 weeks.  

Projected dimensions are most definitely the more used dimensions on drawing views in general.  Yes, not for isometric cases, but in general they are used far more extensively in engineering drawings for lots of good reasons  - compared to true dimensions.  

alexander_visakay

Hello all, I am also trying to dimension an isometric view to give to my students so that they can draw parts from my drawings. If I am understanding correctly this is not a function of OnShape yet?

NeilCooke

Correct

alexander_visakay

NeilCooke said:

Correct

Thank you

Any suggestions?

NeilCooke

Orthographic projections?

alexander_visakay

NeilCooke said:

Orthographic projections?

  Yes that is what I have been giving them and what I want them to turn in on their drawing sheets. I just don't want to give them the entire answer all the time. 

pierre_jay019

Agree with @steve_shubin. The problem would easily be solved by :
- Allowing "show dimensions" on multiple sketches at a time on the Desktop app
- Allowing to hide lines created with "use" functions
I really hope the Onshape team will work on this feature

tim_hess427

alexander_visakay said:

NeilCooke said:

Correct

Thank you

Any suggestions?

Hand sketch?

onshaper

There should be a way to dimension isometric views. Without this feature, Onshape feels too terse for furniture specification. 

christian_petty

For anyone curious, ASME accepts dimensioning in axonometric views:

• ASME Y14.3-2012 r2018 Orthographic and Pictorial Views
• ASME Y14.41-2019 Digital product Definition Data Practices

seven_zero_three

This is frustrating. This behavior is practically equivalent to having the dimensions in a sketch alter as you zoom in and out on the screen.