Measurement of pdf Underlay - Snapping versus Not Snapping

[Jeff10]

Hi,

I've been using pdf underlays for a while. I generally don't have problems inserting at a correct scale that allows the drawing output from AutoCAD to be measured / scaled correctly.

I have run across a problem recently on two projects that are causing me to scratch my head. One resulted in measurements that caused problems with bidding estimates.

I am taking pds and inserting them as underlays. I am scaling them to 1/2 the original pdf drawing scale. I normally insert a pdf into model space using a viewport in paperspace. Next I zoom extents. Then zoom 1/1xp to see how the underlay fits in the viewport. The problems I am having are with when I zoom to 1/2xp to reduce the size of the underlay in the viewport.

The problem is measuring lengths while in paperspace.

Here is a screen shot when I use the distance measurement tool and don't snap to any geometry on the pdf.

And the following is the distance measurement when snap to geometry on the pdf (which I am still in paperspace)

What is causing the different measurements?

It makes sense that I am off by a factor of 2; but, I'm not aware of any variables that can be changed.

Any ideas?

Thanks,

Jeff

[paullimapa]

Could you share this dwg along with pdf for us to take a look?

[Jeff10]

Hi Paul,

Is there a way I can do that privately as opposed to posting them on the forum. They are customer drawings and I can't take any liberties with them. I hope you understand.

And just thinking out loud, is there a variable that I'm overlooking? When I snap to geometry on the pdf it is measuring the distance as if the pdf was inserted a 1:1, rather than 1:2.

Please let me know about the files.

Thanks,

Jeff

[paullimapa]

I just messaged you

[paullimapa]

FYI, this is typically what I do when I attach pdfs into a dwg. I would attach into Model tab and make sure the objects measure at full scale which is 1 unit = 1 inch (in your case it's Imperial units). If it's a floor plan I would look for a typical door width and scale the entire PDF based on that typical door width of 36". If it's site plan, I would look for a parking stall and scale the pdf based on the typical parking stall width of either 9' or 10' wide and etc.

Of course that means I'm drawing everything else in Model in full scale also.

Then in Layout I would setup my Paper Space Vports with the Display Scale I want to plot. Now everything including the attach PDF in Model should reflect the same scale as all the drawn objects there.

[Jeff10]

Hi Paul,

Although I inserted the pdf in a viewport in model space (rather than inserting it directly into the model tab) the scaling is correct with the underlay.

Here is a screen shot of the measurement in model space

This shows the same distance measurement as in my first post when I am in paper space and use the distance tool and snap to geometry in the pdf.

Another check of the measurement in paper space when snapping to geometry (ends of column references)

Another check of when I do not snap to the underlay geometry in paper space and just pick to points that are eyeballed off the same column lines

Maybe I am not doing a good job explaining this....

Something happens when I reference the pdf underlay, even in paper space, when the viewport has changed from 1:1... the measurement tool still thinks the underlay is at 1:1.

The problem that this creates is not being able to accurately measure from a pdf underlay in AutoCAD if the viewport is different than 1:1. Now, if I plot the drawing and use a scale to measure I would get the same distances as if I snap off the geometry of the pdf.

Sorry if I am making this complicated.

Jeff

[paullimapa · Accepted solution]

Again without access to your file it's difficult to see what you've done.

But if you attached the pdf at full scale based on the steps I provided then you won't have any problems.

For example, I've attached the Floor Plan sample.dwg file included in the typical installation of AutoCAD.

For the purpose of this demonstration I created Layout Letter 1-16 with a Vport's Display Scale as 1/16" and plotted a PDF that's scaled @ 1/16"=1'-0"

Then I PDFAttached the pdf into Model at scale of 192 (this reverses 1"=16' or 1"=16x12=192" scale back to full scale) on new layer 0-PDF

Next I moved the pdf into the same location over the plan drawing.

I copied Layout Letter 1-16 and called the new layout Letter 1-16 PDF.

For the sake of argument in layout Letter 1-16's vport I vplayer freezed the 0-PDF layer which is the layer I placed the pdf so that won't show up.

I then executed the DIST command eyeballing the measurement between grid lines between 4 & 3 and the result shows:

1 7/8"

Repeating the same process on layout Letter 1-16 PDF's Vport where the PDF does show up executing the DIST command eyeballing the measurement between grid lines between 4 & 3 and the result shows the same: 1 7/8"

So when the PDF is attached and scaled up to full scale in Model if your Layout's VPort is set also using the proper Display scale then and only then would everything be correct.

[cadffm · Accepted solution]

Hi,

Just to point out to "What is causing the different measurements?"

Without osnaps, you enter coordinates in paperspace (distance between two points on paperspace)

With osnaps, you enter coordinates in modelspace (distance between two points in modelspace),

and if dimassoc is set to 2, you associate your dimpoints to this modelspace object.

[Jeff10]

Hi Sebastian,

That's good information. I didn't understand that with osnaps the actual model space coordinates are being used. I wrongly assumed that while working in paperspace the coordinates would be the paperspace coordinates, not the modelspace coordinates.

I have experimented with different values for dimassoc and none seem to make a difference when snapping to the pdf geometry.

What is odd, also, is that sometimes when I use the dist command and snap to geometry on the pdf while in paperspace (with dimassoc set to 2) the result will be the correct paperspace distance. And then I reissue the command and the distance shows up as the modelspace distance. I can't really find a way to duplicate it, though. It's almost random. And in the middle of a project I don't have as much time to troubleshoot as I would like.

I guess I need to adjust my thinking.

Thanks for your input.

Jeff

[cadffm]

Hi,

"I have experimented with different values for dimassoc and none seem to make a difference when snapping to the pdf geometry"

Dimassoc is for dimension objects ONLY,

and has nothing to do with the displayed dim-value.

As you can read in the help [F1]

0 - create lines, mtext... instead of a dimension object

1 - creates non- associated dimension object

2 - creates associated dim2nsion objects if you use osnap and if the environment is as needed.

  For example: Dim a simple line and it will create a full associated dimenstion object.

Associated: Realtime link to an object.

Edit the libe, the associated dim will follow

[Jeff10]

Hello Sebastian,

Thanks for the clarification. 

I was confused with what you had stated above: "if dimassoc is set to 2, you associate your dimpoints to this modelspace object".

Because I had been talking about dist and measurement, and not dimensions, I thought that you were saying that dimassoc also affects the measurement.

It was my misunderstanding about the measurement of pdf underlays with snaps... that measurement will only reference the pdf and not the paperspace area.

Sorry for all the trouble.

Jeff

[pendean]

@Jeff10 TLDR but if you are cripplingly challenged about sharing actual PDF/DWG files here, open a support case with Autodesk if you are on subscription to seek out Autodesk Support's help:
https://www.autodesk.com/support/account/manage/use/support#:~:text=com/plans.-,Contact%20support,-S...

It appears to me you are assuming your PDF was generated at an actual scale and not 'fudged', a popular copyright-protection method used by many that need to share PDFs but don't want someone like you to gain free unpaid knowledge.

[Jeff10]

Hello Paul,

Thanks for your detail.

Thanks to Sebastian I understand that the snaps are actually coordinates, so the scale of the pdf insert matters if any type of measurement is being used with the drawing.

Even inserting the pdf according to scale would have made some tasks easier in the past. It's a best practice that I will follow in the future. Thanks for including it in your message.

Take Care,

Jeff

[Jeff10]

Hi Sebastian,

Thanks for the information about the snaps to the pdf in modelspace and actually making use of their coordinates. I should have known that; but, I didn't. Thanks for the information.

Jeff