PDF not printing to exact scale

[SuperCAD]

I'll apologize in advance if this has been covered, but I was shown a problem at work today and I'm completely stumped as to why it happens or how to fix it.

 

I had drawn a structure that was exactly 119" tall and exactly 381" long. It was all done in 3D, which we all know is something that AutoCAN'T isn't good at, and I made a PDF showing the elevations to give to our graphics supervisor for production. The sheet was plotted using the stock PDF driver at a plot scale of 1:1. The dimension lines were aligned perfectly with the geometry in AutoCAN'T.

 

After plotting, I had sent the PDF to graphics and they imported it into Adobe Illustrator and noticed something was off. The dimension lines weren't aligned to the geometry. When measuring the lines, the length between the dimension lines was exactly 119 x 381, but the geometry was measuring at 119.03 x 382.02. I had opened the PDF that I had made, turned off the line thickness, and sure enough the dimensions were not aligned like they were in AutoCAN'T.

 

We're on 2018 with the latest version of Adobe Acrobat at work, but I wanted to try it at home. I have 2017 at home and an older version of Acrobat. I made a PDF of a simple box and the problem was the exact same. Mind you, I'm using completely different plotter drivers too. By using different drivers I was able to get closer to being exact, but each one was still a little off. And it wasn't consistent. It was off more in the Y than in the X.

 

Any ideas what's causing this?

 

[maratovich]

The bottom line is that the PDF structure uses points
When you print inches, it converts inches to points. And a lot depends on the accuracy in the program for creating PDF.
1. Check your drawing - maybe you have set the rounding sizes in AutoCAD. In reality, they are not accurate.
2. Use metric units of measure, they work better when converting.

[SuperCAD]

1 hour ago, maratovich said:

And a lot depends on the accuracy in the program for creating PDF.

I've tried this with 5 or 6 different drivers for creating PDF files. The ones that came with AutoCAN'T and the ones that Adobe installs.

 

1 hour ago, maratovich said:

1. Check your drawing - maybe you have set the rounding sizes in AutoCAD. In reality, they are not accurate.

There is no rounding at all.

 

1 hour ago, maratovich said:

2. Use metric units of measure, they work better when converting.

I've tried that too and got the same results. For example, to keep the sizes similar, I drew a box at 3000mm by 9700mm (close to 119" x 381") and plotted at a 1:20 scale. The PDF actually measures as 3000.16 by 9699.84. It went up in height and down in width.

[SuperCAD]

After more investigating, it turns out the DPI settings needed to be increased. 600 was the default, with is great for printing plans, but not for producing graphics. Tried it at 1200, 2400, 4800 and 9600 DPI and each setting gave different results. 9600 DPI being the best, but still not 100% accurate (i.e. 95 inches measured at 95.002 in Illustrator).

[maratovich]

Just wondering - give an example dwg and pdf.

[SLW210]

How are you measuring the PDF? Since you would need to plot the PDF to accurately measure the PDF, is that scaled correctly? PDFs try to force a Fit to Page IIRC.

 

Illustrator is not the most accurate at measuring, either. How does the drawing look when Exported in other Vector Formats? Illustrator can import dwg and dxf.

I have zero problems using 3D in AutoCAD, including sending accurate 2D files to a WaterJet, Plasma, etc.

A drawing and sample file would help.

[SuperCAD]

All of the measuring is done either in Acrobat Pro or Illustrator. I have checked every possible setting that I can access, and there are no fit to page options selected. Every PDF is created at a 1:1 scale from paper space. The issue is when our graphics department has to import the PDF into illustrator to layout their images. They have to manipulate the geometry to get to the exact size they need.

 

This doesn't happen when sending DXF files out to our CNC machine since it's working directly off a CAD file format and it matches what we draw.

 

Here are two examples. One using the stock AutoCAN'T PDF converter at 600dpi, and a modified PC3 file at 4800 dpi. The 119 dimension is a match in both, but the 381 dimension is 381.03 at 600dpi, but 381 at 4800dpi. Both PDFs were created from a viewport in paperspace set to a 1:40 scale.

 

[eldon]

I am surprised that you are vexed by lengths of lines in a PDF file not being as accurate as they were in a vector environment.

 

The Portable Document Format never pretended to be precisely accurate, relying, as it did on an arrangement of black pixels.

 

All printed drawings should have the caveat "Do not scale"

[SuperCAD]

You're surprised that a discrepancy has been brought to my attention and I'm just trying to figure out what the answer or solution is? Why would that surprise you?

[eldon]

Because you seem to be using the discrepancy to berate AutoCAD (viz your spelling of AutoCAD)

 

And because you seem to be comparing two disparate systems that do not produce exactly the same answer.

[Dahzee]

I think a lot of the problem is to do with how the .pdf is being created and how Autodesk have implemented it. I remember using Trueview (the only Autodesk product I have used) to create a .pdf of a radius cornered rectangle and when you zoomed in to view the resulting pdf the radius corners weren't even touching the horizontal & vertical lines!

 

It is perfectly possible to create a .pdf exactly as the CAD file; I work in the printing & packaging industry and the .pdfs I receive, created using the right programs are always accurate.

 

I don't pretend to understand all the technicalities but Bricscad also suffers from the same problems as Autocad with size discrepancies and entities lining up.

To make matters worse in Bricscad, if you increase the dpi too high, text depending on its height progressively disappears from your resulting pdf completely!

 

This is unfortunate as all artwork for printing (all over the world) is now created using the pdf format and creating drawings for graphic designers to apply their artwork onto should be 100% accurate.

 

Personally I think because a pdf is so easy to create using a printer driver it has been treated as a second class format, which it most certainly isn't.

 

If you read Wikipedia's section on PDF you will see that it is a lot more complicated and feature rich than most people realise.

 

Exchanging information using PDF should be treated the same way as any other export format, i.e as accurate as the technology allows.

 

Sorry rant over.

 

Back to the issue of size, you can always import a .dwg or .dxf into Illustrator and that should do the trick.

[ammobake]

I've seen this before.  You can create a custom PDF plot style with higher DPI and it will help.

The Autodesk app store has some interesting PDF add-ons too that you might try.  Some can create interactive 2D and 3D pdf files as well.  But never tried it myself.

 

I've run into the issue of PDF formatting throwing in unwanted margins before but doesn't seem like that's the issue here.

 

Out of curiosity, are you printing to PDF from model space or are you printing a view in paperspace?

 

ChriS

[SLW210]

It is a combination of the nature of a PDF and/or Illustrator. Illustrator uses points for measuring and is much less accurate, that's why resolution helps, for a short explanation.

They should be using dxf or dwg.

[f700es]

On 6/5/2019 at 10:28 PM, SuperCAD said:

I had drawn a structure that was exactly 119" tall and exactly 381" long. It was all done in 3D, which we all know is something that AutoCAN'T isn't good at

Sidebar: Why isn't AutoCAD good at this?

[SuperCAD]

5 hours ago, eldon said:

Because you seem to be using the discrepancy to berate AutoCAD (viz your spelling of AutoCAD)

 

My dislike of AutoCAN'T is for many reasons. None of which are related to printing/plotting or PDF creation.

 

5 hours ago, Dahzee said:

Back to the issue of size, you can always import a .dwg or .dxf into Illustrator and that should do the trick.

 

We just tried that again this morning and the file crashed Illustrator. They have done DWG/DXF importing in the past, but there is so much additional work that has to be done to the file that it's not an efficient process. For us, at least.

 

4 hours ago, ammobake said:

Out of curiosity, are you printing to PDF from model space or are you printing a view in paperspace?

 

I've tried it three ways. Directly from model space, from paper space with a viewport, and from paper space using viewbase. All three options gave us different results, but all were generally the same result.

 

[maratovich]

1. I wrote to you earlier - attach an example. Why ignore?
2. The answer is simple - in Acrobat, the measurement is made on the external side of the lines, taking into account the line thickness.
In AutoCAD, the measurement in the middle of the line does not depend on the thickness.
And Acrobat takes into account the thickness of the line.
If you consider that you use the scale, then this leads to a 0.03

 

[rkmcswain]

On 6/5/2019 at 9:28 PM, SuperCAD said:

 

Any ideas what's causing this?

 

 

As everyone else is saying in general, a PDF is nothing but a digital print, and will never be as accurate as a vector CAD drawing. This is why it's fairly pointless to convert a PDF back to DWG, unless you just need some general geometry, say for a N.T.S. exhibit.

[SuperCAD]

3 hours ago, maratovich said:

1. I wrote to you earlier - attach an example. Why ignore?

 

Didn't mean to. I thought the examples I posted would have been sufficient. A DWG file was not necessary.

 

3 hours ago, maratovich said:

2. The answer is simple - in Acrobat, the measurement is made on the external side of the lines, taking into account the line thickness.
In AutoCAD, the measurement in the middle of the line does not depend on the thickness.
And Acrobat takes into account the thickness of the line.
If you consider that you use the scale, then this leads to a 0.03

 

That's not the issue. If you turn off the lineweight in Acrobat (Ctrl+5) you'll see that the dimensions are taken from the center of the line. When I use the measuring tool in Acrobat, the line thickness is completely ignored. The thickness is also ignored in Illustrator.

 

7 minutes ago, rkmcswain said:

...and will never be as accurate as a vector CAD drawing.

 

That's what I've gathered, but thank you for summing it up. That's all I needed for an answer. 

 

This is the easiest way I can think of to show what I'm talking about. The line on the left is the dimension line, and the lines on the right are the geometry that is being measured. The line thickness is turned off and you can see that they do not align.

 

What's even more hilarious about this whole issue is what's shown below. The dimension lines measure out to be exactly what they should be, but the geometry is off. You would think that if they were only going to hold one of the two, that the geometry would be the one to make correct and have the dimensions be slightly off.

[BIGAL]

I don't need to do it but why not use import DXF it will use real numbers so 140.000000000 will be read.The only gotcha was must be an early autocad dxf.

[RobDraw]

On 6/5/2019 at 10:28 PM, SuperCAD said:

It was all done in 3D, which we all know is something that AutoCAN'T isn't good at

 

 

What?! Where are you getting this information from? There are many examples right here in this forum of what CAN be done in 3D with AutoCAD. Not knowing what a program can do is not so good for someone who offers support.