[Qgis-user] Fw: Did scale change outputting to PDF?

Thu May 27 01:42:49 PDT 2021

Hi John,

Another source of error is that you accidentally change the map scale 
during exporting the PDF map sheets in QGIS.

Did you generate the PDF in the main QGIS window or in the "Menu Project 
--> Import/Export --> Export map to PDF" or by making a print layout in 
the separate print layout window and then exporting from there?

I strongly recommend the latter approach.

Also, when you generate a series of PDFs with the same scale and 
different extend, you should preferably use the Atlas print 
functionality - maybe you did that anyway.

Not knowing more about the process, I can see several stages in the 
process where the map scale may accidentally change.

Also - you may already know this - but to state the obvious: the map 
scale in the main QGIS windows is not tightly linked to the map scale of 
the print layout window. They are independent.

Hope this all helps a bit and makes sense?

Andreas

On 2021-05-27 10:15, Andreas Neumann wrote:

> Hi John,
> 
> No - the PDF export does not distort the scale. But the printing of the 
> PDF file might.
> 
> It is absolutely important that - when printing the PDF - the setting 
> "Actual size" or "Custom Scale at 100%" is used. All other options will 
> change the scale.
> 
> As far as I know, the default option when printing is "Fit", which will 
> often shrink the content by some percentage - because some often 
> "invisible" or white background might be present in the file that 
> extends right to the edge of the page format. Acrobat then thinks that 
> the content goes beyond the "printable area" of the printer and will 
> scale down the whole file.
> 
> Hope that clarifies this potential pit-fall when printing PDF files. It 
> might well be a different issue than the one I describe, but this is a 
> very common source of error that I know.
> 
> Andreas
> 
> On 2021-05-27 10:02, John Antkowiak wrote:
> 
> Hi, Jochen. Your suggestion sounds do-able; I'll play around with it 
> and see if I can sort it out. I've got some digital calipers around 
> here somewhere :)
> 
> What I'm hearing is that the process of converting both the base map 
> (and yes, I did create it in QGIS) and the parcel maps into PDF will 
> distort the scale. (And that a print shop might compound the problem by 
> manually fitting the source file to the printable area. Yes?) A 
> question then is why didn't the PDF conversion distort them all the 
> same way, to the same degree? The base maps are done now and I couldn't 
> afford to do them again no matter what, so they are what they are. 
> Going forward, is there an export option in Print Layout that will not 
> distort the scale of the parcel maps?
> 
> I am so relieved that someone has an explanation for this!
> 
> - John A.
> 
> ----- Forwarded Message -----
> From: j.huber at post-ist-da.de <j.huber at post-ist-da.de>
> To: "qgis-user at lists.osgeo.org" <qgis-user at lists.osgeo.org>
> Sent: Thursday, May 27, 2021, 03:33:12 AM EDT
> Subject: Re: [Qgis-user] Did scale change outputting to PDF?
> 
> Hi John,
> 
> as I understand it, you created the base map in QGIS. If you use the 
> measure tool in QGIS to get the distance between two distinct features 
> in the map (e.g. road intersections) and then measure the same distance 
> on the printed base map with a ruler, it should be possible to 
> calculate the scale. Maybe use two distances, one aligned more or less 
> horizontally and one vertically, to check if the scaling is 
> proportional.
> 
> As Andreas pointed out, it is probably a problem with the settings when 
> the PDF was printed. In my experience it is a good idea to go to print 
> shops usually working for architects and engineers since they are 
> familiar with the importance of scaling (for advertising etc. it is 
> more important that the whole content is printed, so that scaling might 
> be used to fit the output to the printable area without potential 
> cropping).
> You can print directly to a plotter in QGIS if you have access to the 
> device, avoiding the PDF detour.
> 
> EPSG 2264 should be fine. Units should be US feet.
> 
> Regards
> Jochen
> 
> Am 27.05.21 um 07:15 schrieb John Antkowiak:
> 
> Hi. This plan was too simple to fail - but it failed. The charity whose 
> project this is needed a large (that is... massive) paper wall map on 
> which to plot and rethink its delivery driver assignments. Both drivers 
> and delivery addresses are subject to change from week to week but it's 
> not a pizza delivery; this is a regular run to supply people in a bad 
> way. So the plan was to print the base map (roads and road names and 
> county boundaries only) and then print 8.5 x 11 address maps with 
> parcel data and orthos. That way, the base maps don't change but the 
> physical parcel layer is flexible. (On top of that is a third paper 
> layer indicating which drivers go where so someone can stand back and 
> take in the whole picture graphically. Not a cutting-edge state of the 
> digital art solution, but not everyone is cut out for that. It is what 
> it is.) In order for this to work, the parcel maps have to be the same 
> scale as the base map. Which they were... in QGIS.
> 
> We have to convert all the maps to PDF to print them, and we had to 
> send the base map PDFs to FedEx/Kinkos to print the 9 map grid panels 
> at 42" by 62" each.
> 
> When we got the big base maps up on the wall, we discovered the scale 
> did not match the 8.5" x 11" parcel maps output to PDF and printed from 
> home. It's not off by a lot, but it's enough to be painfully obvious 
> from a single standard size sheet of paper. I don't know how to reverse 
> engineer the big map scale precisely enough to enter a new scale number 
> in the QGIS Print Layout. I didn't foresee it because this never 
> would've been a conceivable scenario at the engineering firm where I 
> picked up my meager GIS skills. (ArcMap sent a map directly to the 
> plotter without interim steps.) There was no scale bar on the map. It 
> shouldn't have been needed for this.
> 
> Did something happen to the map scale when QGIS output the map to PDF? 
> Could the size of the image on the pdf page have been adjusted manually 
> or otherwise when being sent to a plotter with 42" paper? Could the 
> image have been distorted horizontally differently from vertically? For 
> the life of me, I cannot trial-and-error guess at a scale to enter. 
> I've gone through dozens of new 8.5" x 11" test maps trying to guess 
> the correct scale.
> 
> Any ideas?
> 
> Thank you all -
> 
> John A.
> 
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