[Qgis-user] Did scale change outputting to PDF?
Andreas Neumann
a.neumann at carto.net
Wed May 26 23:43:29 PDT 2021
Hi again John,
Another thing: what projection (CRS) did you use? Not all CRS are
suitable for printing to scale - esp. the Web Mercator projections are
often not suitable.
Greetings,
ANdreas
On 2021-05-27 08:20, Andreas Neumann wrote:
> Hi John,
>
> A very common error when printing PDF maps (regardless of the software
> that generated the PDF), is that the print shop scales it down to fit
> the "printable" area. Then you end up at somewhere around 95% (plus /
> minus) a bit
>
> The PDF viewers (at least the Acrobat one) has a setting to print at
> 100% (but this is not the default) - it has to be done consciously.
> However, this normally scales uniformly, not separately for width and
> height.
>
> On the topic of "base maps":
>
> Can you explain what source/mechanism for "base maps" you used? Are you
> refering to "tiled" maps, perhaps consumed through the OpenLayers
> plugin? This plugin is a known to be a source of error for
> misalignments and the plugin should be avoided. Even if you didn't use
> this plugin, I have to say that tiled base maps (e.g. consumed by the
> quick map services plugin or otherwise) are usually not suited for
> printing as their resolution is optimized for screen viewing. Printing
> these tiles would result in disappointing quality.
>
> Greetings,
>
> Andreas
>
> On 2021-05-27 07:15, John Antkowiak wrote:
>
>> 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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