[Qgis-user] QGIS Atlas gymnastics

[Alexandre Neto]

Ah! good to see that video put to good use :-)

Yes, Zoltan, all you ask seems possible to me. The secret is in the way you
prepare your coverage layer to iterate over the items. Check the video
comment as I forgot to explain one step in the video.

I also have this old blog post that covers dynamic size pages. The
expressions are a bit outdated. that is, there are now functions that make
the expressions easier:

https://gisunchained.wordpress.com/tag/atlas/

Alexandre Neto
QGIS Support
www.qcooperative.net

On Fri, Oct 15, 2021 at 9:53 AM Roland Spielhofer <rspiel at gmx.net> wrote:

> Hi Zoltan,
> I guess your first item is covered here:
> https://www.youtube.com/watch?v=NCsnTt6uxXo
>
> I call the video "Atlas on steroids" ;-)
>
> Regards,
> Roland
>
>
>
> *Gesendet:* Freitag, 15. Oktober 2021 um 10:39 Uhr
> *Von:* "Zoltan" <zoltans at geograph.co.za>
> *An:* "qgis-user" <qgis-user at lists.osgeo.org>
> *Betreff:* [Qgis-user] QGIS Atlas gymnastics
> Hi,
> I wonder if someone can confirm if below is possible or not, using the
> Atlas facilities  QGIS 3.20.3 in WIndows 10.
>
> Two issues, the second relying on the first.
> *#1 Variable size Map Item.*
> I would like to vary the size of the Map Item window, depending on the
> zoom window of the Atlas page.
> I can set the "Position and Size" using an Expression or an attribute
> Field, but this seems to be fixed rather than dynamic
> ie: Is it possible to have Expression and/or Field values dynamic per
> Atlas coverage page?
>
> *#2 Multiple Sub-maps per MapSheet.*
> Is it possible to have an Atlas page layout such that (say) in the top
> half of the page you have your zoomed map (as in #1 above) and in the
> bottom half of that sheet-page you place n-mapboxes  as insets predefined
> as n-AOI rectangles inside the zoom-window in the top of this MapPage?
>
> *A practical example/use would be:*
> Say you are doing an aerial analysis of a stretch of river and you have
> identified areas of interest by placing oriented rectangles around them.
> You now want to show an overview of segments of the river, and then a
> zoom-in to each identified AOI rectangle to show larger scale prints below
> this river segment.
>
> *Method could/would be to:*
>
> Using the width of your intended page size, calculate the length of river
> you can fit across 1 page of your Atlas. Let's assume 1Km
> Now a river meanders so you cannot run down the polyline depicting the
> river, you need to rotate and cut the river to the width of your atlas page.
> This means your atlas Map-Item width will be constant, but the height, due
> to curvatures in the river, will vary.
> Once you have your oriented MBRs calculated along the river, you can use
> these as your Atlas Coverage layer.
> To show this with optimal page-area usage, you would need the Atlas
> facility I describe in *#1 above*.
>
> Now, along the river you will have pre-placed your oriented AOI rectangles.
> These will be much smaller rectangles than the 1Km river-length Atlas
> Coverage rectangles.
> Now, for each AOI rectangle inside the current 1Km coverage rectangle, I
> want to show a larger scale image below the current coverage rectangle.
> If* #2 above* was possible and flexible, one could use the calculated
> (current) bottom left paper coord of the coverage rectangle to calculate
> the top-left position of the first AOI area.
> And so on across then down the remaining Atlas page for subsequent AOI
> boxes, which will likely be of varying size.
>
> I suppose this is rather like wanting an Atlas page-set within and Atlas
> page.
>
> Anyone achieved something like this?
> Does this sound useful?
>
> I guess, unless I've missed some facility in Atlas, I will be doing this
> by using the Atlas facility to spit out carefully named jpeg images, and
> then assembling the pages using Python and LibreOffice (or something).
>
> All thoughts/directions welcome.
>
> Kind regards,
> Zoltan
>
>
>
> --
>
> =============================================
> Zoltan Szecsei GPrGISc 0031
> Geograph (Pty) Ltd.
> GIS and Photogrammetric Services
>
> Cape Town, South Africa.
>
> Mobile: +27-83-6004028 (Signal, not WhatsApp)www.geograph.co.za
> =============================================
>
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