[Qgis-user] QGIS Atlas gymnastics

[Zoltan]

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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