Data defined Size legend is wrong when using separated symbols

[qgib]

Author Name: Harrissou Santanna (@DelazJ)
Original Redmine Issue: 19099
Affected QGIS version: 3.4.1
Redmine category:map_legend

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The data-defined size symbols feature has a set of unhandled issues i reported months ago (see "list":/projects/qgis/issues?utf8=%E2%9C%93&set_filter=1&f%5B%5D=status_id&op%5Bstatus_id%5D=o&f%5B%5D=description&op%5Bdescription%5D=%7E&v%5Bdescription%5D%5B%5D=size+legend&f%5B%5D=&c%5B%5D=tracker&c%5B%5D=status&c%5B%5D=priority&c%5B%5D=subject&c%5B%5D=assigned_to&c%5B%5D=updated_on&group_by=) but i think this one is a really broken feature that can lead to wrong information on maps.

Apply a scaled size to a point layer
At the bottom of the properties, choose to enable the data defined Size Legend
In the new dialog, choose "separated legend items", do the other settings and apply.
Most of the times, the symbols won't scale in the preview frame nor in the layers panel but the size displayed in the layers panel, hence in the layout legend, is really wrong. Really bigger than what's displayed in the map canvas.
If you switch to the "collapsed size symbols", you'll notice the difference of size and that sizes are coherent now.

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• Multivariate analisys.pdf (Martina Savarese)

[qgib]

Author Name: Jürgen Fischer (@jef-n)

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• description was changed from The data-defined size symbols feature has a set of unhandled issues i reported months ago (eg https://issues.qgis.org/projects/qgis/issues?utf8=%E2%9C%93&set_filter=1&f%5B%5D=status_id&op%5Bstatus_id%5D=o&f%5B%5D=description&op%5Bdescription%5D=%7E&v%5Bdescription%5D%5B%5D=size+legend&f%5B%5D=&c%5B%5D=tracker&c%5B%5D=status&c%5B%5D=priority&c%5B%5D=subject&c%5B%5D=assigned_to&c%5B%5D=updated_on&group_by=) but i think this one is a really broken feature that can lead to wrong information on maps.

Apply a scaled size to a point layer
At the bottom of the properties, choose to enable the data defined Size Legend
In the new dialog, choose "separated legend items", do the other settings and apply.
Most of the times, the symbols won't scale in the preview frame nor in the layers panel but the size displayed in the layers panel, hence in the layout legend, is really wrong. Really bigger than what's displayed in the map canvas.
If you switch to the "collapsed size symbols", you'll notice the difference of size and that sizes are coherent now. to The data-defined size symbols feature has a set of unhandled issues i reported months ago (see "list":/projects/qgis/issues?utf8=%E2%9C%93&set_filter=1&f%5B%5D=status_id&op%5Bstatus_id%5D=o&f%5B%5D=description&op%5Bdescription%5D=%7E&v%5Bdescription%5D%5B%5D=size+legend&f%5B%5D=&c%5B%5D=tracker&c%5B%5D=status&c%5B%5D=priority&c%5B%5D=subject&c%5B%5D=assigned_to&c%5B%5D=updated_on&group_by=) but i think this one is a really broken feature that can lead to wrong information on maps.

Apply a scaled size to a point layer
At the bottom of the properties, choose to enable the data defined Size Legend
In the new dialog, choose "separated legend items", do the other settings and apply.
Most of the times, the symbols won't scale in the preview frame nor in the layers panel but the size displayed in the layers panel, hence in the layout legend, is really wrong. Really bigger than what's displayed in the map canvas.
If you switch to the "collapsed size symbols", you'll notice the difference of size and that sizes are coherent now.

[qgib]

Author Name: Alexandre Neto (@SrNetoChan)

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I have also noticed this problem. From some testing, seems that the symbols size in the legend is using the actual values on the data, and not the scaled values provided by the expression, for example.

coalesce(scale_exp("capacity", 0, 2717, 1, 10, 0.57), 0).

[qgib]

Author Name: Giovanni Manghi (@gioman)

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• version was changed from 3.1(master) to 3.3(master)

[qgib]

Author Name: Alexandre Neto (@SrNetoChan)

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@gioman, can we consider this a regression. I mean, this used to work just fine before this several options to represent the legend were implemented.

[qgib]

Author Name: Giovanni Manghi (@gioman)

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• priority_id was changed from Normal to High
• regression was changed from 0 to 1

[qgib]

Author Name: Martina Savarese (Martina Savarese)

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Think some of the other issues Harrissou linked are related to this problem. Attached file is a scheme of some test I have made, hope it can be some usefull

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• 13550 was configured as Multivariate analisys.pdf

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• Multivariate analisys.pdf (Martina Savarese)

[qgib]

Author Name: Florent Monkerhey (Florent Monkerhey)

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I confirm that this problem is still present on QGis 4.3.1

[qgib]

Author Name: Giovanni Manghi (@gioman)

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• version was changed from 3.3(master) to 3.4.1

[mrsatori]

Same problem with QGIS 3.8.0.