QGIS – Updating Symbol Size Units from mm to Map Units in Rule-Based Symbology

map-unitqgisrule-basedstylesymbology

I have a quite complex rule-based symbology that is currently using millimetres as size units.

All third levels look the same, they just have different parents.

Is there a way to change symbol size units from millimetres to map units for every rule entry so I don't have to click each entry and switch (which would be a pain in the * for a few dozen entries)?

When I have a categorized approach, I have the general symbology, that I can easily change and then applies to all categories, but how do I achieve that with a rule-based symbology?

The same goes for other aspects, like symbol size. Can I change that size for all symbols at once? e. g. from 15 mu to 18 mu.

Best Answer

Use the following script in QGIS Code Editor. It also works on nested rules. Select the layer before running the script.

layer = iface.activeLayer()
renderer = layer.renderer().clone()

def set_output_unit(rules):
    for rule in rules.children():
        rule.symbol().setOutputUnit(1) # 1: MapUnits    
        if rule.children():
            set_output_unit(rule)

rules = renderer.rootRule()
set_output_unit(rules)

layer.setRenderer(renderer)
layer.triggerRepaint()

Related Solutions

[GIS] Changing symbol size using the “Size assistant” in QGIS

In your case you would to represent size of the proportionality with a manual scale... It's not possible by this way as it show here

What you have to do is to define your mathematic function with scale_exp as the size assistant method:

Ex.

coalesce(scale_exp(Number, 1, 11000, 1, 10, 0.3),0)  

Coalesce replace the first value not null by 0.
First param: your Var
2: min value
3:max value
4:min size result
5:max size result
6: exponent param (the most important to you, try 0.3 and see).

QGIS – Update Rule-Based Symbology

Based on multiple posts like here and here, here's a way to automate rule-based symbology creation, making sure it handes all unique values from two property fields from a given Vector layer (Date and Origin in your case).

This works from the Python console on the active layer:

It creates an empty Rule based renderer.
Selects all Origins as possible categories in a CategoryRenderer
Goes through all available Dates, adds a rule for data matching a given date and refines the rule with the above mentioned categories

I tested this code (with other field names) and it works. Some extra python code might be needed if your dates are not already in a YYYY-MM format. Also, for each date, all categories will be listed not only the ones that belond to that date range. This can be improved as well by reworking the script

from random import randrange
layer = iface.activeLayer()

symbol = QgsSymbol.defaultSymbol(layer.geometryType())
rb_renderer = QgsRuleBasedRenderer(symbol)
root_rule = rb_renderer.rootRule()

rule = root_rule.children()[0].clone()


dateindex = layer.dataProvider().fieldNameIndex("date_field")
unique_values_date = layer.uniqueValues(dateindex)


originindex = layer.dataProvider().fieldNameIndex("origin")
unique_values_origin = layer.uniqueValues(originindex)

categories = []
for unique_value in unique_values_origin:
    # initialize the default symbol for this geometry type
    symbol = QgsSymbol.defaultSymbol(layer.geometryType())

    # configure a symbol layer
    layer_style = {}
    layer_style['color'] = '%d, %d, %d' % (randrange(0, 256), randrange(0, 256), randrange(0, 256))
    layer_style['outline'] = '#000000'
    symbol_layer = QgsSimpleFillSymbolLayer.create(layer_style)

    # replace default symbol layer with the configured one
    if symbol_layer is not None:
        symbol.changeSymbolLayer(0, symbol_layer)

    # create renderer object
    category = QgsRendererCategory(unique_value, symbol, str(unique_value))
    # entry for the list of category items
    categories.append(category)

# create renderer object
renderercat = QgsCategorizedSymbolRenderer('origin', categories)
print(renderercat)
dates = []
for unique_date in unique_values_date:
    rule = root_rule.children()[0].clone()
    rule.setLabel(str(unique_date))
    rule.setFilterExpression(f""""date_field"='{unique_date}'""")
    QgsRuleBasedRenderer.refineRuleCategories(rule,renderercat)
    root_rule.appendChild(rule)

print(root_rule)
#QgsRuleBasedRenderer.refineRuleCategories(root_rule,renderercat)
print(rb_renderer)
# assign the created renderer to the layer
if rb_renderer is not None:
    layer.setRenderer(rb_renderer)

layer.triggerRepaint()

With this sample data:

here's what you get after running the script:

Best Answer

Related Solutions

[GIS] Changing symbol size using the “Size assistant” in QGIS

QGIS – Update Rule-Based Symbology

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