Thursday, November 10, 2022

Automate boring tasks in QGIS with PyQGIS

 In this post, I will use PyQGIS to automate some boring tasks I often encounter in QGIS. Hope you will find something useful to your workflow. Lets get started...

If you don't know what pyqgis is, then read this definition by hatarilabs.com: "PyQGIS is the Python environment inside QGIS with a set of QGIS libraries plus the Python tools with the potential of running other powerful libraries as Pandas, Numpy or Scikit-learn".

PyQGIS allows users to automate workflow and extend QGIS with the use of Python libraries and the documentation can be accessed here.

This means knowledge of python programming is required to understand some of the codes below.



  Task 1~ Count number of opened/loaded layers in the layer panel

I often find myself trying to count the layers in my QGIS project layer panel, so a simple pyqis script to automate the process will be ideal especially when there are many layers on the layer panel to count.

# This will return the all layers on the layer panel
all_layers = QgsProject.instance().mapLayers().values()
print('There are', len(all_layers), 'on the layer panel.')


  Task 2~ Count features in loaded vector layer

In this task, I want to get the number of features in each layer am working on. This is similar to 'Show Feature Count' function when you right-click on a vector layer.

# Get all layers into a list....
all_layers = list(QgsProject.instance().mapLayers().values())

# Get all displayed names of layer and corresponding number of features ...
ftCounts = [ (l.name(), l.featureCount()) for l in all_layers ]
print(ftCounts)


  Task 3~ Switch on/off all layers

To turn ON or OFF all layer can be frustrating when you got many layers to click through. So why not auto mate it in just a click.

# Get list of layers from the layer's panel...
qgis_prjt_lyrs = QgsProject.instance().layerTreeRoot().findLayers()

# Use index to Set layer on or off....
qgis_prjt_lyrs[20].setItemVisibilityChecked(True) # True=On, False=Off

# Do for all...
for l in qgis_prjt_lyrs:
    l.setItemVisibilityChecked(False)


  Task 4~ Identify layers that are on/off

Lets extend task3 above, so we know which layers are on (visible) and which layers are off (hidden).

# Get list of layers from the layer's panel...
qgis_prjt_lyrs = QgsProject.instance().layerTreeRoot().findLayers()

# Check if a layer is visible or not...
layer_visibility_check = [ (l.name(), l.isVisible()) for l in qgis_prjt_lyrs ]
print(layer_visibility_check)

visibility_ture = [ l.name() for l in qgis_prjt_lyrs if l.isVisible() == True ]
print('Number of visible layers:', len(visibility_ture))

visibility_false = [ l.name() for l in qgis_prjt_lyrs if l.isVisible() == False ]
print('Number of visible layers:', len(visibility_false))


  Task 5~ Read file path of layers

This is useful when you have many layers and don't know where they are located on your machine. You will also see interesting paths to other remote layer such as WMS, etc

# Returns path to every layer...
layer_paths = [layer.source() for layer in QgsProject.instance().mapLayers().values()]
print(layer_paths)


  Task 6~ Read layer type of layers

We can check the 'type' of a layer.

# Get dict of layers from the layer's panel...
layersDict = QgsProject.instance().mapLayers()


for (id, map) in layersDict.items():
    print(map.name(), '>>', map.type())


  Task 7~ Create multiple attribute fields/columns

Lets say we want to add multiple integer fields/columns to a vector layer. The code below will create attribute fields for year 2000 to 2023, that is twenty three (23) attribute columns/fields on the selected vector layer.

# Get Layer by name...
layer = QgsProject.instance().mapLayersByName("NIG LGA")[0]

# Define dataProvider for layer
layer_provider = layer.dataProvider()

# Add an Integer attribute field and update fields...
layer_provider.addAttributes([QgsField("2000", QVariant.Int)])
layer.updateFields()

# Add bulk attribute fields...
for x in range(2001, 2023):
    layer_provider.addAttributes([QgsField(str(x), QVariant.Int)])
    layer.updateFields()

print('Done...')


  Task 8~ Read/List all names of layers on layer panel

Here we just want to return the displayed names of layers.
# Get all layers into a list....
all_layers = list(QgsProject.instance().mapLayers().values())

# Get all displayed names of layer
all_layers_names = [ l.name() for l in all_layers ]
print(all_layers_names)


  Task 9~ Save attribute table to dataframe

# Save attribute table into Dataframe...

import pandas as pd

# Get Layer by name...
layer = QgsProject.instance().mapLayersByName("NIG LGA")[0]

# get attribute columns names
col_names = [ field.name() for field in layer.fields() ]

lga_list = []
state_list = []
apc_list = []
pdp_list = []
lp_list = []
nnpp_list = []
winner_list = []


for feature in layer.getFeatures():
    lga_list.append(feature['lga_name'])
    state_list.append(feature['state_name'])
    apc_list.append(feature['APC'])
    pdp_list.append(feature['PDP'])
    lp_list.append(feature['LP'])
    nnpp_list.append(feature['NNPP'])
    winner_list.append(feature['Winner'])

df = pd.DataFrame([state_list, lga_list, apc_list, pdp_list, lp_list, nnpp_list, winner_list]).T

df.to_csv(r'C:\Users\Yusuf_08039508010\Desktop\...\test.csv')

print('Done....')


  Task 10~ Select from multiple layers and attribute fields

Here we want to conduct multiple selection of given keywords from all listed layers and all attribute fields.
# Query to Select from all listed layers and all attribute fields
search_for = {'Bauchi', 'SSZ', 'Edo', 'Yobe'}

for lyr in QgsProject.instance().mapLayers().values():
    if isinstance(lyr, QgsVectorLayer):
        to_select = []
        # fieldlist = [f.name() for f in lyr.fields()]
        for f in lyr.getFeatures():
            # Check if any of the search keyword intersects to
            # feature's row attribute. If true, get the feature ID for selection...
            if len(search_for.intersection(f.attributes())) > 0:
                to_select.append(f.id())
        if len(to_select) > 0:
            lyr.select(to_select)




  Task 11~ Convert multiple GeoJSON files to shapefiles

import glob

input_files = glob.glob(r'C:\Users\Yusuf_08039508010\Desktop\Working_Files\GIS Data\US Zip Codes\*.json')
for f in input_files:
    out_filename = f.split('\\')[-1].split('.')[0]
    input_file = QgsVectorLayer(f, "polygon", "ogr")
    
    if input_file.isValid() == True:
        QgsVectorFileWriter.writeAsVectorFormat(input_file, rf"C:\Users\Yusuf_08039508010\Desktop\Working_Files\Fiverr\2021\05-May\Division_Region_Area Map\SHP\US ZipCode\{out_filename}.shp", "UTF-8", input_file.crs(), "ESRI Shapefile")
    else:
        print(f, 'is not a valid input file')
        
print('Done Processing..., ', f)



Thank you for reading.

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