GIS text

gis.txt

Creating & editing a new vector layer
 
Code snippets follow along
 
vl = QgsVectorLayer("Point", "temp", "memory")
 
 
from qgis.PyQt.QtCore import QVariant
pr = vl.dataProvider()
pr.addAttributes([QgsField("name", QVariant.String),
                  QgsField("age",  QVariant.Int),
                  QgsField("size", QVariant.Double)])
vl.updateFields() 
 
 
f = QgsFeature()
f.setGeometry(QgsGeometry.fromPointXY(QgsPointXY(10,10)))
f.setAttributes(["Ada L.", 2, 0.3])
pr.addFeature(f)
vl.updateExtents() 
QgsProject.instance().addMapLayer(vl)
 
 
print("No. fields:", len(pr.fields()))
print("No. features:", pr.featureCount())
e = vl.extent()
print("Extent:", e.xMinimum(), e.yMinimum(), e.xMaximum(), e.yMaximum())
 
for f in vl.getFeatures():
    print("Feature:", f.id(), f.attributes(), f.geometry().asPoint())
 
 
vl.startEditing()
 
my_field_name = 'new field'
vl.addAttribute(QgsField(my_field_name, QVariant.String))
vl.updateFields()
 
for f in vl.getFeatures():
    print("Feature:", f.id(), f.attributes(), f.geometry().asPoint())
 
 
my_field_value = 'Hello world!'
for f in vl.getFeatures():
    f[my_field_name] = my_field_value
    vl.updateFeature(f)
 
vl.commitChanges()
 
for f in vl.getFeatures():
    print("Feature:", f.id(), f.attributes(), f.geometry().asPoint())
 
 
iface.vectorLayerTools().stopEditing(vl) 
 
 
my_field_name = 'new field'
my_field_value = 'Hello world!'
 
with edit(vl):
    vl.addAttribute(QgsField(my_field_name, QVariant.String))
    vl.updateFields()
    for f in vl.getFeatures():
        f[my_field_name] = my_field_value
        vl.updateFeature(f)
 
 
uri = "/Users/johnssc5/Documents/natural_earth_vector.gpkg/packages/natural_earth_vector.gpkg|layername=ne_110m_admin_0_tiny_countries"

result = processing.run("native:buffer", 
    {'INPUT':uri,'DISTANCE':10,'SEGMENTS':5,'END_CAP_STYLE':0,'JOIN_STYLE':0,'MITER_LIMIT':2,
    'DISSOLVE':False,'OUTPUT':'memory:'})

result = processing.run("native:buffer", 
    {'INPUT':uri,'DISTANCE':10,'SEGMENTS':5,'END_CAP_STYLE':0,'JOIN_STYLE':0,'MITER_LIMIT':2,
    'DISSOLVE':False,'OUTPUT':'memory:'})
 
QgsProject.instance().addMapLayer(result['OUTPUT'])


Chaining Processing tools
my_gpkg = 'E:/Geodata/NaturalEarth/natural_earth_vector.gpkg'
rivers = '{}|layername=ne_110m_rivers_lake_centerlines'.format(my_gpkg)
places = '{}|layername=ne_110m_populated_places'.format(my_gpkg)
 
expression = "name = 'Donau'"
danube = processing.run("native:extractbyexpression", 
    {'INPUT':rivers,'EXPRESSION':expression,'OUTPUT':'memory:'}
    )['OUTPUT']
 
buffer_distance = 0.1 #degrees 
 
buffered_danube = processing.run("native:buffer", 
    {'INPUT':danube,'DISTANCE':buffer_distance,'SEGMENTS':5,'END_CAP_STYLE':0,
    'JOIN_STYLE':0,'MITER_LIMIT':2,'DISSOLVE':False,'OUTPUT':'memory:'}
    )['OUTPUT']
 
places_along_danube = processing.run("native:extractbylocation", 
    {'INPUT':places,'PREDICATE':[0],'INTERSECT':buffered_danube,'OUTPUT':'memory:'}
    )['OUTPUT']
 
QgsProject.instance().addMapLayer(places_along_danube)
 
for feature in places_along_danube.getFeatures():
    print(feature["name"])