Creating rectangles from CSV coordinates via Python console in QGIS

Question

As of v3.10, there is an asPolygon method for qgis.core.QgsRectangle.

This runs:

QgsRectangle(1804512.8556, 5453390.58088, 1813512.8556, 5461390.58088).asPolygon()

However, no vector data (i.e. an actual rectangle) appears on-screen in the View.

Maybe all I've done is transpose the inputs and haven't actually created a feature, yes?

What do I need to add/specify to write features to either a temp or shp file? (my end goal is to iterate through records in the csv to create multiple rectangles in a single shp)

Answer 1

You can use the following structure. For other rectangles, add the highlighted lines (between ###) to a for loop.

layer = QgsVectorLayer("Polygon?crs=EPSG:2193", "Polygons", "memory")
QgsProject.instance().addMapLayer(layer)

#### Coordinates coming from CSV ###
xMin = 1804512.8556
yMin = 5453390.58088
xMax = 1813512.8556
yMax = 5461390.58088

rect = QgsRectangle(xMin, yMin, xMax, yMax)
polygon = QgsGeometry.fromRect(rect)

feature = QgsFeature()
feature.setGeometry(polygon)

layer.dataProvider().addFeatures([feature])
#####################################

Answer 2

Try the code snippet below. This will create a temporary layer, add a polygon feature with geometry created from a QgsRectangle and add the memory layer to your project.

You also need to know what CRS your csv coordinates are in and tell QGIS about it. I have commented the code to show you where to specify the CRS.

project = QgsProject().instance()

rect = QgsRectangle(1804512.8556, 5453390.58088, 1813512.8556, 5461390.58088)
geom = QgsGeometry().fromRect(rect)

ftr = QgsFeature()
ftr.setGeometry(geom)

#Define your Coordinate Reference System here
crs = 'crs=epsg:2193'

lyr = QgsVectorLayer('Polygon?{}'.format(crs), 'Test_polygon','memory')

with edit(lyr):
    lyr.addFeature(ftr)

project.addMapLayer(lyr)