I have a polygon layer with multiple polygon features drawn on it.
I need a tool that will draw a bounding box around each polygon feature individually. Right now everything I try in the tool box draws a single bounding box that encompasses all the polygon features. Is there such a tool?
In the Processing Toolbox (Processing Tab > Toolbox or Ctrl+Alt+T) you will find a tool called Bounding boxes. This will achieve what you want.
If your layer contains some multipart features you might want to run the Multipart to singleparts first (Depending on what output you want.)
Input > Output:
If you want to have a separate feature class for each bounding box, you need to use the iterate tool (click on the green arrow) to get a bounding box for each polygon.
Without using the iterator, you will get all bounding boxes in one fearture class:
But using the iterator (the green arrow) will produce a bounding box for each polygon individually as a new feature class:
There is a possibility using a "Virtual Layer" through Layer > Add Layer > Add/Edit Virtual Layer...
Let's assume there is a polygon layer called 'test' with its corresponding attribute tables, see image below.
With the following query, it is possible to get the bounding box for each feature in the source layer.
SELECT id,
ST_Envelope(geometry) AS geom,
ST_AsText(ST_Envelope(geometry)) AS geom_text,
-- XMIN,YMIN,XMAX,YMAX
x_min(ST_Envelope(geometry)) || ',' ||
y_min(ST_Envelope(geometry)) || ',' ||
x_max(ST_Envelope(geometry)) || ',' ||
y_max(ST_Envelope(geometry)) AS bbox
FROM "test"
The output polygon layer (grey) with its attribute table will look like
Here is a solution using python
def boundingbox(shp_dir, out_dir, obj_file, epsg='4326'):
save_name = 0
obj = glob.glob(obj_file + '/*.shp')[0]
df = gpd.read_file(obj)
# iterrate through verticies to find min and max of y and x
for vertex in df.geometry:
x, y = vertex.exterior.coords.xy
xmin = min(x)
xmax = max(x)
ymin = min(y)
ymax = max(y)
# Create rectangle points
upper_left = (xmin, ymax)
upper_right = (xmax, ymax)
lower_left = (xmin, ymin)
lower_right = (xmax, ymin)
# save shapefile containing one bounding box shape
w = shapefile.Writer(shp_dir + str(save_name) + '.shp')
w.field("name", "C") # pyshp needs at least one field
w.poly([[lower_left, lower_right, upper_right, upper_left]]) # generate bbox polygon
w.record('bbox')
w.close()
# generate .PRJ file
crs_wkt = 'epsg: ' + epsg
prj = open(shp_dir + str(save_name) + '.prj', "w")
prj.write(crs_wkt)
prj.close()
save_name = save_name + 1
shapefiles = glob.glob(shp_dir + '/' + '/*.shp')
gdf = pandas.concat([
gpd.read_file(shp)
for shp in shapefiles
]).pipe(gpd.GeoDataFrame)
gdf.crs = ('epsg:4326')
gdf.to_file(out_dir + '/' + 'merged.shp')
Here is a basic PyQGIS solution without external libraries:
layer = iface.activeLayer()
newlayer = QgsVectorLayer("Polygon?crs={}&index=yes".format(layer.crs().authid()), "BoundingBoxes", "memory")
with edit(newlayer):
newlayer.dataProvider().addAttributes(layer.fields()) # copy the fields to the outputlayer
newlayer.updateFields() # save the changes
for feat in layer.getFeatures(): # iterate over inputlayer
bbox = feat.geometry().boundingBox() # get the Boundingbox as QgsRectangle
bbox_geom = QgsGeometry.fromRect(bbox) # Turn the QgsRectangle into QgsGeometry
outfeat = QgsFeature() # Create a new feature
outfeat.setAttributes(feat.attributes()) # copy the attributes to the outputlayer
outfeat.setGeometry(bbox_geom) # set the geometry of the outputfeature to the bbox of the inputfeature
newlayer.dataProvider().addFeature(outfeat) # add the feature to the outputlayer
QgsProject.instance().addMapLayer(newlayer)
It copies the features from the inputlayer 1 to 1 with all attributes and uses the inputfeatures boundingbox as geometry.
To add a solution using QGIS expressions with Geometry generator or Geometry by expression (see here for differences) - use this expression:
bounds ($geometry)
Initial polygons in orange, boundin boxes created with geometry generator in blue:
