Creating polygon shapefile from bounding box in ogr from osgeo?

Question

I'm trying to create a polygon shapefile from a bounding box in ogr but it creates an empty shapefile. Here's the code:

from osgeo import ogr

infc = r"C:\Temp\infc.shp"
layer_name = 'outfc_bbx'

driver = ogr.GetDriverByName("ESRI Shapefile")
vector = driver.Open(infc)
in_lyr = vector.GetLayer()

driver = ogr.GetDriverByName('ESRI Shapefile') # will select the driver foir our shp-file creation.
shapeData = driver.CreateDataSource(r"C:\Temp") #so there we will store our data
out_lyr = shapeData.CreateLayer(layer_name, in_lyr.GetSpatialRef(), ogr.wkbPolygon) #this will create a corresponding layer for our data with given spatial information.
out_lyr.CreateFields(in_lyr.schema)
out_defn = out_lyr.GetLayerDefn()
out_feat = ogr.Feature(out_defn)

feature = in_lyr.GetFeature(0)
geom = feature.GetGeometryRef()
geom.GetEnvelope()
(minX, maxX, minY, maxY) = geom.GetEnvelope()
ring = ogr.Geometry(ogr.wkbLinearRing)
ring.AddPoint(minX, minY)
ring.AddPoint(maxX, minY)
ring.AddPoint(maxX, maxY)
ring.AddPoint(minX, maxY)
ring.AddPoint(minX, minY)
polygon_env = ogr.Geometry(ogr.wkbPolygon)
#poly = polygon_env.GetGeometryRef(0)
out_feat.SetGeometry(polygon_env)
out_lyr.CreateFeature(out_feat)

Answer 1

You are creating a new feature:

feature = in_lyr.GetFeature(0)
geom = feature.GetGeometryRef()
geom.GetEnvelope()
(minX, maxX, minY, maxY) = geom.GetEnvelope()

Then you create the ring for the polygon:

ring = ogr.Geometry(ogr.wkbLinearRing)
ring.AddPoint(minX, minY)
ring.AddPoint(maxX, minY)
ring.AddPoint(maxX, maxY)
ring.AddPoint(minX, maxY)
ring.AddPoint(minX, minY)

Now you create your polygon for the bounding box:

polygon_env = ogr.Geometry(ogr.wkbPolygon)
#poly = polygon_env.GetGeometryRef(0)

And here you add the bounding box polygon to the layer:

out_feat.SetGeometry(polygon_env)
out_lyr.CreateFeature(out_feat)

But you haven't actually connected the ring to the bounding box polygon. The bounding box polygon is empty, because you still need to add the ring to the polygon:

...
polygon_env = ogr.Geometry(ogr.wkbPolygon)

# This is the missing line:
polygon_env.AddGeometry(ring)

# Add the polygon to the new feature.
out_feat.SetGeometry(polygon_env)
...