[GIS] Converting JSON to GeoJSON MultiPoint using `ogr.CreateGeometryFromJSON`

geojsonjsonogrosgeopython

I am trying to convert a JSON array to a geom in Python, by first converting it to a GeoJSON.

I have point coordinates in a JSON array,

[{'lat':100.0, 'lng':0.0},{'lat':101.0, 'lng':1.0'}]

that I want to convert to GeoJSON to then use as a geom in Python.

I convert the JSON array using a Python function,

def json2geojson(items):
    import json
    return json.dumps({
            "type": "MultiPoint", "coordinates":[ [ feature['lng'], feature['lat']]
                      for feature in json.loads(items)
            ]})

my_geojson = json2geojson(my_json)

which gives me this:

{ "type": "MultiPoint",
    "coordinates": [ [100.0, 0.0], [101.0, 1.0] ]
    }

Then I try to convert a geometry from the GeoJSON,

from osgeo import ogr

geom = ogr.CreateGeometryFromJson(my_geojson)

which at first glance appears to work

<osgeo.ogr.Geometry; proxy of <Swig Object of type 'OGRGeometryShadow *' at 0x113ea9ea0> >

however something clearly goes wrong

print "%d,%d" % (geom.GetX(), geom.GetY())
0,0
print "Geometry has %i points" % (geom.GetPointCount())
Geometry has 0 points

Does anyone know why this is not working or the best way to do this type of conversion?

Edit:

Code works for a single point:

from osgeo import ogr

geojson = """{"type":"Point","coordinates":[108420.33,753808.59]}"""
point = ogr.CreateGeometryFromJson(geojson)
print "%d,%d" % (point.GetX(), point.GetY())

From http://pcjericks.github.io/py-gdalogr-cookbook/geometry.html#create-geometry-from-geojson

Best Answer

A MultiPoint, by definition, comprises several points, so 

geom = '{"type": "MultiPoint", "coordinates": [[100.0, 0.0], [101.0, 1.0]]}'
geom = ogr.CreateGeometryFromJson(geom)
# iterate through the points
for i in range(0, geom.GetGeometryCount()):
   g = geom.GetGeometryRef(i)
   print "%d,%d" % (g.GetX(), g.GetY()) 
100,0
101,1

as explained in Iterate over Geometries in a Geometry

But it is easier with Shapely or PyGeoIf ("shapely ultralight"), most appropriate to address these issues:

from shapely.geometry import shape
geom = '{"type": "MultiPoint", "coordinates": [[100.0, 0.0], [101.0, 1.0]]}'
Multipt = shape(json.loads(geom))
print Multipt
MULTIPOINT (100 0, 101 1)
Multipt.type
'MultiPoint'
len(Multipt)
2 # 2 points
for point in Multipt:
    print point, point.x, point.y
POINT (100 0) 100.0 0.0
POINT (101 1) 101.0 1.0
from shapely.geometry import mapping
print mapping(Multipt)
{'type': 'MultiPoint', 'coordinates': ((100.0, 0.0), (101.0, 1.0))}

Or:

from pygeoif import geometry
Multipt = geometry.as_shape(json.loads(geom))
print multipt
MULTIPOINT(100.0 0.0, 101.0 1.0)
for point in multipt.geoms:
    print point, point.x, point.y 
POINT (100.0 0.0) 100.0 0.0
POINT (101.0 1.0) 101.0 1.0
print multipt.__geo_interface__
{'type': 'MultiPoint', 'coordinates': ((100.0, 0.0), (101.0, 1.0))}
Related Question