Index for Geometry does not work as expected

Question

here is the output from my command-line. You can see that the first attempt to create an index fails. Then I just rename the loc-Field to coordinates and it works ??? Can somebody explain that to me. This seems like an strange behavior.

> db.nodes.find().limit(3)
{ "_id" : ObjectId("534d36b682beda5978db27c1"), "geo" : { "type" : "Point", "loc" : [ 9.7366511, 52.3711883 ] } }
{ "_id" : ObjectId("534d36b682beda5978db27c2"), "geo" : { "type" : "Point", "loc" : [ 9.7399576, 52.3691615 ] } }
{ "_id" : ObjectId("534d36b682beda5978db27c3"), "geo" : { "type" : "Point", "loc" : [ 9.7346094, 52.371738 ] } }
> db.nodes.ensureIndex({"geo":"2dsphere"})
{
        "createdCollectionAutomatically" : false,
        "numIndexesBefore" : 1,
        "ok" : 0,
        "errmsg" : "Can't extract geo keys from object, malformed geometry?: { _id: ObjectId('534d36b682beda5978db27c1'), geo: { type: \"Point\", loc: [ 9.7366511, 52.3711883 ] } }",
        "code" : 16755
}
> db.nodes.find().limit(3)
{ "_id" : ObjectId("534d36ea82be11ca6e9fb112"), "geo" : { "type" : "Point", "coordinates" : [ 9.7366511, 52.3711883 ] } }
{ "_id" : ObjectId("534d36ea82be11ca6e9fb113"), "geo" : { "type" : "Point", "coordinates" : [ 9.7399576, 52.3691615 ] } }
{ "_id" : ObjectId("534d36ea82be11ca6e9fb114"), "geo" : { "type" : "Point", "coordinates" : [ 9.7346094, 52.371738 ] } }
> db.nodes.ensureIndex({"geo":"2dsphere"})
{
        "createdCollectionAutomatically" : false,
        "numIndexesBefore" : 1,
        "numIndexesAfter" : 2,
        "ok" : 1
}

Answer 1

It isn't clear why the second attempt fails silently, but the major problem here is that your json structure doesn't quite adhere to the GeoJSON specification. reference

A "Point" GeoJSON structure should have it's coordinates contained in a key called "coordinates"—not "loc".

Try creating the index with { "_id" : ObjectId("534d36b682beda5978db27c3"), "geo" : { "type" : "Point", "coordinates" : [ 9.7346094, 52.371738 ] } }

And remember that longitude is always first in the coordinates array! :]