w/1.7.3, distinct() doesn't seem to work with an indexed geo field, though in it does in 1.6.4.

To replicate, run these 3 lines in mongo:

use test_distinct
db.commits.save(

{ "_id" : ObjectId("4ce63ec2f360622431000013"), "loc" : [ 55.59664, 13.00156 ], "author" : "FredrikL"}

)
db.runCommand(

{distinct: 'commits', key: 'loc'}

)

OK, we see one commit. But if the geo field is indexed, we get an exception.

> db.commits.ensureIndex(

{'loc': '2d'}

)
> db.commits.getIndexes()
[
{
"name" : "id",
"ns" : "test_distinct.commits",
"key" :

{ "_id" : 1 }

,
"v" : 0
},
{
"_id" : ObjectId("4ceadeb04ca1623d1ab8bcf3"),
"ns" : "test_distinct.commits",
"key" :

{ "loc" : "2d" }

,
"name" : "loc_"
}
]
> db.runCommand(

{distinct: 'commits', key: 'loc'}

)
{
"errmsg" : "exception: best guess plan requested, but scan and order required: query: {} order:

{ loc: \"2d\" }

choices:

{ $natural: 1 }

",
"code" : 13284,
"ok" : 0
}

In 1.6.4, this works (same inputs as above)

> db.runCommand(

{distinct: 'commits', key: 'loc'}

)

{ "values" : [ 13.00156, 55.59664 ], "ok" : 1 }