Hi Rebin,
Currently the aggregation framework is limited to use one special index as the first pipeline stage. Since full-text index and geospatial index classify as special indexes, presently they cannot be used together in a single aggregation query. See Queries cannot use both text and Geospatial Indexes for more information.
Could you elaborate on what you are trying to achieve? It will be helpful if you can post information such as:
Regards,
John Murphy