How to implement keyword and location search with MongoDB?

I am trying to implement a web/smart phone app that allow users to search for places based on keywords and location and here is the requirement:

• Users shall be able to search by typing in keywords and location; Locations can be zip code, city/state or current location from the mobile app (lat and long)
• We would like to be able to customize relevance score; We need to be able to define our own relevance algorithm based on keyword matching, location matching and some other parameters.

We use ASP.NET MVC as our web development framework and MongoDB as a data store. We also maintain a list of all zipcode and city/state as well as their centroid (lat/long) in our database. Our thought is override the scoring that the full-text system provide (like Lucene scoring) with our own algorithm. I am trying to find the best solution to address this. I am wondering whether should we use MongoDB full-text search or try to use Lucene .NET or perhaps Solr? Any help/pointer/comment is always apprecated!

Copyright Notice：Content Author:「Matt W」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/6735596/how-to-implement-keyword-and-location-search-with-mongodb