Allow user to place the origin marker on map for proximity search

Problem/Motivation

The proximity filter in Views work really well, all three options are great:

• Geocode Origin (with Autocomplete option)
  Geocodes origin from free text input, with Autocomplete option.
• Manual Origin (Default)
  Allow the Manual input of Origin as couple of Latitude and Longitude in decimal degrees.
• Client Location Origin
  Gets the Client Location through the browser HTML5 Geolocation API.

However, sometimes it's necessary to be able to define the origin very precisely, to be able to filter correctly.

Steps to reproduce

Use the client location through HTML5 geolocation, and be off by a few kilometers. Want to define the origin with precision, but not able to except, by manually entering latitude and longitude.

This is too difficult for most ordinary users.

Proposed resolution

There could be different solutions to this, which ever is easiest ... as long as origin can be placed on the map with a mouse :)

• Support selecting origin on a map with the mouse under "Manual Origin (Default)" (the latitude longitude option)
• Add option to refine "Geocode Origin" or "Client Location Origin (HTML5)" after a search or automatic location
• Add a new fourth option "Add origin on map"

Remaining tasks

Decide how to support setting origin marker on a map with the mouse.

User interface changes

API changes

Data model changes