For a formula that you can implement, see this page for an explanation and scroll down the bottom for various implemenations 3857 to/from 4326
Python Implementation provided:
def MetersToLatLon( mx, my ):
"Converts XY point from Spherical Mercator EPSG:900913 to lat/lon in WGS84 Datum"
lon = (mx / originShift) * 180.0
lat = (my / originShift) ...
I do not see that as one of the options for the Search widget. If it truly is not an option in the OOTB widget, you can always write your own widget - use an HTML text box, maybe an autocomplete library like jQuery UI Autocomplete, and wire it up to use the Locator task, and after you get the results do your additional geometry filter using the Geometry ...
You may have more luck with the Photon Geocoder described at https://wiki.openstreetmap.org/wiki/Photon . You can contact Komoot for the usage policy on their public instance.
Photon does provide a 53GB compressed search index of the whole world, see github for installation details. They don't mention uncompressed size of the index, though.
YAddress (made by the company I work for) does address validation and correction in one pass with geocoding. For every address, you get an error code that tells you if the address was correct or not, and if not, what the problem was.
In the process of correcting the address, all typos, misspellings and other human issues are taken care of. It also resolves ...
YAddress (made by the company I work for) can geocode batches of address with city-state lines only, without the street lines. It is free for small batches and paid for large ones.
For each city you get coordinates of the city centroid, with is an imaginary center of mass of the city area.
I have had the exact same problem for months and did the same things that you did. However, today, I discovered that there is a new version of MMQGIS out. I just updated the plugin and have been able to successfully geocode the addresses I have.
Here's what ended up working for me. Not geocoding, but using a gazetteer:
Download the USGS U.S. Board on Geographic Names GNIS Data Topical Gazetteer "Populated Places" from: https://www.usgs.gov/core-science-systems/ngp/board-on-geographic-names/download-gnis-data
Save the gazetter text file as an XLSX file, use Text to Columns to separate into columns, ...
I was having the same issue, what seemed to work is to create an empty directory, and save the .shp file in that, e.g.:
Also, make sure the Not Found Output List is saved to a different directory.
You can install the MMQGIS plugin from Plugins ~> Manage and Install Plugins menu.
Search for mmqgis plugin, select it and click on Install plugin.
If you can't find it, check that you have the repository well configured in the Plugins | Settings tab.
If you see a No Python support detected message there, that is another problem and the following ...