WP plugin development - saving form data to database

I have a WP website that allows users to create posts from the front end using a form that I have already created. When users submit the form I need to trigger some functions that read some form data and process it in order to complete other post fields.

I'm using a plugin called Toolset Forms to produce my forms. It has a hook that we can hook the function into that's fired when the data from the form is being saved - cred_save_data
https://toolset.com/documentation/programmer-reference/cred-api/#cred_before_save_data

Part One:
Users are recording locations using a Google Map location, which uses latitude/longitude coordinates. When the form is submitted, I want the system to read some GIS shape files that we have. This will match the location to some data in the shape file that will then add additional data to other custom fields in the post.

Part Two:
Similarly, when the form is submitted, I want to convert the latitude/longitude coordinates to National Grid References, as well as Eastings and Northings. I have some formulae that should help with that. The converted coordinates would be saved in additional custom fields.