How to develop a Webform field (text/hidden) that is updated via Google Maps interaction?


I would like to have my users to submit locations for me.
To do this I need a Webform with a field that is updated with interaction on on a map.

The problem is that I cannot figure how the data flows with Webform.
I already have working UI but I cannot save the data or show user defined markers between steps/pages like other fields before they are submitted.
In other words I can’t find those marker coordinates (json)from any of the altering function or other hooks.

How could I create a hidden field which has a separate UI for manipulating field’s value? Where should I be looking for data of marker data which isn’t submitted yet? How could I set it as marker data for the google map to show them?

From form hook I can find them:
$form_state[‘values’][‘submitted’][85][‘latlons’] but how could I get this data for the Webform hooks to be able to show it again on the page?
If I go back to map page/step all the values a reset? How can I get it to preserve them just like any other Webform field’s value?

Drupal version: