Adding Coordinates Manually at Entry/Update Time

[felipel]

What is discussed in https://forums.osclass.org/development/how-to-manually-set-latitude-and-longitude-of-an-item/ is what I want to do. I have looked at both the OSM and Google maps plugins and understand what database fields are involved.
What I am not familiar with is how the GUI end works. If I can avoid spending a lot of time to understand more code that would be a big plus. So,

• First, has someone already done this. It seems like it would be needed and, beyond needing to understand the existing code, not very hard.
• If not, any pointers would be appreciated.

Thanks.