Trying to understand CharacterPointerViewModel code

Hi,

I get your code from Github and I'm trying to understand the GW2 mapping system.

I already read those articles :
wiki.guildwars2.com/wiki/API:Maps
wiki.guildwars2.com/wiki/API:Tile_service

I'm looking at your code in CharacterPointerViewModel.RefreshCharacterLocation().
I understand the algorith used to get the character coordinates in GW2 grid ((0,0) to (49152, 49152)).
I also understand you need to get the lat, long through mercator projection.
What I don't understand is this part :
- charX - (cont.Width / 2)) / cont.Width * 360.0
- ((cont.Height / 2) - charY) / cont.Height * 360.0
What is the purpose of this transformation ?

I launched too the application and saw that the tiles are not ok with the character location.
Do you know why it worked and stop working ?

I know it'll take you a lot of time to answer all those questions but I'll be really happy to understand you code .

Hope to have the answers soon !
Bye