Adding MapProvider for small custom map

[TimThaler]

Hello and thanks a loot for this awesome software. I really enjoy using it.
Now i want to add my own custom map. This map uses the mercator projection but shows only a fraction of the world. (Like the provided Latvian and Lithuanian maps).
I struggle a lot to put this map into the right focus. Either the boundaries are not matching or the
tiles get not computed correctly.
Could someone help me with the setup of the following properties:

• orignX/orignY -> I do not know how to calculate these two values.
• I know the tile-resolution pre tile pre zoom level on the map (e.g. Zoom:0 resolution: 500km....)
  but how can i calculate the values of the function public static double GetTileMatrixResolution(int zoom)

Thankful for any advise (: