Thanks for your explanation.
There is one thing I don't understand.
Originally Posted by GPS-Marco
Moreover: both merc and tmerc are conformal and then x and y scales are identical.
I believed this was true only locally. When going far away from Equator, the scale goes down, no ?
So a large circle (60 degrees wide, for example) should not appear as a circle ?
Or is there another projection used by OCPN ? (a 'world' projection with a scale based on Equator)
Sorry for all these questions ... I promise I won't do it again ..