I have a map with a custom projection (for maps.yandex.ru tiles) and default projection (Google and OSM tiles). When I add KmlLayer to map in the default projection it seems ok:
But switching map to maps.yandex layer (in custom projection)...
and kml-objects are misplaced.
How do I tell KmlLayer about custom projection?
The way I understand it, any given object that has lat/lon (a,b) under a Mercator projection will have a different value than (a,b) under a custom projection. For example, if your custom projection was polar, the object would have distance from a fixed point and an angle from a fixed direction, and no lat/lon at all. So, the way to tell your KMLLayer about the custom projection would be to convert the coordinates of each object and rewrite the KML.
来源：https://stackoverflow.com/questions/10595931/how-to-tell-kmllayer-about-custom-map-projection