In VectorTile.cpp the wrong latitudes are calculated.

[Serinox]

Currently Cairo Egypt (specifically tile 9613,9626,14) is being calculated at roughly latitude -30 in the example project. I think this is due to a difference between the mbtile specification and the slippy tile spec that the tiley2lat and lat2tiley are expecting.

The mbtile format uses the "Tile Map Service Specification" which has incompatible tile indexing with slippy map tiles. The latitude functions seem to work when modified to be as follows:

double tiley2lat(int y, int z) 
{
	double n = pow(2.0,z);
	int ymax  = 1 << z;
	y = ymax - y - 1;
	double latRad = atan(sinh(M_PI*(1-(2*y/n))));
	return 180.0 / M_PI * latRad;
}

int lat2tiley(double lat, int z)
{
	int y = (int)(floor((1.0 - log( tan(lat * M_PI/180.0) + 1.0 / cos(lat * M_PI/180.0)) / M_PI) / 2.0 * pow(2.0, z)));
	int ymax  = 1 << z;
	y = ymax - y - 1;
	return y;
}

these modifications were found here https://alastaira.wordpress.com/2011/07/06/converting-tms-tile-coordinates-to-googlebingosm-tile-coordinates/

With the above changes Cairo is back at roughly latitude 30 comfortably above the equator.

[TimSC]

There is something weird going on... in openmaptiles.org tiles, Cairo is in 14/9613/9626 but in mapbox.com, it is 14/9613/6757... I need to have a think.

Update: As far as I can tell, the origin of tiles for mbtiles format is in the bottom left or south west (from a TileMill generated PBF, following the Tile Map Service Specification). However, for tile URLs the origin is in the top left/north west (following the google tiles convention). More info on the OSM wiki. Looks like I am worrying over nothing!

[TimSC]

Fix committed to master. Thx @Serinox!