czm_webMercatorMaxLatitude
The maximum latitude, in radians, both North and South, supported by a Web Mercator (EPSG:3857) projection. Technically, the Mercator projection is defined for any latitude up to (but not including) 90 degrees, but it makes sense to cut it off sooner because it grows exponentially with increasing latitude. The logic behind this particular cutoff value, which is the one used by Google Maps, Bing Maps, and Esri, is that it makes the projection square. That is, the extent is equal in the X and Y directions. The constant value is computed as follows: czm_pi * 0.5 - (2.0 * atan(exp(-czm_pi)))