I am putting together some code to create tiles from various maps, for various planetary bodies, but I am not sure which value of planet radius I should be using, for indicating the metres/pixel during display?
- When I look at the Open Street Maps entry on 'zoom levels' a value of 6372.7982 km is given.
Looking at the 'Earth Fact sheet' I see:
- Equatorial radius (km): 6378.137
- Polar radius (km): 6356.752
- Volumetric mean radius (km): 6371.008
Wikipedia provides a value of 6371 km, which corresponds to the 'Volumetric mean radius' of the NASA fact sheet.
- Google appears to be using the value of 6378.13 km, basing on the circumference indicated in this other Stack Exchange answer.
Ideally I would like to use the data from the 'Planetary Factsheet' (for consistency across planetary bodies), so I am wondering whether I better off using the 'Equatorial radius' or the 'Volumetric mean radius' as reference value? BTW I should note that I will be using this along with metres per pixel equation, specified on the Open Street Map entry, on 'zoom levels':