SUBSIM Radio Room Forums - View Single Post - SH3 Globe: Mercator or Gall Peters projection

Pisces · 11-01-11, 08:21 AM

I am positively sure it is neither of them. It's just a linear relationship between longitude and latitudes degrees on the real world vs. distances in kilometers against the SH(3) equator and GM-line. 1 degree equals 120 km. Measure it, you'll see.

This Gall-Peters projection (wiki) uses the sin-function for the vertical coordinate. The Mercator projection (wiki) uses a combination of natural logarithm and the tan or sin function. Both would make the relationship between RL latitude degrees and SH3 vertical kilometers non-linear. Those do not match up with the linear measurements I made. Besides, likely game-developers avoid these kind of functions if they can. As they are far to computationally intensive. An extra divide or multiply they don't have problems with these days.

Just looking at the shape of land features can be deceiving. I think screen resolution and aspect-ratio (wide-screen) issues might come into play. And to me neither look fitting the Sh3 map.

My proof:

In the game the north tip of the small island north of Iceland (Grimsey) is 7988.8 kilometers from the equator. It is in Google Earth at latitude 66d33m58.55s. Dividing 7988.8 (km) by 120 (km)=66.573333 in decimal notation. In dms-notation this is 66d34m24s The difference is about 850 meters in Google Earth. And 0.01% in relative terms.

Distances near the equator are just as linear, which I leave for you to test.

11-01-11, 08:21 AM	#3
Pisces Silent Hunter Join Date: Dec 2004 Location: AN9771 Posts: 4,904 Downloads: 304 Uploads: 0	I am positively sure it is neither of them. It's just a linear relationship between longitude and latitudes degrees on the real world vs. distances in kilometers against the SH(3) equator and GM-line. 1 degree equals 120 km. Measure it, you'll see. This Gall-Peters projection (wiki) uses the sin-function for the vertical coordinate. The Mercator projection (wiki) uses a combination of natural logarithm and the tan or sin function. Both would make the relationship between RL latitude degrees and SH3 vertical kilometers non-linear. Those do not match up with the linear measurements I made. Besides, likely game-developers avoid these kind of functions if they can. As they are far to computationally intensive. An extra divide or multiply they don't have problems with these days. Just looking at the shape of land features can be deceiving. I think screen resolution and aspect-ratio (wide-screen) issues might come into play. And to me neither look fitting the Sh3 map. My proof: In the game the north tip of the small island north of Iceland (Grimsey) is 7988.8 kilometers from the equator. It is in Google Earth at latitude 66d33m58.55s. Dividing 7988.8 (km) by 120 (km)=66.573333 in decimal notation. In dms-notation this is 66d34m24s The difference is about 850 meters in Google Earth. And 0.01% in relative terms. Distances near the equator are just as linear, which I leave for you to test. __________________ My site downloads: https://ricojansen.nl/downloads Last edited by Pisces; 11-01-11 at 08:33 AM.