[REQ] Map distance measurement 'scales' !!

vanjast · 01-12-09, 03:41 PM

While on my never-ending nav mod endeavour... another 'flaw' in SH4.. the map distance indicators...
The distance indicated in the pic below is ...eerrr.. very wrong, according to all Nautical sources. The correct distances are indicated.

My question is !!

Does anybody know where to control this 'Distance calculation scale' for the map ?
That's if this exists of course, and is not hard coded.

Correcting this is essential for navigating by Dead Reckoning and/or Navigation Logs.. besides Celestial navigation.

Thanks for any help

Munchausen · 01-12-09, 07:13 PM

On the SH4 map, distance between longitude lines never changes. No convergence as you approach the poles. Ergo, I would assume that, even if you could correct the distance for one north-south latitude, it wouldn't be correct for any other.

skookum · 01-12-09, 11:10 PM

That's wierd. The map is a mercator projection, which means the latitude scale doesn't change between the equator and the pole. Only the longitude scale changes. Theoretically, a slight change of map scale should rectify the problem. No?

vanjast · 01-13-09, 03:37 AM

The SH4 map is a mercator 'equidistant' projection (the distortion of the land masses higher/lower up), where the distances make sense up to the 80 latitudes, but thereafter it's a bit of a wobbly. But as we never 'have' to go above such latitudes, we can get away with this.

I have tried this, cannot remember though but think the game does make the correct speed/distance adjustments when close to the poles.

I have played with the 'metres-per-pixel' on the map scales but this still has no effect on the indicated map tools distances - which is important for manual course plotting.

The Long/Lat grid on the map looks as if it's 'locked' into this distance calculation.
Just need to 'unlock it'

Fincuan · 01-13-09, 08:57 AM

Distances measured are correct, but SH4 latitude degrees aren't 60nm. As you measured they're about 64.7 NM(119.8 km) throughout the map, which means we actually travel longer west-east distances ingame than in real life all the time. The further away from equator we are, the bigger the difference.

vanjast · 01-13-09, 12:21 PM

'SH4 earth' looks to be slightly larger than Real Earth

.. and scaled to to SH4 earth the 'distances are correct'. Now the trick is to scale the map (and game) to Real Earth so that all the documentation makes sense.

Did a quick measurement on the SH4 map... Latitude does not effect the distances measured, as mentioned earlier the map projection scales are 'equi-distant.

I think UBI mentioned that the devs went to painstaking lengths to ensure accuracy... Maybe they didn't have the time, or the right information.

01-12-09, 03:41 PM	#1
vanjast Sea Lord Join Date: Jun 2006 Location: Somewhere else now Posts: 1,739 Downloads: 825 Uploads: 4	[REQ] Map distance measurement 'scales' !! While on my never-ending nav mod endeavour... another 'flaw' in SH4.. the map distance indicators... The distance indicated in the pic below is ...eerrr.. very wrong, according to all Nautical sources. The correct distances are indicated. My question is !! Does anybody know where to control this 'Distance calculation scale' for the map ? That's if this exists of course, and is not hard coded. Correcting this is essential for navigating by Dead Reckoning and/or Navigation Logs.. besides Celestial navigation. Thanks for any help Last edited by vanjast; 01-12-09 at 04:14 PM.

01-12-09, 11:10 PM	#3
skookum Weps Join Date: Apr 2007 Posts: 351 Downloads: 35 Uploads: 0	That's wierd. The map is a mercator projection, which means the latitude scale doesn't change between the equator and the pole. Only the longitude scale changes. Theoretically, a slight change of map scale should rectify the problem. No? __________________

01-12-09, 07:13 PM	#2
Munchausen Commodore Join Date: Jul 2002 Posts: 608 Downloads: 25 Uploads: 1	On the SH4 map, distance between longitude lines never changes. No convergence as you approach the poles. Ergo, I would assume that, even if you could correct the distance for one north-south latitude, it wouldn't be correct for any other.

01-13-09, 03:37 AM	#4
vanjast Sea Lord Join Date: Jun 2006 Location: Somewhere else now Posts: 1,739 Downloads: 825 Uploads: 4	The SH4 map is a mercator 'equidistant' projection (the distortion of the land masses higher/lower up), where the distances make sense up to the 80 latitudes, but thereafter it's a bit of a wobbly. But as we never 'have' to go above such latitudes, we can get away with this. I have tried this, cannot remember though but think the game does make the correct speed/distance adjustments when close to the poles. I have played with the 'metres-per-pixel' on the map scales but this still has no effect on the indicated map tools distances - which is important for manual course plotting. The Long/Lat grid on the map looks as if it's 'locked' into this distance calculation. Just need to 'unlock it'

01-13-09, 08:57 AM	#5
Fincuan Admiral Join Date: Aug 2007 Location: Suomi, sauna, puukko, perkele Posts: 2,346 Downloads: 39 Uploads: 0	Distances measured are correct, but SH4 latitude degrees aren't 60nm. As you measured they're about 64.7 NM(119.8 km) throughout the map, which means we actually travel longer west-east distances ingame than in real life all the time. The further away from equator we are, the bigger the difference.

01-13-09, 12:21 PM	#6
vanjast Sea Lord Join Date: Jun 2006 Location: Somewhere else now Posts: 1,739 Downloads: 825 Uploads: 4	'SH4 earth' looks to be slightly larger than Real Earth .. and scaled to to SH4 earth the 'distances are correct'. Now the trick is to scale the map (and game) to Real Earth so that all the documentation makes sense. Did a quick measurement on the SH4 map... Latitude does not effect the distances measured, as mentioned earlier the map projection scales are 'equi-distant. I think UBI mentioned that the devs went to painstaking lengths to ensure accuracy... Maybe they didn't have the time, or the right information.