I’m trying to get the altitudes at the start and end of runways, and if I check -for instance- MMGD on Isla Guadalupe, the runway object reports an altitude of 1950 feet, with a slope of 6.27 degrees (explicitly degrees according to the SDK docs, not percentages), and a runway length of 2540 feet. When I spawn a plane on that runway, the altitude at the two ends is 1950 on one end, and 1956 on the other. If I do the math, however, one end should be 1950 and the other should be (2540 * tan(rad(6.27))) feet higher, which would be an incredible 280 feet higher.
What am I missing with regards to runway slope?
(Or, is this one of those instances where the slope in degrees is actually degrees instead of radians? Because I’m converting from radians to get the slope value, since every single sim variable that’s in degrees is reported in radians…)
The SDK documentation, especially for the airport container objects, is notoriously sloppy with units. Runway lengths can be expressed in feet but are written to the .xml as meters. Degrees become tenths, magnetic courses become true course. It’s an good example of how little they knew about aviation and how poor the quality control it in the early days at Asobo. Too bad they don’t take the time to clean this slop up.
This isn’t even remotely Asobo’s fault, but Microsoft. Asobo didn’t invent SimConnect, they inherited it as part of the Microsoft Flight Simulator series. The only thing they could (and have) done is keep updating it in the same way it’s been updated for the last 2 decades or so.
Unfortunately the game does not always agree with the real world, so what matters is that SimConnect reports what the in-game runway length is, based on how someone implemented that runway, because that’s what the in-game plane is going to have to land on.
(for this particular “airport”, there looks to be around 3500’ of tarmac, but only 2500 of it has a center line, so giving it a length based on what’s actually flown on makes at least some sense)
Checking a few more airports, most notably Lukla, it appears that even though on the simvar side of the fence, degrees are encoded as rad, in the runway struct they are actual degrees (7.2 if used as is, over 400 if converted from rad, so that’s a pretty strong sign it can’t possibly be rad, and 7.2 is close enough to Lukla’s documented runway gradient to be the actual in-game value)
I agree the sim isn’t showing the airport correctly, but using the shorter length is obviously throwing the math way off.
One thing that stands out is when you do spawn on 04, you are already about 1/3 down the runway length.
This may be where the runway distance is calculated from, which is an incorrect start point.
It’s entirely the correct starting point: that’s the start of the center line. The aerial on google maps etc. clearly show the tarmac strip being longer than the actually usable part of the runway, so any “real” value that says the runway is longer than 2500 feet considers “all the tarmac” to be runway, rather than just the part that actually has runway markings.
(because… military? who knows)
And much like the runway length, the runway slope is based on the in-game data, so that’s fine. I only care about having the correct values for in-game flying, MSFS can be as wrong about them as it wants to be, as long as they interrelate correctly =)
(getting plenty of fun mismatches between in-game elevation and actual elevation based on ALOS’s 30m resolution world DEM as it is, so terrain follow is sometimes hilariously wrong. Would be nice if you could query the in-game elevation using SimConnect, but the only way to do that is to spawn a probe object and check it’s elevation, which is about the worst API if you want an elevation slice…)
Also, Little NavMap will read the game’s data files in order to populate its map. What it displays depends on one’s settings, but it can be configured to display what’s actually in the game.
Yes, thanks, I had posted the info so that the OP would consider that there seems to be an issue with the runway length in the sim.
The sim does show the scenery exactly the same as shown on any map app.
Both a real map pic and the sim show the dashed center line starting about a third of the distance down the runway.
The difference in length could probably be due to a start point placed at the end of the dashed center line, rather than at the end of the runway.
(For those that don’t know, start points can be placed anywhere)
I had a look in Google Earth, and it looks to me like the end of the runway 04 at MMGD that extends west of where the dotted lines start is dirt. East of there, it seems to be hard surface… Maybe concrete? The runway seems to have a hump in it. The ends of the hard surfaced portion seem to both be at about 1950 feet, but about 1000 feet down from the end of Rwy 04, the land is up at 1965 feet. Computing the slope of that first 1000 feet of runway 04, I get about 0.69 degrees. Maybe the 627 value you’re reading from the SDK is in 1000ths of a degree?