Ray Proudfoot

20 years on and Prime Meridian problem still exists

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Back in the days of FS98 - 20 years ago - the sim would stutter as you flew over the Prime Meridian in London. With all the advances in flight sim since then I'm really surprised the problem is still there in P3D.

I noticed it when slewing across London when testing performance in P3D v3.4. After slewing up to 1500ft at Rwy 28 at London City airport I increased speed to 240kts and started to move towards Canary Wharf. As I approached the buildings P3D stuttered really badly for a couple of seconds. I wondered what could be causing it but finally the penny dropped.

The aircraft is crossing the Prime Meridian. I remember FS98 (and maybe even earlier versions) having this problem but I would have thought it would have been solved by now. Looks like the same basic engine is driving P3D as drove FS98 and probably all versions since.

It won't happen just in London of course but anywhere where you cross from one hemisphere to the other. Anyone else noticed this?

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Funny, I always just put this down to London being a performance hog. Interesting......

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I would report this bug in the LM forum. It may help them fix it for the next version.

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I will report it but it may be down to the design. If Microsoft couldn't fix it in 3 versions after FS98 then maybe it's not a bug but a feature.

Maybe it only happens in London with the complex scenery. Easy enough to check. Just find another airport close to the PM and fly or slew over it.

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1 hour ago, Ray Proudfoot said:

Back in the days of FS98 - 20 years ago - the sim would stutter as you flew over the Prime Meridian in London. With all the advances in flight sim since then I'm really surprised the problem is still there in P3D.

I noticed it when slewing across London when testing performance in P3D v3.4. After slewing up to 1500ft at Rwy 28 at London City airport I increased speed to 240kts and started to move towards Canary Wharf. As I approached the buildings P3D stuttered really badly for a couple of seconds. I wondered what could be causing it but finally the penny dropped.

The aircraft is crossing the Prime Meridian. I remember FS98 (and maybe even earlier versions) having this problem but I would have thought it would have been solved by now. Looks like the same basic engine is driving P3D as drove FS98 and probably all versions since.

It won't happen just in London of course but anywhere where you cross from one hemisphere to the other. Anyone else noticed this?

Wow Ray, you should get some special recognition for this. :happy:

  I never would have guessed in a million years that this would be the culprit.  Like others, I've had stutters in that region as well, but like everyone else, I chalked it up to being in a dense metro area.  This also raises the question of whether ALL simulators would be affected by this?

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You should see what happens in the bermuda Triangle. :blush:

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I went east and west across the prime meridian several times in both directions at several Latitudes of varying scenery in repeated tests and recorded no changes other than a shift in the stars location at night. Have you tried the prime antimeridian?

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Interesting observation. I always thought it was something to do with one of the autogen buildings near the London City airport. I will have to do a few more checks in a few other locations and see what happens.

Interestingly a lot of major cities fall into a meridian. Amsterdam, Paris, Madrid, all have major performance issues. At least for me.

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2 hours ago, SteveW said:

I went east and west across the prime meridian several times in both directions at several Latitudes of varying scenery in repeated tests and recorded no changes other than a shift in the stars location at night. Have you tried the prime antimeridian?

Steve,

I'm surprised you can't replicate this at EGLC. During my AM testing I slewed across the PM every time and every time I had the same problem. I only went east to west and so far I haven't tested the problem elsewhere.

The problem of testing 180W/E is finding an airport close enough so you don't need to slew for very long. But anywhere in the Pacific close to it is not going to have complex scenery. London is unique.

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1 hour ago, RancidViper said:

Interesting observation. I always thought it was something to do with one of the autogen buildings near the London City airport. I will have to do a few more checks in a few other locations and see what happens.

Interestingly a lot of major cities fall into a meridian. Amsterdam, Paris, Madrid, all have major performance issues. At least for me.

But those cities don't straddle the Prime Meridian. It's the change from one hemisphere to another I believe is the key. I think there's a lot of scenery files being loaded as you cross it and together with the complex London scenery that is what is causing the stutters.

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I am not an expert , but might it be that there is a little overlap from start and finish, so underground/object are being calculated twice : eg 0 and 360 degrees

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3 minutes ago, GSalden said:

I am not an expert , but might it be that there is a little overlap from start and finish, so underground/object are being calculated twice : eg 0 and 360 degrees

Many years ago there was a utility that could read BGLs and show the lat/lon they covered. Maybe that is still available in the Library.

The BGLs around EGLC won't cover 360 degrees of course. They'll either be 0-1 degrees east or 0-1 degrees west.

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Very intersting. I always get stutters right about there when I fly the CLN SID out of EGKK. Does that match these findings? 

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3 minutes ago, andreh said:

Very intersting. I always get stutters right about there when I fly the CLN SID out of EGKK. Does that match these findings? 

Gatwick is west of the meridian, Clacton is east. Easy to check - press Shift+Z to show lat/lon top right.

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I have never noticed this. A few moments ago I passed the meridian in the FSL A320-X on a BPK departure on my way from LHR to CPH and there was not the slightest of stutter to observe. 

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