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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1 minute ago, SierraDelta said:

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. 

That departure takes you well north of central London. I'm not saying it happens everywhere where the prime meridian runs. Also, you're at least 3000ft up. It may not be as easy to see.

Load the Cub, go to Rwy 28 at EGLC, slew up a few hundred feet and move westward. It happens for me, it should for you and all P3D users.

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1 hour ago, Ray Proudfoot said:

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.

Ray I mean like a wrap around underground which overlaps where they touch ...

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44 minutes ago, GSalden said:

Ray I mean like a wrap around underground which overlaps where they touch ...

Sorry, I don't follow. Why would there be any scenery underground? There are layers of course but the bottom-most would still be located in the surface of the earth. I don't see why there would be any overlapping but without the tools to check we're just guessing.

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3 hours ago, Ray Proudfoot said:

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.

I've slewed and I've flewed back and forth across 0 right over the city, tried starting from saved flights and going in from the menu and seen nothing.

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I've just checked again using the default Cub. Approaching from the east the stutters are very obvious. Once past them in the western hemisphere I rotate the aircraft 180 degrees and head east. Still very noticeable.

I also slewed the aircraft to 52.30.00N and tested it there. You have to watch more carefully but the stutters are still present. In normal circumstances you would never spot them. Only in London are they obvious because of the number of objects present.

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I have noted a stutter when approaching the Canary Wharf buildings after departure from Runway 27 at London City airport (in P3D v3.3.5). However, I had assumed that it was because of the detailed scenery that I have active in the area (UK2000 London City Xtreme/UK2000 London Heathrow Xtreme/UK2000 VFR Airfields Volume 1/Aerosoft VFR London X), and the high density of AI planes that I have operating at all times.

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Hi Ray!

I think it urgent that you report this bug to LM. Otherwise we may miss their adjacent new release:dry:

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I've even tried with/without weather over London and at several places down to North Africa, graphs of frame rate show no anomalies.

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Just made some circles over London coming from different sides. No issues here...

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15 minutes ago, Richard McDonald Woods said:

Hi Ray!

I think it urgent that you report this bug to LM. Otherwise we may miss their adjacent new release:dry:

Done this morning. No response as yet.

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