Now that the chip shortage has begun to ease, and prices on high end GPU's are coming down, I bought an RX-6800-XT card last month, to replace the RX-5500-XT that I installed when I built this machine two years ago. So, it's great, I can finally use MSFS "High" and "Ultra" graphics settings and get 30 fps, EXCEPT at latitudes above about 85° North or South. Has anyone else noticed this? To test it, I set up flight plans that cross directly over the North and South poles, one from Presidente Carlos Ibáñez International Airport in Punta Arenas, Chile (SCCI) to Perth, Australia (YPPH) that crosses almost directly over the south pole, then one from CFS Alert (CYLT) to Suntar Airport in Russia (UENS), that crosses within a couple of miles of the North Pole. At first, the frame rate is as expected, about 30 fps, but once above 85° latitude, the frame rate begins to drop. Above 88°, it's un-flyable, with the frame rate dropping below 5 fps. Even at Alert, which is at 82°N, the frame rate is lower than it should be, 26~28 fps. Not un-flyable, but  less than it would be anywhere in mid-latitudes. Now here's the strange thing: Looking at the performance metrics, neither the GPU nor CPU are seeing maxxed-out utilization. Maybe 50% for the GPU, and 25% for the CPU. Temperatures and power levels are low-average. So why is the frame rate lagging?

Also, has anyone else noticed that the center of Antarctica has no DTM terrain model? It's like a huge hole there, a couple of hundred miles across, with the "ground" at 0' elevation, whereas it should be at about 9.300 feet at Amundson-Scott South Pole Station. Because of this hole in the DTM, and the low frame rate, I guess it would not be possible to model the NZSP airfield there. When I used to play around with custom airport design in FSX, I noticed that runways at very high latitudes would have very strange curves in them. I guess the designers at Asobo haven't figured out how to mitigate these issues in MSFS? I've also just now noticed that the chart display in Little Nav Map is blank above 85° in both North and South latitude.

I would guess it has to do with the Bing Map grid system which doesnt exist at higher latitudes.  There used to be a link in the SDK to the msdn article that described the bing map grid system but I cant find it right now.  maybe someone else knows where it went.

But its my guess that that is the issue.  I've never flown at extreme latitudes so I have no comment on performance.

Just to see how FSX reacts to high latitudes, as a comparison to MSFS, I put the Maule Orion (ski version) on the ground at 90°S, I have FSX with SP1 and SP2. The game loaded with the Maule sitting on the ground at more or less the correct elevation (9,300' at Amundson-Scott South Pole Station), but then I noticed the chassis and CPU fans went to full speed. I opened the Radeon Adrenelin software Metrics page, and immediately saw the problem: CPU Utilization was over 95%, and the power draw was 65 watts, the maximum for the Ryzen 5-3600 CPU, and the CPU temp was 70°C. The GPU was practically idle: utilization about 10%. So the problem with extreme high latitudes at or near the poles seems to be a common issue for both FSX and MSFS. The fact that it's the CPU getting slammed and not the GPU, seems to pretty clearly imply that it's something to do with number crunching of coordinates, probably longitude, rather than rendering of graphics. I am left to wonder, why does FSX include a complete DTM of all of Antartica, right up to the South Pole, whereas MSFS has that huge hole with no DTM for about 300 miles radius (5° of latitude) all around the South pole? It's kind of a shame: it would be cool to have someone generate a Scenery file of Amundson-Scott base, including the 12,000 foot snow runway (NZSP), so that C-130's and Twin Otters could be flown there, as they are in the real world, almost every day in the summer season that the weather is good enough to allow air operations.

This may be related:

I have been doing some sightseeing flights in northeastern Canada these days, including Igloolik (CYGT).
In doing so, I noticed that in the traffic pattern at this airport my framerate dropped from normally 25-30 fps to below 10 fps, on short final even to 1 fps or lower, making it nearly impossible to perform a correct approach and landing.

I then visited several other airfields in northeastern Canada and it turned out that there are other places where my framerate drops like this even though these places are in the middle of nowhere.
These are the airfields CYLC, CYCY, CYAB, CYGT, CYUX, CYHA, CYKG, CYTE, CYAS, CYLU, CYLA, CYDP, CYZG, CYTQ, CYVP, CYFT, CYIK, CYAY, CBQ7, 20K, 01A, and in Alaska PAMH. I have not yet checked other airfields in Canada. Airports I tested at similar latitudes in Norway did not show this behavior.

These are all airfields that were not originally present in MSFS and were added by Navigraph NavData.
At first I thought Navigraph was the cause for this behavior. But even without Navigraph Navdata, these framerate dips show up at the coordinates where the airfields are. They are not equally strong at all places but similar, decreasing on the upwind leg, are lowest on downwind and increase very strongly on final.

It would be interesting to know if this phenomenon also occurs on your high end machine.

 

I did some FSX Antarctica scenery back in the day, IIRC the UK had some good topo maps for doing terrain work and I think there was later an addon of some sort.  I did some modeling of NZWD and NZCM and everything would be a little strange flying there, but I don't recall a frame rate problem in FSX.  Have a friend who was a Herc pilot and did that back when Navy had the mission.  So I tried to replicate with the Capt Sim LC-130.  Of course that's only S77degrees.

 

scott s.

.

 

Edited August 20, 20223 yr by scott967