FSX Terrain and Weather Interaction

I have been flying a lot in FSX in the mountains of central Idaho using various general aviation aircraft. As a resident of the area I am very aware of the weather in the region. I have seen, now that FSX (and the real world Northern Hemisphere) has moved in to Spring, something I rarely noticed at tubeliner altitudes.

I am curious about how the FSX "Terrain Engine", for lack of a better description, and the FSX "Weather Engine" (in this case Active Sky Evolution...ASE) interact to display what I see on the ground as I fly over it?

For example, in the recent past we had a "warm spell" here in Idaho and it corresponded very nicely with the turn of the season (for real and in FSX) to Spring. In FSX I saw quite a lot less snow on the mountains during this period. However, last week was particularly rainy in the lower elevations for real and snow in the mountains above 6,000 feet. Now, flying over the exact same scenery at the same season in FSX I am seeing snow in mountain meadows that were green in FSX two weeks ago. So FSX has "reacted" to what the real weather has done.

A more specific example is the airstrip at Pine Idaho, 1U9. During the week of warm weather I drove to Pine and saw for myself that there was no snow around the airfield at all. It had all melted off nicely. I flew in FSX just to see how FSX would display the airfield and terrain and it matched very well, some snow at higher elevations but none on or near the airfield. I was impressed with how FSX reacted to the season and the real weather...and ASE.

After a week of rain and higher elevation snow I drove up to Pine again (it's only a 40 minute drive for me) and saw spots of snow at lower elevations and the remains of snow along the fringe of the grass runway and airfield boundary. Went home and loaded up FSX and sure enough, the edge of the runway was showing a fringe of snow. FSX had somehow taken the real information and weather history...perhaps from ASE somehow or a real world embedded link somewhere in the FSX code...and was displaying the airfield very well and, for the most part, accurately.

So now I have this wondering about how FSX and the real world are able to interact so well...at least to me it seems that way. If it were purely a "time of year" or specific day thing there is no way FSX could know to display snow on a field where only a week before it had displayed none. Somehow FSX "knew" a field it depicted the terrain as clear of any snow earlier had received snow and now showed it with a snow "fringe" on the edge of the runway and parking area. I thought perhaps ASE was somehow looking at the real world weather history and affecting the airfield with a snow fringe. To test this I ran FSX without any weather engine, choosing "Clear" in the weather options and not even starting ASE. Snow fringe was still there. I realize FSX won't always depict a field that way it looks at the moment, but I am very impressed that it seems to have a "knowledge base" within it's code somewhere that remembers what has happened in an area weatherwise.

Any coding gurus out there know how FSX interacts to display terrain that is reasonably accurate with the weather, past and present?

Randy
 

Ronald

Resource contributor
Hello Randy, thank you for sharing this amazing weather and terrain interaction story here, especially since I myself never have noticed it so up and close as you describe here..

Any coding gurus out there know how FSX interacts to display terrain that is reasonably accurate with the weather, past and present?
I'm not a coding guru in that area of FSX (yet) but as an experienced ICT-er, i can offer you a few suggestions so you can find the answers yourself

In your current situation you now have AND ASE AND FSX default build-in real-time weather updates, which could modify your scenery at the same time.
If you want to investigate this phenomena further and deeper, may I suggest the following steps:
A - Find out if ASE fully replaces the internal FSX-weather and scenery engine or that ASE works together,to compliment the internal FSX-weather and scenery engine?
In order to see how this work (under the hood) you can fully uninstall ASE first, and then see what happens when you repeat the above steps again.

B - Also ask this question also on the ASE forums, since they have created the ASE product kand knwo what is does (under-the-hood):
- https://www.hifisimtech.com/forums/

I'm curious to your test-results
 

arno

Administrator
Staff member
FSDevConf team
Resource contributor
Hi,

As far as I know the terrain system does not take weather into account. Within the seasons.bgl file it is defined for each month what season the terrain should have (e.g. hard winter = snow, spring, summer, etc). Based on that the terrain system will pick a different texture to render the specific landclass. The shape of the terrain (e.g. steepness) is also taken into account to show a realistic terrain.

When it is snowing I think the engine for landclass does switch to hard winter automatically, but for photo scenery that doesn't happen. So that might be the only weather interaction there is.
 
...it is defined for each month what season the terrain should have (e.g. hard winter = snow, spring, summer, etc). Based on that the terrain system will pick a different texture to render
Thanks Arno, for the reply. Seems to me, though, if the rendered landclass texture were based solely on the current weather (clear and sunny...no precip) and current month/season then a green mountain meadow would always display as a green mountain meadow, right? In my example, two weeks ago I overflew a green mountain meadow in clear skies and no precip at all. It displayed green. After last weeks real time rain showers and snow in the mountains I again overflew the same meadow in the sim, but after the storm and again in clear skies and no precip (identical conditions to the earlier overflight), but this time although the meadow was still mostly green, it had a "fringe" of snow around it. The only reason I noticed was this meadow is one of my "landmarks" for a VFR approach to Landmark USFS Airstrip, 0U0. It was not snowing at the time, nor had it been for a day or so...in the real world. Something, seems to me, "told" FSX that it had snowed recently and to place the "fringe of snow" around the meadow (landclass texture).

Seeing that "condition" at Landmark in the sim prompted me to make the real world trip back up to Pine to check out 1U9 since I had been there a 2 weeks before during the warm spell and noted no snow around the field. At the second trip there was snow bordering the real world field, but not on it. The sim displayed the same appearance, snow border, no snow on the Airport itself. I will watch for the same conditions (we have rain in the forecast...snow in the mountains...typical Spring weather in Idaho) and try to get screenshots to better illustrate my question.

@Ronald ...by suggesting that I uninstall ASE (not simply "not start it" and fly with FSX weather set to Clear and Sunny) are you thinking that ASE does "maintain" a history of what the real world weather has been and inject a "fringe" of snow somehow on to the landclass? I will pose the question over at HiFi as well and see what they say.

Thanks to both for your response.

Randy
 
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Ronald

Resource contributor
...by suggesting that I uninstall ASE (not simply "not start it" and fly with FSX weather set to Clear and Sunny)
You could also try that first, simply not starting it and see what happens.
I merely suggested uninstallation as a way to be sure nothing else then FSX-native software is running on you computer.

are you thinking that ASE does "maintain" a history of what the real world weather has been and inject a "fringe" of snow somehow on to the landclass?
I do not know this, that is something you can as at the Hifisim forums over here:
- https://www.hifisimtech.com/forums/
 
Thanks again for the reply Ronald. I did post over at the HiFi Forums about this. There's only been one response...still waitin to see others...from an Active Sky Beta tester who does not think what I am seeing is influenced by Active Sky Evolution. He said ASE influences the weather through two files that don't, he believes, interact with FSX except to display weather phenomenon.

https://hifisimtech.com/forums/showthread.php?9473-Does-Active-Sky-Evolution-Remember-Real-World-Weather-History

Seems odd to me. Three things, as far as I know, determine what terrain landclass FSX shows over any given point in the sim...season, month, and hemisphere in the sim. Weather in the sim (either one of the "canned" settings, a third party weather engine like ASE, or the Real World Weather engine built in to FSX) affects the terrain display to a certain degree. If the weather tells FSX that it is snowing FSX paints the world white. Raining? FSX makes the world wet. Yet I am seeing "clear and sunny-paint the meadow green" followed by a period of snow in real life that FSX does not know happened and then "clear and sunny-give the meadow a snowy fringe". Doesn't make sense unless FSX has been "told" by something that it snowed while it wasn't being used. Wish the ACES team was still active or the ESP series of documents explained how FSX works better.

Season, month, and hemisphere haven't changed from the first flight over a green meadow and the second flight over a snow fringed meadow. The weather during both flights was the same also. The only thing that was different was during a period when I did not fly. It had snowed for real in this area. My sim doesn't know that, though, since I did not fly during a period of precipitation of any type. Since the meadow did not have a snow fringe before and has one now that implies that FSX somehow knew that it had recently snowed in Idaho (or guessed I suppose...some type of backward looking prescience) either based on it's own weather engine history or ASE's weather engine history and that history affected the appearance of the snow fringe.

Randy
 
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Ronald

Resource contributor
I did post over at the HiFi Forums about this. There's only been one response...still waiting to see others
As long as you do not get an honest and open answer straight from the Active Sky Developers themselves, one can only continue to reverse-engineer it by yourself and
see how it works, by systematically breakdown it functionalities and investigate them to the bottom and share the results with the world.

He said ASE influences the weather through two files that don't, he believes, interact with FSX except to display weather phenomenon.
Which 2 files? and what functionality do they influence?

Three things, as far as I know, determine what terrain landclass FSX shows over any given point in the sim...season, month, and weather in the sim
Where did you get this knowledge from? and is it accurate and complete since the "official ESP FSX SDK" is far from being that.

That tells me that FSX somehow knew this either based on it's own weather engine history or ASE's weather engine history and that history affected the appearance of the snow fringe.
One idea comes to mind to make this process fully transparant:
- Download and install Wireshark https://www.wireshark.org/
- Start Wireshark and start a internet-network packet capture trace
- Fire up FSX and select a flight with real-world weather.
- Fly around a little in that area you are investigating and land the plain at the beginning of your journey
- Close FSX again.
- Save and store the WireShark packet-capture file for later analysis.

That is one way to find out how you can find out whether:
- Which servers FSX is using to get its METAR data from?
- FSX only downloads the current METAR of the area you are flying.
- FSX also taps into an historical archieve of METAR data, and stores it somewhere on your harddisk.
 
This was his reply in it's entirety Ronald...

Hi Randy,

Thanks for such a great and detailed post. From what I know, AS products have based weather on the current data gathered and provided via the servers. Currently AS derives the weather from a file called "LastDownloaded.Wx" or "current_wx_snapshot.txt."

I wish it were the case that ASE applied the patchy textures you described but they were most likely not processed by AS. And no, I do not think you are off your rocker.

Rob
I actually had edited my post, apparently after you posted...I changed "weather in sim" to "hemisphere" (since it is now Fall in the Southern Hemisphere) and gave weather a role in my next sentence instead...

"Weather in the sim (either one of the "canned" settings, a third party weather engine like ASE, or the Real World Weather engine built in to FSX) affects the terrain display to a certain degree."

I am basing the three factors on what Arno said above and my own practical experience in the simulator, thus the phrase "as far as I know". I could have just as easily said "I believe". I certainly have found no official documentation that states how FSX chooses what landclass/terrain/cover to display, but my search is far from over.

I have downloaded Wireshark as you suggested, but need to run some errands and then will give it a go and see what results are given and reply here.

Thanks again Ronald. Sorry to be such a pain. My curiousity truly will "kill a cat" someday... :)

Randy
 

Ronald

Resource contributor
Thanks for posting the ASE forum reaction over here Randy.

I certainly have found no official documentation that states how FSX chooses what landclass / terrain / cover to display, but my search is far from over.
Like so many other lines of official documentation are missing right.. the stuff which it only present inside the heads of former ACES Studios (or DTG) developers,
and/or other individuals who have hacked /reverse-engineered their way into belly of the beast.. the heart of the FSX flightsimulator.

TIP: If you are ready to dig deeper into the inner working of FSX.EXE, you can always download the free SysInternals Suite over here:
- https://docs.microsoft.com/en-us/sysinternals/downloads/sysinternals-suite

Inside this awesome free package one can find - among others - the following tools:
DISK MONITOR - https://docs.microsoft.com/en-us/sysinternals/downloads/diskmon
This tool gives you an WINDOWS API level insight into which information is read from / written into which files on your computer.

PROCESS MONITO - https://docs.microsoft.com/en-us/sysinternals/downloads/procmon
This tool gives you an WINDOWS API level insight in all registry key whic are being queried, read and written


Thanks again Ronald. Sorry to be such a pain. My curiosity truly will "kill a cat" someday...
You know what they say right.... no pain, no gain... and your curiosity will only gain more insight on stuff you want to know.
 
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