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  • Please see the most recent updates in the "Where did the .com name go?" thread. Posts number 16 and 17.

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Airport locations_Satellite Imagery or FSX?

falcon409

falcon409

SOH-CM-2025
This question at one time seemed like a no-brainer to me. If I use a satellite image of an airport to produce an AFCAD then I would assume that what I have is a fairly accurate representation of that airport, ie; Rwy location, length. . .taxiways, parking ramps, even parking spots if the image is good enough. Maybe there's a slight loss of accuracy simply by virtue of the fact that it's a picture taken from space, lol. . .but still pretty darned accurate I would think. Along with that comes the question of position within FSX. If I'm starting with an existing AFCAD and realize after I've imported the background image, that the rwy in the AFCAD doesn't match the image in length, direction or position in the sim, wouldn't it be logical to accept the satellite image as correct? I've been around FSX and FS9 too long to just accept that they got every single airport spot on, lol. I have redone airports where the satellite image showed the airport close to a mile from the position in the sim....in one case it was further than that. That's one question. . .

Another related question....AFCAD's that are found on download sites like flightsim.com and Avsim profess to have spent long hours analyzing imagery and working with top-notch AFCAD designers to produce the best possible interaction for your flying pleasure, lol. . .yet when I fly with a group where some are using just such an AFCAD...when we land and I taxi back to see them parked on the infield and I'm parked on the ramp. . .well. . .what image did they use that displayed such a different airport? Shouldn't we both be pretty damn close?
 
I'm not sure but I think FS uses a Mercator projection and it wouldn't conform to satalite photos. This would make a difference on location of objects. Just an educated guess.
 
Paul Domingue said:
I'm not sure but I think FS uses a Mercator projection and it wouldn't conform to satellite photos. This would make a difference on location of objects. Just an educated guess.
Click to expand...
Ok, since Mercator Projection tends to distort as it moves away from the equator and is thus less accurate. . .I have to again assume that what I get via a satellite image is closer to the actual airport position and layout. In that case, if I fly to an airport that I built using a recent satellite image and someone in FS9/FSX flies to the same airport with an AFCAD done "by highly trained AFCAD experts" and the airports are significantly different. . . . . .? Is it a no-brainer or not?
 
I would start with true north and then throw in the north deflection to get the runway heading.
But you knew that already, didn't you ed?
 
One way to prove the FSX airport is in its correct location and heading is to use the FAA location and heading info from the charts, go there in FSX and see if it matches. Default FSX seldom does but I am pretty sure the satellite images do.

Dave
 
Sieggie said:
One way to prove the FSX airport is in its correct location and heading is to use the FAA location and heading info from the charts, go there in FSX and see if it matches. Default FSX seldom does but I am pretty sure the satellite images do. Dave
Click to expand...

Thanks Dave. The main gist of this thread was to basically ask the question why people claim to have produced a high quality AFCAD by trained experts, then that airport looks completely different from the one I do based on satellite imagery? What is it they work from? If nothing else, the parking ramps, taxiways and runways should be identical or close to it. I don't cut corners, I spend a lot of time looking at various aerial images and satellite shots to be sure the shapes are as close to exact as I can get them. Until I hear different, I'll assume that mine are correct and theirs aren't.
 
FSX uses the WGS84 world geoid model, which is the basis for GPS as well as many satellite images, vector based data and heightfield (DEM) data. You can reproject other projection types with the appropriate software to WGS84.

This is why you can use GoogleEarth as a source of satellite image data as well as trace roads, coastlines, rivers and so on and use it directly in FSX without the need of reprojecting the source.

Cheers,
Mark
 
Some times people take the aerial imagery and match it to the airport, instead of the other way around... :isadizzy:
 
Meshman said:
Some times people take the aerial imagery and match it to the airport, instead of the other way around... :isadizzy:
Click to expand...
Well, honestly, I asked a related question back when I was first starting to use SBuilderX. One person who posted asked, well what if the satellite image isn't aligned with the AFCAD and someone told him to do just that .readjust the satellite image to match the AFCAD and then make any changes or additions to the AFCAD. I thought it was strange then, but I'm beginning to think that's partly why I see people I fly with landing in the grass but telling me they're on the rwy when we fly into an airport where I've redesigned the AFCAD. The assumption seems to be that FSX got it right and somehow the satellite images are off.

I'm just going to continue doing what I'm doing. I think it's the right way. Thanks everyone for your input. . .good discussion.:applause:
 
I don't know to what effect this has in placement of objects in FSX but there is a 2+1/2 to 3 degree offset or distortion caused by the software's simulation of magnetic variation. In the world of FS The famous Michelson-Morley experiment would have proven the exact opposite results. You can see the result of this offset or foreshortening by sitting in a VC, enter slew and rapidly rotate the aircraft around it's center. You will see the physical world including your aircraft distort or pulsate in-and-out and side-to-side. There is an interesting discussion here.

http://www.fsdeveloper.com/forum/showthread.php?t=289667&highlight=magnetic+variation
 
falcon409 said:
This question at one time seemed like a no-brainer to me. If I use a satellite image of an airport to produce an AFCAD then I would assume that what I have is a fairly accurate representation of that airport, ie; Rwy location, length. . .taxiways, parking ramps, even parking spots if the image is good enough. Maybe there's a slight loss of accuracy simply by virtue of the fact that it's a picture taken from space, lol. . .but still pretty darned accurate I would think. Along with that comes the question of position within FSX. If I'm starting with an existing AFCAD and realize after I've imported the background image, that the rwy in the AFCAD doesn't match the image in length, direction or position in the sim, wouldn't it be logical to accept the satellite image as correct?
Click to expand...

In a word, no. You can't depend on any one thing as correct. You have to use every possible data source you can get your hands on and make your best guess. Note that if you move around runways in an AFCAD you need to fix the approach data, and if there are any associated navaids you need to be careful about those as well. For example, many times there is an ndb or vor located along the extended runway so if you move the runway those navaids will be offset.

I you want fun try working on China. It's only been in the last year that China has updated most of its data to WGS 84 positions. Even with that if you take the coordinates China gives you for a VOR and look at it in Google Earth and Google Maps, you see none of them agree.


scott s.
.
 
Still, the orthoimagery is georeferenced, and once projected correctly, should be an accurate in-sim representation of the actual surface.
 
orionll said:
Still, the orthoimagery is georeferenced, and once projected correctly, should be an accurate in-sim representation of the actual surface.
Click to expand...
Thank you orionll. I'm not doing payware scenery. . .I'm not of that caliber. I do mostly small local airports and sometimes a small regional airport. The extent of my concern with all of this was, and still is, that given a choice between the default placement of airports in FSX and the variation imposed when I overlay a satellite image. . .I will choose the satellite image as correct every time. Also, in MP, If fly into an airport I did and see other aircraft in the group parked in the grass but they say they're on the parking ramp. . .their AFCAD is incorrect, lol.

Again, thanks to everyone who contributed. There is useful information in here above and beyond what I expected and I'm sure others will find it useful and interesting, so thank you.:salute:
 
falcon409 said:
...given a choice between the default placement of airports in FSX and the variation imposed when I overlay a satellite image. . .I will choose the satellite image as correct every time. Also, in MP, If fly into an airport I did and see other aircraft in the group parked in the grass but they say they're on the parking ramp. . .their AFCAD is incorrect, lol.
Click to expand...
Ed, I found this thread interesting because I spent most of my Navy career in photo intelligence. I concur with you that if your AFCAD info is based on satellite-imagery-derived info, it will be more accurate than most of the default FSX airfields. We all know many of them are just quickies to put an airfield where there's supposed to be one. Unfortunately I got lost at some point here and it's probably due to my lack of AFCAD experience. From your quote above I conclude that if you have adjusted an AFCAD for a stock airfield based on satellite imagery but your fellow fliers in a multi-player session have not made the same changes, their final parking spots will potentially look weird to you as will yours look weird to them. Am I correct?
 
TARPSBird said:
Ed, I found this thread interesting because I spent most of my Navy career in photo intelligence. I concur with you that if your AFCAD info is based on satellite-imagery-derived info, it will be more accurate than most of the default FSX airfields. We all know many of them are just quickies to put an airfield where there's supposed to be one. Unfortunately I got lost at some point here and it's probably due to my lack of AFCAD experience. From your quote above I conclude that if you have adjusted an AFCAD for a stock airfield based on satellite imagery but your fellow fliers in a multi-player session have not made the same changes, their final parking spots will potentially look weird to you as will yours look weird to them. Am I correct?
Click to expand...
Correct! What I do when using the image as a template is recreate Aircraft parking ramps, parking lots, etc, exactly as the image shows them, even the building placements are done using the image. What I see from almost every default airport is they have placed a "general" parking ramp in the area where the actual one resides, not the same size, not the same shape and usually not even in the same spot. Most likely that's why in Multiplayer, you see airplanes parked all over the place, airplanes taxiing across the grass infield and taking off on a runway you don't see, but they do. Of course in FS9 it's just as bad or worse.:salute:
 
I read posts from this thread, and am completely clueless as to what it takes to create/modify scenery. But I am SO thankful for all the talent you folks have, and the wonderful creations you provide to this community.

Thank you very, very much!

NC
 
Ed ..... Lets say you have a restaurant and want to invite your friends to eat there one night. Only ............. You moved the restaurant across town and didn't tell them.
Now .... when no one shows up, you are getting mad at them because they went to the old one. This is what you are doing when you move an airport and no one else does.
You are bringing this on your self.
 
JoeW said:
Ed ..... Lets say you have a restaurant and want to invite your friends to eat there one night. Only ............. You moved the restaurant across town and didn't tell them.
Now .... when no one shows up, you are getting mad at them because they went to the old one. This is what you are doing when you move an airport and no one else does.
You are bringing this on your self.
Click to expand...

Joe, sometimes I read posts in this forum...and when I'm done the only response I can come up with is "huh?"...this is one of those times. Are you seriously comparing my correcting airport placement in FSX with moving a restaurant across town and not telling anyone? Really? Obviously you don't agree with my technique and that's fine...there are many who don't...personally, I don't really care. That's the way I do my scenery.
 
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