Airport locations_Satellite Imagery or FSX?

[falcon409]

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?

[Paul Domingue]

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.

[falcon409]

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.
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?

[JoeW]

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?

[falcon409]

Yep, thanks Joe!:salute:

[Sieggie]

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

[falcon409]

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

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.

[roger-wilco-66]

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

[falcon409]

Thanks Mark, that works for me.:salute:

[Meshman]

Some times people take the aerial imagery and match it to the airport, instead of the other way around... :isadizzy:

[falcon409]

Some times people take the aerial imagery and match it to the airport, instead of the other way around... :isadizzy:
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:

[Paul Domingue]

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

[scott967b]

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?

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.
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[orionll]

Still, the orthoimagery is georeferenced, and once projected correctly, should be an accurate in-sim representation of the actual surface.

[falcon409]

Still, the orthoimagery is georeferenced, and once projected correctly, should be an accurate in-sim representation of the actual surface.
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:

[TARPSBird]

...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.
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?

[falcon409]

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?
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:

[Navy Chief]

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

[JoeW]

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.

[falcon409]

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.

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.

[JoeW]

Whats key in my thread is "This is what you are doing when you move an airport and no one else does." The guys you are flying with don't know you moved the airport or don't have your airport. Thats why the are landing on the grass on your computer. What do you expect?

[falcon409]

Whats key in my thread is "This is what you are doing when you move an airport and no one else does." The guys you are flying with don't know you moved the airport or don't have your airport. That's why the are landing on the grass on your computer. What do you expect?
I expect that I'll continue doing exactly what I've been doing. The guys I fly with know exactly what I've done because I let them know prior to our flights and the fact that they are parking on the grass is no mystery to me JoeW. . .I'm well aware of the fact that they are parked that way because their AFCAD is incorrect. They aren't going to worry about it because the airports we fly to. . .in 99% of the cases, we will never fly to again as a group and for us that's the only time it's noticeable.

The fact that it's noticeable to me is the reason I asked the original question, which basically was and still is. . .if folks are going to go to the trouble of remaking an airport, why not do it correctly and use satellite imagery to base their work on rather than simply redoing an old AFCAD that was incorrect to begin with? That's the way I see it, I don't care if anyone else has a problem with it, they (you) are welcome to disagree as much and as often as necessary. . .it is your right to do so. Just don't expect me to suddenly say. . .Wow, ya know what. . .you're right!:salute:

[TARPSBird]

Ed, I would like to know how you use satellite imagery as a template for your airfield mods. Some time ago I started to use AFCAD 2.21 to build Naval Air Station Glenview in FS9. As you already know from FSX, it wasn't a case of modifying a default airfield because Glenview wasn't included in FS9, it's long gone in real life and replaced by upscale condos and shopping malls. I didn't have Google Earth installed at the time so I used a topographic map, an old airport diagram, and a couple good aerial pics I got from websites. Got the two runways positioned just right, then some family events occurred and I never went back to the project. I would like to finish it so it looks at least as complete as the Glenview you did in FSX so any suggestions are welcome.

[JoeW]

Somehow Ed, I was reading this thread as a complaint on your part about the people you were flying with in multiplayer parking on the grass and landing and taking off on the grass. On re-reading this thread I don't see it that way. I'm sorry about some of my replies as I read it wrong.
What I do is use Skyvector to find the airport and download a diagram with the parking areas, names of the taxiways, and actual coords of the airport and runway heading with the north deviation. You can import that into ADE and after re-aligning the runway to fit the diagram you can alter the taxiways to fit the diagram. Thats about as close as you can get.

[fliger747]

In some areas the magnetic drift has been fairly rapid, with the FSX base now being off several degrees from the current magnetic headings for runway and approach alignment. This is especially true here in Alaska. Not sure what Prepare3d uses?

T

[falcon409]

Ed, I would like to know how you use satellite imagery as a template for your airfield mods. Some time ago I started to use AFCAD 2.21 to build Naval Air Station Glenview in FS9. As you already know from FSX, it wasn't a case of modifying a default airfield because Glenview wasn't included in FS9, it's long gone in real life and replaced by upscale condos and shopping malls. I didn't have Google Earth installed at the time so I used a topographic map, an old airport diagram, and a couple good aerial pics I got from websites. Got the two runways positioned just right, then some family events occurred and I never went back to the project. I would like to finish it so it looks at least as complete as the Glenview you did in FSX so any suggestions are welcome.
My main program is SBuilderX. That's how I capture the satellite imagery I want. I also do excludes and flattens from there, add water poly's (lakes, rivers, etc) and add or change landclass, among other things. For the actual AFCAD I use AFX. It's in this program that I insert the satellite image. . .when you select that option in AFX it requires that you input the correct coordinates for the image (contained in a file within SBuilderX). Once you do that, the image is resized and positioned correctly and you can start from that point to adjust the rwy/taxiways/parking ramps. Normally I delete everything except the rwy simply because it's easier to redo the taxiways and parking ramps than try to adjust and they're usually way off anyway.

[TARPSBird]

Ed, thanks for the info, it's most appreciated. :salute: You're way more up on this airfield construction than I am, so beware, I may ask you more questions in the future. My job #1 is finishing my NAS Glenview in FS9 before I attempt anything in FSX. I'm thinking Sky Harbor Airport in my hometown of Northbrook, IL might be a nice entry-level FSX project. I would definitely have to include the cool arch-roof hangar.
http://members.tripod.com/airfields_freeman/IL/Airfields_IL_Chicago_N.htm#skyharbor

[falcon409]

Ed, thanks for the info, it's most appreciated. :salute: You're way more up on this airfield construction than I am, so beware, I may ask you more questions in the future. My job #1 is finishing my NAS Glenview in FS9 before I attempt anything in FSX. I'm thinking Sky Harbor Airport in my hometown of Northbrook, IL might be a nice entry-level FSX project. I would definitely have to include the cool arch-roof hangar.
http://members.tripod.com/airfields_freeman/IL/Airfields_IL_Chicago_N.htm#skyharbor
That does look like a great little airport with very recognizable buildings. Are those original buildings still in use? (Just finished reading the entire article and that answered the previous question, lol) I'd be glad to answer any questions you have in the future. Best of luck with Glenview and your future projects!:salute:

[TARPSBird]

Ed, thanks again and allow me to share a memory with you. When I was a kid we lived on the approach to Rwy 17 at Glenview, little more than a mile up the road. This was long before cable TV and any aircraft landing on 17 would cause our TV picture to go totally weird. Then in 1957 my grandma and uncle moved to a new house less than a mile from Sky Harbor and we'd still get TV interference from the planes. :icon_lol: Except now the planes were smaller and they had to fly darn near right over the house to mess up the TV.
Back in the 1930's a local airline named Gray Goose used to fly Ford Tri-Motors out of Sky Harbor. I wish I had at least one good pic of a Gray Goose aircraft, that's one company that's missing from that vast assortment of Tri-Motor repaints that Garry Smith has done.