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bob.bernstein

Why did Microsoft mess up airport locations in Fs2004 ?

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After carefully reviewing and comparing few airports in FS2002 and FS2004 I found out that Microsoft changed coordinates to the airports by putting them in wrong locations.In the attached picture from FSNavigator you see an example of Samos LGSM in Greece.http://forums.avsim.net/user_files/33365.jpgFix01 : Location according to Jeppesen (ARP at runway centerpoint)Fix02 : Runway centerpoint at FS2002Fix03 & Fix05 : Runway in FS2004Fix04 : Runway centerpoint in FS2004 (should have been the ARP)Big Orange circle : the ARP in FS2004Small orange circles : The parking positions in FS2004I really don't understand this. Why did they mess it up ?Couldn't they just have left it as it was ?Now what will the scenery designers do ? Assume and continue correct locations the ones in FS2002 or continue with the wrong ones in FS2004 and design scenery over them ? Its not only a matter of previous scenery location incompatibility; They (default airports) are in the wrong places in regards to real world location. In FS2003 they were much closer to real. :-mad Kyprianos Biris :-cool[link:avsim.com/greece/hvacc]Hellenic vACChttp://vateud.org/images/vatsim-eurs.gifhttp://vatsim.pilotmedia.fi/statusindicato...tor=OD1&a=a.jpg

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The locations of the Greek airports are actually more correct in FS 2004 than they were in FS 2002 and earlier versions. The reason for the apparent discrepency is because the coordinates of Greek airports are provided by Jeppesen relative to the GGRS 87 datum. However, Flight Sim uses the WGS 84 datum for all scenery data which requires that all non WGS 84 data be converted. The result of converting GGRS 87 coordinates to WGS 84 coordinates is the horizontal shift that you noted in your post. FS 2004 is the first version of FS to apply the proper datum conversions to the source data which is why you noticed the change in position from FS 2002 to FS 2004. Here is some information about geographic datums if you're interested: http://www.colorado.edu/geography/gcraft/n...um/datum_f.html

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Thank you Adam.One of the reasons I got confused was that I checked Jeppesen charts and they had the coordinates of (very close to) FS2002.Now what remains for me to understand is how come FS2004 have much different coordinates (by ~1000m North) of real Jeppesen aeronautical data.:-roll Kyprianos Biris :-cool[link:avsim.com/greece/hvacc]Hellenic vACChttp://vateud.org/images/vatsim-eurs.gifhttp://vatsim.pilotmedia.fi/statusindicato...tor=OD1&a=a.jpg

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Again, the coordinate shift is due to the difference between the datum used by Jeppesen to report coordinates in Greece (GGRS87) and the datum used by Flight Sim (WGS84). Versions of Flight Sim prior to FS2004 did not apply any datum conversion and assumed that the Jeppesen provided coordinates were actually given in terms of WGS84, which is incorrect. At LGSM, this resulted in a horizontal error of about 324 meters in versions of Flight Sim before FS2004. There is some free software, named PROJ, that you can use to convert from GGRS87 lat/long to WGS84 lat/long. You can download PROJ here: http://www.remotesensing.org/proj/. Once you download and unzip PROJ, you can use its cs2cs utility to do the conversion. Here's an example of converting the airport reference point coordinates at LGSM from the Jeppesen provided GGRS87 values to the WGS84 values used in Flight Sim 2004:Type in this command line at the command prompt:cs2cs +proj=latlong +datum=GGRS87 +to +proj=latlong +datum=WGS84Then enter the LGSM airport reference point coordinates:26d54'46"E 37d41'25"NThis is the result:26d54'52.415"E 37d41'34.193"N 36.548Note the fairly significant difference between the coordinates you entered and the result of the conversion.

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This is alarming :-)By your explanation, if a real world pilot uses/enters in his CDU the fix coordinates as taken from his Jeppesen charts, he will actually not overfly the correct fixes?Imagine what will this result into, in a GPS approach, where the fixes are supposed to lead you to the runway threshold!Stamatis

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I'm not an expert for the situation in Greece, but this explanation may help:Due to the fact that the earth is not a perfect speroid, countries have their own geographic coordinates, which can deviate from each other by several 100 metres. This has been fine in the recent decades, because there wasn't really an urgent need for a global coordinate system. From reading what's posted here, Greece is still sticking to their local coordinates.The reason that most countries have moved on the WGS84 is GPS. If you want to use GPS you need a uniform coordinate system and WGS84 is what's used. Luckily, this is also what MSFS uses. The problem really is the responsible authority in Greece, not FS2004. I suspect you don't have any GPS approaches, because in aviation you are still using your local coordinate system. If you start using GPS, you'll have to move on to WGS84. That means that the whole set of airport publications will also have to be updated to WGS84 and then will math FS2004. Why Greece hasn't moved on to WGS84 is a mystery to me...Cheers, Christian

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Christian is correct. Here's a little more information on the subject.Read the first page of this NavData NOTAM on the Jeppesen website (http://socrates.jeppesen.com/download/nav_notam/ndlam.pdf). The NOTAM is for Mexico, not Greece, but it does a good job of describing some of the issues and problems faced by Jeppesen and the Mexican government when dealing with the changeover from a local datum to WGS-84. Here's an excerpt:--quote--ATTENTION: Mexico is currently in the process of converting its coordinate information to WGS-84 reference datum on a gradual basis. They recently began issuing new WGS-84 coordinates for Airport Reference Points (ARPs) and runway ends at various airports around the country while retaining established coordinates for navaids and airspace fixes. Eventually, all coordinates in Mexico will be converted to WGS-84. During the interim period, and as a result of a mixture of old and new coordinates, Jeppesen has encountered NavData coding problems related to track misalignments and route discontinuities. When such a situation occurs, and depending on the circumstances, some coding procedures may be omitted from the database or may be indicated in Jeppesen NavData NOTAMs as being unusable. The extent of the coordinate problem may vary, and might differ from location to location. Refer to future NavData NOTAMs for information about specific procedures.Jeppesen will contact Mexico authorities and attempt to resolve the situations affecting database coding. Applicable flight information will continue to be published on Jeppesen Airway Manual charts.BACKGROUND: Countries around the world are expected to convert the coordinates used in their airspace systems to the WGS-84 reference datum. The conversion process can vary from country to country. Ideally, all coordinates in a country's airspace system would change simultaneously (navaids, airspace fixes, runway ends, ARPs, ect). In some countries the official conversion to WGS-84 is made gradually, over an extended period of time. The result of a gradual conversion is a mix of coordinates based on different geo-reference datums. When a partial or gradual conversion to WGS-84 is made, the resulting mixture of coordinates based on different datums can cause relational and alignment problems within the electronic data provided for FMS and GPS navigational uses. Most likely to be affected are the coded instrument procedures in the terminal environment (approach, departure and arrival procedures). UFN.--end quote--Jeppesen has a list of countries using WGS-84 coordinates. Note that Greece isn't on the list. http://www.jeppesen.com/wlcs/index.jsp?sec...ions_wgs84.htmlGarmin has some interesting information in the manual for their GPS 500 (the real one, not the one simulated in FS 2004). http://www.garmin.com/manuals/30.pdf. Here's an excerpt:--quote--Configuration settings for position format and map datum are also provided. Position formats include latitude/longitude, MGRS and UTM/UPS. The NavData

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Christian & Adam thank you very much. Very helpfull information indeed. In the beginning of my post I thought about moaning against MS, then about Jeppesen and now I'll end up moaning about our Ministry of Transport / Civil Aviation Athority :-rollThank you ;-)Kyprianos Biris :-cool[link:avsim.com/greece/hvacc]Hellenic vACChttp://vateud.org/images/vatsim-eurs.gifhttp://vatsim.pilotmedia.fi/statusindicato...tor=OD1&a=a.jpg

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Very interesting information.However, there is one thing that bothers me.That's called LGAV. LGAV was not present in FS2002, but is present in FS2004 by default.Since there was no LGAV in FS2002, we had to make one. So I did. And I placed it based on the AIP coordinates published by the Greek CAA.If FS9 uses the new reference system and we take it for granded that the HCAA uses the old reference system, and there is so much difference between the two coordination systems, how come LGAV is at EXACTLY the same position??Can the difference between the 2 datums affect only some airports and not others?George DorkofikisAthens, Greece

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The result of a gradual conversion is a mix of coordinates based on different geo-reference datums. When a partial or gradual conversion to WGS-84 is made, the resulting mixture of coordinates based on different datums can cause relational and alignment problems within the electronic data provided for FMS and GPS navigational uses. Most likely to be affected are the coded instrument procedures in the terminal environment (approach, departure and arrival procedures).The above just confirms that my worries expressed in my message above are very well founded :-( It basically means that if someone places his aircraft at an airport reference point, a navaid or a fix, his GPS/FMS will NOT display the same coordinates as listed in the appropriate Jeppesen plate. I find this extremely "unprofessional", to put it mildly, but who am I to worry?Stamatis

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George the default FS2004 LGAV Venizelos is not exactly in same position. It is off by your excellent freeware LGAV for FS2002 (where it was absent from as default) by 50~100 meters.Default FS2004 LGTS Makedonia (Greece's third in size after LGAV and closed LGAT) is also very close. FS2004 LGTS is off by 50~100m to the West from default FS2002 LGTS. On the contrary, FS2004 LGIR Kazantzakis to the South is about 1000 to 800m North of FS2002 LGIR. So I guess WGS84 with GGRS87 produces different kind of dicrepancies depending on Georgaphic location. Sorry Adam have not had the time to test them on PROJ Kyprianos Biris :-cool[link:avsim.com/greece/hvacc]Hellenic vACChttp://vateud.org/images/vatsim-eurs.gifhttp://vatsim.pilotmedia.fi/statusindicato...tor=OD1&a=a.jpg

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Probably you are right.I used the default startup position of FS9 and compared the a/c position against the THR of 03R. It is off, but not that much at that point...But then again, who knows if the default LGAV is correct at size!!!(At least I know mine is accurate within 5m) :-)Cheers,George DorkofikisAthens, Greece

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George,Good observation. After a little research, I found that a few of the Greek airports use WGS-84. Presumably LGAV does because it is so new. I put together a little table to help you determine the status of the rest of the Greek airports in FS2004. You can view the table here: http://www.speakeasy.org/~zof/AvSim/GreekAirportDatums.htm. By reading the "Shift" column in the table, you can see that any of the airports using the GGRS 87 datum experience a shift of about 320 meters from where they were placed in FS2002 and earlier. The Lat/Lon (WGS84) columns represent the latitude and longitude of the airport reference point after conversion to WGS 84. The Lat/Lon (source) columns represent the latitude and longitude of the source data in the original datum before conversion to WGS 84.Regards,Adam

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That's very helpfull!THANK YOU VERY MUCH!George DorkofikisAthens, Greece

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