P3D v6 Request for help on the data produced by Pete Dowson's Makerwys

[DragonflightDesign]

Makerwys produces the following (cut down) output for EGAC (Belfast City):-

<ICAO id="EGAC">
<ICAOName>Belfast City</ICAOName>
<Country>United Kingdom</Country>
<City>Belfast</City>
<File>Scenery\0501\scenery\APX46120.bgl</File>
<SceneryName>0501 Base</SceneryName>
<Longitude>-5.872500</Longitude>
<Latitude>54.618057</Latitude>
<Altitude>14.99</Altitude>
<MagVar>-3.000</MagVar>
<Runway id="04">
<Len>5989</Len>
<Hdg>37.750</Hdg>
<Def>Asphalt</Def>
<ILSFreq>108.10</ILSFreq>
<ILSHdg>37.75</ILSHdg>
<ILSid>IHBD</ILSid>
<ILSslope>3.00</ILSslope>
<ILSname>ILS/DME 04</ILSname>
<Lat>54.611370</Lat>
<Lon>-5.880568</Lon>
<FSStartLat>54.611599</FSStartLat>
<FSStartLon>-5.880289</FSStartLon>

Specifically, I can't make sense of the lat-lon fields. Shift-Z in the sim shows EGAC at N54 36.72 / W5 52.79 (actually the end of rwy 04), but that's nowhere near any of the figures produced by makerwys. The docs say that <latitude> and <longitude> (not <lat> or <lon>) represents the centre of the runway, but it doesn't appear to be so. I guess that FSStartLat and FSStattLon are the top-left corner of the BGL? Can someone help with what exactly the various lat-lon figures represent?

Thank you.

-Dai

 

[GaryGB]

Hello:

Probably the RWY "Start Location" ?

https://forum.simflight.com/topic/98842-moving-aircraft-to-gates-or-runways/

https://www.prepar3d.com/SDK/Environment Kit/BGL Compiler SDK/Compiling BGL.html#RunwayStart


C:\Program Files\Lockheed Martin\Prepar3D v6 SDK 6.1.10.31609\World\Scenery\bglcomp.xsd

Open in NotePad++ -> Lines: 157 - 173

<xs:complexType name="ctRunwayStart">
    <xs:attribute name="end" form="unqualified" type="stEnd" />
    <xs:attribute name="lat" form="unqualified" type="stLatitude" use="required" />
    <xs:attribute name="lon" form="unqualified" type="stLongitude" use="required" />
    <xs:attribute name="alt" form="unqualified" type="stAltitude" use="required" />
    <xs:attribute name="heading" form="unqualified" type="stHeading" use="required" />
    <xs:attribute name="type" form="unqualified" type="stStart" />
  </xs:complexType>
  <xs:complexType name="ctStart">
    <xs:attribute name="number" form="unqualified" type="stRunwayNumber" />
    <xs:attribute name="designator" form="unqualified" type="stDesignator" />
    <xs:attribute name="lat" form="unqualified" type="stLatitude" use="required" />
    <xs:attribute name="lon" form="unqualified" type="stLongitude" use="required" />
    <xs:attribute name="alt" form="unqualified" type="stAltitude" use="required" />
    <xs:attribute name="heading" form="unqualified" type="stHeading" use="required" />
    <xs:attribute name="type" form="unqualified" type="stStart" />
  </xs:complexType>

https://www.fsdeveloper.com/wiki/index.php/BGL_file_format_(FSX_airport)


Probably Pete Dowson's FSUIPC Offsets Documentation and Patrick Germain's BGLViewer may shed more light as well.

GaryGB

 

[DragonflightDesign]

Thank you. I searched high and low and low and high and somehow completely missed that bit in the SDK BGL docs

 

[Bavarello]

Specifically, I can't make sense of the lat-lon fields. Shift-Z in the sim shows EGAC at N54 36.72 / W5 52.79 (actually the end of rwy 04), but that's nowhere near any of the figures produced by makerwys. The docs say that <latitude> and <longitude> (not <lat> or <lon>) represents the centre of the runway, but it doesn't appear to be so. I guess that FSStartLat and FSStattLon are the top-left corner of the BGL? Can someone help with what exactly the various lat-lon figures represent?

Hello,
The key point is that the <Latitude> and <Longitude> fields in the ICAO block refer to the ARP—the Aerodrome Reference Point—not the runway center or ends.

The ARP is typically located near the geometric center of the airport or at a designated administrative location, and not necessarily aligned with any runway threshold or midpoint. That’s why the coordinates 54.618057 / -5.872500 are quite different from the end of Runway 04 that you see with Shift-Z.

As for the <Lat> and <Lon> inside the <Runway> block, those usually refer to the ILS antenna location or the runway threshold, depending on how the data was compiled. The <FSStartLat> and <FSStartLon> values are often used to define the starting position for aircraft on that runway in Flight Simulator—essentially where the aircraft is placed when you select that runway for departure.

So in summary:

• <Latitude> / <Longitude> = ARP (Aerodrome Reference Point)
• <Lat> / <Lon> in <Runway> = ILS or threshold location
• <FSStartLat> / <FSStartLon>; = aircraft spawn point on the runway
  
  

The Aerodrome Reference Point (sometimes called the Airport Reference Point) is the designated geographic location of an airport. It’s not just a random spot—it’s carefully chosen based on international standards.

According to ICAO (International Civil Aviation Organization) guidelines:

• The ARP should be located near the geometric center of the aerodrome.
• Once established, it typically remains fixed, even if the airport expands.
• Its coordinates are published in the Aeronautical Information Publication (AIP) for navigation and planning purposes.

 

[GaryGB]

As my answer is intended to be specific to the SDK XML string cited, it is good to know we must not confuse them with other strings.

Do you have a reference within the Prepar3D BGLComp.xsd file by line numbr(s) ...for the above string(s) sought by the OP ?

GaryGB