Who moved the Latitude and Longtitude?

[EGCC Rwy 24]

I'm confused and would appreciate some help from the brains here. For those who don't frequent the "Questions" and "ATC" forums, I have a web site which addresses the topic of reporting points. I have recently added the ability to visualise on a map the area above which each point lies. This is a good example (http://www.nicklocke.co.uk/Points/PointDetail.asp?Point=SPEAR).
My problem is immediately apparent! I would expect SPEAR to be somewhat closer to Southend Pier than SW of Gillingham.

The coordinates are straight from the AIP - 513434N, 0004201E. I suspect that the AIP and the map software are using different "flavours" of Latitute and Longtitude.

Any ideas? If there are different flavours, then a clue on how to convert would be good!

Thanks in advance.

[HugMonster]

Are you using WGS84? Cos that's what most GPS systems use...

Also, you're missing "Abbot" off your list of drinks-related points!

[10W]

WGS84 and the previous system (whose name escapes me, OGB something or other ?) are only likely to give a difference of a few miles at most.

The names of reporting points are not always exactly over the features they are named after. As the aircraft are operating using navigational aids as opposed to visually, the actual location of the waypoint over the ground is of little relevance.

The points are named referring to a central database. This ensures that no similar sounding waypoints exist within a certain radius and that certain letters or combinations which are difficult to pronounce are not used. When an ATC unit wishes to name a waypoint they normally submit several choices which are fed through the database wurlitzer. If it's OK and not in use then that's what will be given. If not, the system will offer up alternatives, which are usually random names with no obvious connection, e.g MATIK, OLKER, TADEX.

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10 West
UK ATC'er
[email protected]

[EGCC Rwy 24]

Hugmonster - the omission has been rectified. I guess it's down to experience - a bad experience with Abbott when I was younger! :-)

10W - thanks for the thoughts, it all seemed to be a little too far away!

I have now cracked it! The AIP appears to show coordinates as decimals eg SPEAR is 513434N 0004201E. In actual fact, these are degrees, minutes and seconds - 51 degrees, 34 minutes and 34 seconds. Converted to decimal with a divide by 60 of the minutes and 3600 for the seconds gives 51.57611 (and so on). An altogether more respectable result when thrown at the map.

Thanks all for your help!!

[Blacksheep]

EGCC Rwy 24,

I just ran those coordinates into UK Streetmap and they come up on the North edge of Southend Airport.

The URL is
http://www.streetmap.co.uk/streetmap.dll?grid2map?X=587087&Y=189868&arrow=Y&zoom=3

(I also posted the URL in a reply to your post in Computers/Internet)

Cheers now and happy navigating...

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Through difficulties to the cinema

[Blacksheep]

And here's a photograph of the navaid...
http://www.streetmap.co.uk/streetmap.dll?grid2map?X=587087&Y=189868&arrow=Y&zoom=1&largeuk=P

You can also see my cousin Whitesheep grazing by the golf course :)

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Through difficulties to the cinema

[reynoldsno1]

An excellent example of the ambiguity that exists between regulatory and technical requirements. ICAO require positions in Lat/Long to be referenced to the WGS 84 geodetic datum in the format DDMMSS/DDDMMSS.
The technical requirement for formatting in RNAV/FME receivers usually uses the format DDMM.MM/DDDMM.MM

You guys be careful now
BTW - the largest difference between WGS84 and local datum co-ordinates is, I believe, in Japan, and it's around 1.8km