A chart-related question ...

[FullyFlapped]

Hi,

Sorry if I'm asking this in the wrong place, but I suspect I'd get howled at if I asked this in Private Flying, wherein I normally lurk !

Does anyone know what the value is for the Central Meridian, used in the Lambert Conformant Conical projection of the CAA's half mill VFR charts ?

I know this is a bit off the wall, but, believe me, I have a good reason for wanting to know !

Thanks all,

FF

[Spitoon]

If it doesn't say somewhere on the chart - and I seem to recall that it used to but I don't have one here to check - try the maps people at the CAA's Directorate of Airspace Policy.

[Alex Whittingham]

Lamberts don't have a central meridian, they have a parallel of origin and two standard parallels. You can back-calculate the parallel of origin if there is a value printed on the chart as 'n' or the 'constant of the cone' or 'convergency factor'. This is the sine of the latitude of the parallel of origin. For instance, if it says n=0.866 it means sin latitude X = 0.866, therefore latitude X, the parallel of origin = 60º.

Central meridians are present on transverse Mercator charts such as the UK Ordinance Survey. It used to be that the half mill charts were Lamberts and the quarter mill charts transverse Mercators. I'm not sure if that is still the case but it should say on the chart.

[edited for spelling!]

[bookworm]

If you look at the bottom of the chart, just above the scale bars, you'll find the projection. Lambert Conformal Conic with standard parallels 49deg20' and 54deg40' (for S of England chart, anyway).

[andyb79]

If you look at the bottom of the chart, just above the scale bars, you'll find the projection. Lambert Conformal Conic with standard parallels 49deg20' and 54deg40' (for S of England chart, anyway).

its the same on the scottish chart.

it also has 'convergence factor 0-78829, datum wgs-84'.