Re: Spanish Map

Thanks Miguel

>>The map datum un spain is usually "European 50" Also called ED-50 short
for
>>European Datum 1950. Newer maps may be WGS84.
I bought it last week so maybe it is "newer", but I cannot find anything
printed on it to say whether it is WGS84.

>>The grid is usually specified in UTM coordinates and also sometimes
>>in lat/long ones with Greenwich as origin of coordinates.
There is no grid (other than the numbered squares). It is marked along the
edges with degrees of latitude and longitude (I cannot see any UTM
coordinates). The text on the cover says that degrees are relative to
Greenwich.

>>For this later maps (1:25.000 1:50.000) a grid covering spain has been
>>defined to numerate them For example a 1:50.000 map could have number 137
>>and the four 1:25.000 maps that fit inside would be numerated 137-1 137-2
>>137-3 137-4
So I presume this grid is only useful for discovering which more detailed
maps to buy and there is no way to equate the grid squares to real world
coordinates.

>>As far as i could investigate by "Elipsoide Internacional" they mean
>>(Hayford, 1924). But it is not the map datum.
Understood. I was just wondering whether "Internacional" implied GRS80 -
but it sounds like it doesn't.

In my own mapping software I have implemented three datums which seem to
apply to some parts of Spain as listed below (numbers in brackets are
Helmert parameters TX, TY, TZ, S, RX, RY, RZ)...

Portugal/Spain (EUR D) (84, 107, 120, 0, 0, 0, 0)
Spain except NW (EUR-7) (131, 100.3, 163.4, -9.39, 1.244, 0.02, 1.144)
Spain NW (EUR-7) (178.4, 83.2, 221.3, -21.2, -0.54, 0.532, 0.126)

I got these from ftp://164.214.2.65/pub/gig/datums/NATO_DT.pdf but there's
no guidance as to which datum to use where. For example, where does "NW
Spain" end and "Spain except NW" begin?

Do you think it is likely that the map uses one of these? I am guessing
Spain except NW is the right one.

Regards
Keith









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