---------- Forwarded message ----------
Date: Tue, 22 Sep 1998 17:57:48 +0100
From: Darius Bartlett <[log in to unmask]>
To: Maps and Air Photo Systems Forum <[log in to unmask]>
Subject: Re: mean sea level, Alicante (fwd)
At 09:44 22/09/98 -0400, "A. Hausold" <[log in to unmask]> wrote
>To: [log in to unmask]
>Subject: mean sea level, Alicante
>
>Dear members of the list,
>
>I am currently working with a Spanish map and need to take pass points
>inlucding height information out of it.
>
>the map is:
>Mapa Militar de Espana, scale 1:50 000, sheet La Gineta
>
>the height information says that heights refer to "Mean Sea Level in
>Alicante". I need to have heights referring to "Mean Sea Level in
>Amsterdam".
>
>Could anybody please help me with this and provide me with a number for
>the difference between these two levels?
Andrea,
I have no wish to puncture your ideas but, even if such a conversion
formula exists (which I rather doubt), I am rather skeptical about the
merits of such an exercise? You don't state your purpose - presumably you
want to integrate or compare phenomena in Spain and the Netherlands? But
for what?
>From a cartographic perspective, you ask for the "number of the difference
between these two levels" - but difference with respect to what? Which
datum, and which elipsoid, are you using as a baseline for the comparison?
As I see it (I am sure others can correct me if I am wrong), if you are
trying to compare the heights taken from the Spanish map with others
taken from a Dutch map, especially if you are working off comparatively
large scale (1:50,000) maps, then the basic geometry used to construct the
maps will be very critical. I think you will need to check either that both
are based on the same shape of the earth (i.e. same elipsoid), or else that
you take this difference also into account - especially when you are
working off such a comparatively large-scale map.
I will be interested to see what others think...
Darius Bartlett
************************************************************************
Darius Bartlett Darius Bartlett
Department of Geography Roinn na Tireolaiochta
University College Cork Colaste na hOllscoile Corcaigh
Cork, Ireland Corcaigh, Eire
Phone: (+353) 21 902835 Fax: (+353) 21 271980
Mobile: (+353) 86 8238043
E-mail: [log in to unmask] Web URL: http://www.ucc.ie/ucc/depts/geography/djb
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