Recording decimal latitude and longitude

[Robert J Raven]

In <199607300852.JAA19046 at mailserver.nhm.ac.uk>, on 07/30/96
   at 09:52 AM, Charles Hussey <cgh at NHM.AC.UK> said:

>>
>>In designing the system I had anticipated that decimal degrees would be
>presented as a positive or negative number with up to four decimal
>places. One of our researchers, who uses a GIS device has alerted me to
>the fact that his GPS device outputs things as degrees and decimal
>minutes (114 24.567'E for example); which would indicate the requirement
>for an integer degree field and a decimal minute field.
>>
>>Can anyone out there who has experience of these things provide details h
>many formats exist for data from GIS/GPS systems and which are the most
>common. >
>
Charles

We have long since solved this problem. GIS units give the results as
degree, minutes and decimal minutes so we all agreed to that standard. We
use a REAL data type and we know that the digits after the second place
are decimalised. We also use a "GIS" program but that requires us to have
decimal degrees. So we have four fields. One each for long and lat as
degree.decimal minutes and one each as computed fields which make the
decimalisation "on the fly". When we dump the points for mapping (e.g. our
Atlas of Frogs, Reptiles, Birds & mammals, Ingram & Raven, 1991) we use
the computed fields. It all happens transparently to the user and there is
no speed loss.

Equally, however, we have a problem with our mapping program which sees
the world as a rectangular card in which the ends are not joined, Fiji on
one side and the other! We wanted to do a map putting Australia at the
centre, straddled by the Indian and Pacific but also with the Atlantic in
one piece. So we rotated one map of the world and moved 0 to Capetown. For
 that we have a second computed field based upon the longitude and we use
that instead of the actual latitude and drop the points onto our
Australia-centred world. It is good for Fiji too because it all stays
together.

We use R:Base in DOS, Windoze and OS/2 implementations and haven't seen
anything that would turn our heads yet.

Rob


Dr Robert J Raven
Museum Scientist, Arachnology
Queensland Museum, Brisbane, Australia

Email: R.Raven at mailbox.uq.edu.au
Home page: http://www.uq.edu.au/~qmrraven