R help - Jun 2001 - Easting and northing cf. Latitude and longitude

I think I''ve seen this discussed here before but it doesn''t
seem to
appear in the archive.

I am using the map package which so far has been fine for my purposes.
Some people I work with have GPS type data that defines positions as
number of metres not degrees.  I don''t know how much the system
varies, but in New Zealand, they are referred to as Eastings and
Northings.

What I would like to know is how complicated it is to convert between
such data and the normal latitude and longitude that the map package
uses.  I assume various datum points are used for different parts of
the world, and knowing the appropriate one and the definition of a
"northing" and an "easting", the conversion would be
relatively
straight forward.

TIA




-- 
*************************************************************
Patrick Connolly
HortResearch                        Great minds discuss ideas;
Mt Albert                           Average minds discuss events; 
Auckland                            Small minds discuss people.
New Zealand                                                 .... Anon
Ph: +64-9 815 4200 x 7188
*************************************************************


______________________________________________________
The contents of this e-mail are privileged and/or confidential to the
named recipient and are not to be used by any other person and/or
organisation. If you have received this e-mail in error, please notify 
the sender and delete all material pertaining to this e-mail.
______________________________________________________
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at
stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._

On 22-Jun-01 Patrick Connolly wrote:
> I think I''ve seen this discussed here before but it
doesn''t seem to
> appear in the archive.
> 
> I am using the map package which so far has been fine for my purposes.
> Some people I work with have GPS type data that defines positions as
> number of metres not degrees.  I don''t know how much the system
> varies, but in New Zealand, they are referred to as Eastings and
> Northings.
> 
> What I would like to know is how complicated it is to convert between
> such data and the normal latitude and longitude that the map package
> uses.  I assume various datum points are used for different parts of
> the world, and knowing the appropriate one and the definition of a
> "northing" and an "easting", the conversion would be
relatively
> straight forward.
Errr, sort of ... , though to some extent this depends on the
accuracy you seek.

I implemented such a conversion for Lat-Long/Eastings-Northings
years ago, for the UK Ordnance Survey Grid (which uses E & N),
using the method & formulae published by the OS in a little
booklet (program written in C -- nasty-looking piece of work, since
it is basically a transcription of their formulae). I can send you
the C code for this, as an example, if you wish.

For such a method, you will, strictly speaking, need to know,
for your own national mapping agency:

-- the major and minor semi-axes for the reference ellipsoid
-- the Long. & Lat., and E and N, of the "True Origin"
-- the scale factor on the "central meridian"
-- the map projection they use to generate plane maps
   from Lat & Long data, i.e. the "National Projection"

(the reference ellipsoid may also be called the "map datum").
Nowadays, there is also a complication in that "The Meridian"
is no longer what it used to be, being now defined by satellite
data (and allegedly superior through being immune to continental
drift and similar sabotage of reference points rigidly attached
to dry land). So, in fact, there is a choice of meridians, too ...

There is a further complication in that the GPS system actually
used to generate the data you get, may have been set up to use
some other reference system; so you need to find out what this
was. It may then turn out that you do not have access to the
formulae defining the relationship between their Lat & Long
and your E & N, unless you can find out the relationship
netween their Lat & Long and your National Lat & Long.

The National Projection ( [Lat,Long]->[E,N] ) is defined by
a series of formulae which depend on your Nation; in this
direction it is a one-pass operation. The inversion of it
( [E,N]->[Lat,Long] ) involves an iterative solution. You
should be able to find out from your national mapping agency
how their projection is defined.

Good luck!
Ted.

--------------------------------------------------------------------
E-Mail: (Ted Harding) <Ted.Harding at nessie.mcc.ac.uk>
Fax-to-email: +44 (0)870 167 1972
Date: 22-Jun-01                                       Time: 10:07:14
------------------------------ XFMail ------------------------------
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at
stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._

On Fri, 22 Jun 2001, Patrick Connolly wrote:
> I think I''ve seen this discussed here before but it
doesn''t seem to
> appear in the archive.
In r-help, 20 April 2001.
> 
> I am using the map package which so far has been fine for my purposes.
> Some people I work with have GPS type data that defines positions as
> number of metres not degrees.  I don''t know how much the system
> varies, but in New Zealand, they are referred to as Eastings and
> Northings.
> 
The answer I gave then - there were others - see the archives - was:

One good source is http://www.remotesensing.org/proj/ for the PROJ.4
software. Another is the mapproject program in GMT at
http://gmt.soest.hawaii.edu/. These are both external to R, but it seems
likely that PROJ.4 will form part of an R map package at some stage. You
didn''t say which platform you use - both these are native Unix/Linux,
but
at least GMT is available for NT too. While it would be possible to write
R code to do this, both of these sources are well-tried and so more likely
to work as expected.

I feel that roll-your-own is not necessarily a good solution - map
projection is numerically sensitive, especially when dealing with lots of
significant digits in decimal degrees. The sources here also assume that
you know about the parameters for your projection - as was already pointed
out.

Roger

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Breiviksveien 40, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 93 93
e-mail: Roger.Bivand at nhh.no
and: Department of Geography and Regional Development, University of
Gdansk, al. Mar. J. Pilsudskiego 46, PL-81 378 Gdynia, Poland.



-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at
stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._

As Ted Harding suggested in an earlier reply, the conversions can be
complicated.  Most GPS units provide both geodetic coordinates (latitude,
longitude) and coordinates in the Universal Transverse Mercator projection
(northings and eastings in meters).  See the r-help thread on "map
projections" between 20 April and 23 April 2001.  Also see public domain
software available at http://mapping.usgs.gov/www/html/cartsoft.html.  For
background on map projections try a web search, e.g.
http://www.colorado.edu/geography/gcraft/notes/mapproj/mapproj_f.html.

Denis White
   US EPA, 200 SW 35th St, Corvallis, Oregon, 97333 USA
   voice: 541.754.4476, email: white.denis at epa.gov
   web: www.epa.gov/wed/pages/staff/white/




                    Patrick Connolly
                    <P.Connolly at hortresea        To:     r-help at
stat.math.ethz.ch
                    rch.co.nz>                   (R-help)
                    Sent by:                     cc:
                    owner-r-help at stat.mat        Subject:     [R] Easting and
northing
                    h.ethz.ch                    cf. Latitude and longitude


                    06/21/2001 21:47
                    Please respond to
                    Patrick Connolly






I think I''ve seen this discussed here before but it doesn''t
seem to
appear in the archive.

I am using the map package which so far has been fine for my purposes.
Some people I work with have GPS type data that defines positions as
number of metres not degrees.  I don''t know how much the system
varies, but in New Zealand, they are referred to as Eastings and
Northings.

What I would like to know is how complicated it is to convert between
such data and the normal latitude and longitude that the map package
uses.  I assume various datum points are used for different parts of
the world, and knowing the appropriate one and the definition of a
"northing" and an "easting", the conversion would be
relatively
straight forward.

TIA




--
*************************************************************
Patrick Connolly
HortResearch                        Great minds discuss ideas;
Mt Albert                           Average minds discuss events;
Auckland                            Small minds discuss people.
New Zealand                                                 .... Anon
Ph: +64-9 815 4200 x 7188
*************************************************************


______________________________________________________
The contents of this e-mail are privileged and/or confidential to the
named recipient and are not to be used by any other person and/or
organisation. If you have received this e-mail in error, please notify
the sender and delete all material pertaining to this e-mail.
______________________________________________________
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.
-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at
stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._.
_._._




-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at
stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._

I don''t know whether this will help or not, but some time ago I had to
implement a routine to determine the "great circle" distance between
two
geographical coordinates using the Haversine formula.  I realise that
this is the opposite of what you want, but it might be possible to work
out how to reverse the formula.  The relevant details are at:

http://www.census.gov/cgi-bin/geo/gisfaq?Q5.1

or at least were when I programmed the solution.

Jim


-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at
stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._