[R-sig-Geo] Help with latlong to UTM conversion when UTM zones are different

[Barry Rowlingson]

If you have lat-long data that crosses two UTM zones then its
generally okay to just pick *one* and transform all the points to
that. Use the one that has the most points in. Basically use the UTM
zones as guidelines to pick one UTM zone coordinate system. Unless
your data spans several zones and you want quite high accuracy of
distance measurements. Some points bleeding over into an adjacent zone
are no problem.

All projections are approximations to the earth's spheroid, so points
that are within a single UTM zone have some distortion in their
distance or angle relationships. Transforming points that are within
an adjacent UTM zone is just an extension of that distortion. You can
compute the precise distance error if you want for the furthest points
by comparing with the geodesic distance.

Alternatively you might find there is a coordinate system that spans
your dataset nicely - often when a country or an island or a region
crosses UTM zones there is an official coordinate system defined that
is used by the authorities there.

Also alternatively, there's nothing to stop you defining a transverse
mercator system based on the centre of your data.

Barry



On Fri, Mar 27, 2015 at 7:44 AM, moses selebatso <selebatsom at yahoo.co.uk> wrote:
>  Hello
> I have animal movement data that I have converted from Lat/Long to UTM, unfortunately the data falls in two UTM zones (34S and 35S). For some reason R cannot display both of them in the same window (the 35S data is way off the expected location).
> The question is how do I convert the data such that R can correctly read it?
> Moses SELEBATSO
>
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