[R-sig-Geo] Did I correctly convert my data from UTM zone 12 to 11?

[Michael Sumner]

You should treat the different sets of coordinates (from Zone 11 and Zone
12) completely separately. You cannot have mixed crs (of projected
coordinates) in a dataset. When you plot in R (generally, even with popular
spatial formats) there is no account taken of crs, the graphics doesn't
know that you plot Zone 11 and then (say) add coordinates from Zone 12,
they will be "shifted" as you say.  (There are exceptions to this plotting
rule but apart from ggplot2::coord_sf they are in dusty corners not front
and centre of plotting code in R).

Some level of coordinate hackery (arithmetic shifting) *can work*  in
limited circumstances, but I would highly recommend against that. Separate
your coordinates into two objects, set the source crs appropriately of the
zone for each, transform each to a common crs.

 (UTM is generally a bad idea but comes with a very popular usage culture
which is a shame, there's no single right choice but you always need to put
thought into the overall region of your data, the properties of the
coordinate space that make sense for your work, and whether you will need
smaller or larger regions in the future for related work ... I would advise
a common crs that is *not UTM* but advice there really depends on the
details of your situation).

It's hard to be more specific without details of your flow, e.g. code
examples.

HTH, Mike





On Mon, Aug 7, 2023 at 6:23 AM Jason Edelkind via R-sig-Geo <
r-sig-geo using r-project.org> wrote:

> hello, first time user here and aspiring grad student. I have a set of
> location data that I’ve been trying to import into google earth engine from
> R as a CSV file. The problem is that about half of my data is from utm zone
> 12, and the other half is from utm zone 11. When I import my original data
> into google earth engine, the zone 11 data is shifted over to the right
> because I use utm zone 12 as the crs in R. After some reading into the
> definition of a utm zone, I tried to just subtract 6 from the zone 11
> latitude values after first converting them to a lon/lat format. This
> appears to have worked as on first glance all of the zone 11 points are
> where they should be, however it feels like too easy a fix for me after
> struggling with this for several days. So my question is, is this an
> acceptable way to convert my data, or am I doing something wrong that could
> result in inaccurate location data? Thanks!
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-- 
Michael Sumner
Software and Database Engineer
Australian Antarctic Division
Hobart, Australia
e-mail: mdsumner using gmail.com

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