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

Mon Aug 7 12:21:04 CEST 2023

 I strongly agree with Michael Sumner. Mathematical adjustments may work but are heavily discouraged. The right way to work is to create two different spatial objects (I recommend to use the vect function of terra package) and then to reproject one of them in the other reference system or both in a common projection as for example EPSG:4326 or something like that. After that you can merge the two spatial objects in a single one or extract the new spatial coordinates to rewrite a new .csv file to be used outside R

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Maurizio Marchi,
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Researcher
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https://scholar.google.com/citations?user=_2X6fu8AAAAJ&hl=en

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Il giorno 7 ago 2023, alle ore 12:02, r-sig-geo-request using r-project.org ha scritto:

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Today's Topics:

  1. Did I correctly convert my data from UTM zone 12 to 11?
     (Jason Edelkind)
  2. Re:  Did I correctly convert my data from UTM zone 12 to 11?
     (Michael Sumner)

----------------------------------------------------------------------

Message: 1
Date: Sun, 6 Aug 2023 15:23:08 -0500
From: Jason Edelkind <jasonedelkind using aol.com>
To: r-sig-geo using r-project.org
Subject: [R-sig-Geo] Did I correctly convert my data from UTM zone 12
   to 11?
Message-ID: <00383000-0C7B-47B4-AB3B-9A2DFAFA92E9 using aol.com>
Content-Type: text/plain; charset="utf-8"

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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Message: 2
Date: Mon, 7 Aug 2023 09:26:32 +1000
From: Michael Sumner <mdsumner using gmail.com>
To: Jason Edelkind <jasonedelkind using aol.com>
Cc: r-sig-geo using r-project.org
Subject: Re: [R-sig-Geo]  Did I correctly convert my data from UTM
   zone 12 to 11?
Message-ID:
   <CAAcGz99UCV1AwYMhg3Km+sa0nL-Ccjg5Bogaizr2YCuuWHjeyw using mail.gmail.com>
Content-Type: text/plain; charset="utf-8"

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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