<div dir="ltr">Thanks for the link, Kristian.<div><br></div><div><div>It seemed to me that the source code (specifically proj_etmerc.c:338 - 354) looked like it would calculate the zone if one wasn't supplied (although it also doesn't handle the 'exception' cases mentioned in your link), though I was surprised when I could not find a way to request conversion without specifying a zone.</div><div><br></div><div>As I understand your statement though, there is no way to do this with the current implementation of PROJ tools. </div><div>On the subject of 'correctness', doesn't using a 'clever shell script' like you suggest amount to doing what I was requesting, just doing it outside the PROJ framework?<br><div><br></div><div>Regards,</div></div><div>Robb.</div></div></div><br><div class="gmail_quote"><div dir="ltr">On Mon, Oct 29, 2018 at 1:07 PM Kristian Evers <<a href="mailto:kreve@sdfe.dk">kreve@sdfe.dk</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div style="word-wrap:break-word;line-break:after-white-space">
Robb,
<div><br>
</div>
<div>/Kristian<br>
<div><br>
</div>
<div>
<div>
<blockquote type="cite">
<div>On 29 Oct 2018, at 17:30, Robb Main <<a href="mailto:rmain.mws@gmail.com" target="_blank">rmain.mws@gmail.com</a>> wrote:</div>
<br class="m_6088843805229460402Apple-interchange-newline">
<div>
<div dir="ltr">When converting many lat,long coordinates to UTM, is there some way to setup cs2cs to calculate the UTM zone based on the longitude of the source cordinate system, rather than having to specify the zone on the command line?</div>
</div>
</blockquote>
<div><br>
</div>
No. You can probably do something clever in a shell script if you want, but it is not possible with any PROJ tool. See [0] for an overview of how to determine the nearest UTM zone of a coordinate.</div>
<div><br>
<blockquote type="cite">
<div>
<div dir="ltr">
<div><br>
</div>
<div>What I'm looking for is something like: instead of this:</div>
<div> cs2cs +proj=latlong +data=NAD83 +to +proj=utm +zone=10 +datum=NAD27 ./input.data</div>
<div>you could instead specify:</div>
<div>
<div> cs2cs +proj=latlong +data=NAD83 +to +proj=utm +zone=auto +datum=NAD27 ./input.data</div>
where 'zone=auto' might tell the algorithm to figure the zone out based on longitude of the input coordinate. This would ensure the output data would be correct, even if the input data file contains coordinates that span multiple UTM zones.</div>
</div>
</div>
</blockquote>
<div><br>
</div>
<div>
<div>What you call correct, I regard as potentially incompatible coordinates. What you are proposing here is fundamentally breaking the promise that you are given by the cs2cs application: cs2cs transform coordinates from one coordinate reference system
to another. With your proposed auto-zoned UTM the output crs would not be properly defined and your output coordinates would be incompatible in the case that they span several UTM zones. You are much better of just sticking to one zone - cs2cs will deliver
numerically stable coordinates several thousands of kilometers outside the chosen zone.</div>
<div><br>
</div>
<div>/Kristian</div>
<div><br>
</div>
<div>[0] <a href="https://stackoverflow.com/questions/9186496/determining-utm-zone-to-convert-from-longitude-latitude" target="_blank">https://stackoverflow.com/questions/9186496/determining-utm-zone-to-convert-from-longitude-latitude</a> </div>
</div>
<br>
<blockquote type="cite">
<div>_______________________________________________<br>
Proj mailing list<br>
<a href="mailto:Proj@lists.maptools.org" target="_blank">Proj@lists.maptools.org</a><br>
<a href="http://lists.maptools.org/mailman/listinfo/proj" target="_blank">http://lists.maptools.org/mailman/listinfo/proj</a></div>
</blockquote>
</div>
<br>
</div>
</div>
</div>
_______________________________________________<br>
Proj mailing list<br>
<a href="mailto:Proj@lists.maptools.org" target="_blank">Proj@lists.maptools.org</a><br>
<a href="http://lists.maptools.org/mailman/listinfo/proj" rel="noreferrer" target="_blank">http://lists.maptools.org/mailman/listinfo/proj</a></blockquote></div>