Understanding UTM zones

[sifukd]

Totaly new to Lastools. I'm trying to do a simple reproject using las2las and cannot find decent explantion about the zone syntax in las2las. I'm used to the norm of for instance saying Zone 35S but the "s" in las2las does not exist it seems. Instead there is a T.

Maybe someone can explain how I figure out what the command is for utm zones east of green which.

Thanks

[Martin Isenburg]

Hello,

the letter in the UTM zone string (e.g. the 'N' of '32N') in LAStools are the latitude letters from this UTM grid here:

http://en.wikipedia.org/wiki/Universal_Transverse_Mercator_coordinate_system#/media/File:Utm-zones.jpg 

Hence any letter that is 'N' or higher (e.g. 'O', 'P', 'Q', 'R', 'S', ...) refers to the Northern hemisphere and any letter that is 'M' or lower (e.g. 'L', 'K', 'J', 'H' ...) refers to the Southern hemisphere. Which letter you use does not really matter. You just need to correctly distinguish between Northern ('N' or higher) and Southern ('M' or lower) hemisphere.

All these will re-project the LiDAR points from long/lat to UTM zone 32 in the Northern Hemisphere using the current Datum:

las2las -i in.laz -longlat -target_utm 32N -o out.laz

las2las -i in.laz -longlat -target_utm 32Q -o out.laz
las2las -i in.laz -longlat -target_utm 32S -o out.laz

All these will re-project the LiDAR points from long/lat to UTM zone 32 in the Southern Hemisphere using the current Datum:

las2las -i in.laz -longlat -target_utm 32M -o out.laz

las2las -i in.laz -longlat -target_utm 32J -o out.laz
las2las -i in.laz -longlat -target_utm 32K -o out.laz

Regards,

Martin @rapidlasso

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[Kirk Waters - NOAA Federal]

Look at the UTM map at http://www.dmap.co.uk/utmworld.htm. The letter code is the one running along the Y axis. So, for instance, much of the UK is in zone 30U. It is a little confusing if you're used to using S for south and N for north (since that's all that matters in the equations) and S happens to be in the northern hemisphere.

Kirk Waters, PhD                     | NOAA Office for Coastal Management

Applied Sciences Program      | 2234 South Hobson Ave
843-740-1227                          | Charleston, SC 29405    

coast.noaa.gov/digitalcoast

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[Evon Silvia]

Thanks for clarifying that! I've more than once wondered by "UTM 10S" landed me in the northern hemisphere.

Evon

[Edgar Veldman]

I knew about this for quite a while now, but have had to explain this many, many times to others who were asking the same question.

We could ask Martin to add an additional flag to just differentiate North and South, and not to worry about the individual letter code, something like 'UTM South' and 'UTM North' maybe?

Edgar

[Peter Guth]

I would second that as a good idea.

What is being used now in LASTOOLS is actually the MGRS or USNG zones, which use UTM coordinates but replace some of the numbers with letters.  In addition to the latitude bands, there are two letters used for 100,000 squares (which are not being used here) and special cases for polar stereographic.

Most usages of "UTM" coordinates use the false easting and northing, the 6 degree UTM zone, and just designate the hemisphere (since it affects the false northing used in the southern hemisphere).  See the ESRI or other examples of PRJ files.

Peter L. Guth
Professor, Dept Oceanography, USNA

[Martin Isenburg]

Hello,

as a compromise I have added the possibility to add the northern (or southern) hemisphere via a lower capital 'n' or 's' or 'north' or 'south' to the UTM zone:

D:\LAStools\bin>las2las -i ..\data\fusa.laz -utm 11n -o mist.laz

using projection UTM 'WGS 84 / UTM zone 11N'

D:\LAStools\bin>las2las -i ..\data\fusa.laz -utm 11north -o mist.laz

using projection UTM 'WGS 84 / UTM zone 11N'

D:\LAStools\bin>las2las -i ..\data\fusa.laz -utm 54s -o mist.laz

using projection UTM 'WGS 84 / UTM zone 54S'

D:\LAStools\bin>las2las -i ..\data\fusa.laz -utm 54south -o mist.laz

using projection UTM 'WGS 84 / UTM zone 54S'

Regards,

Martin @rapidlasso