ArcView DRG's across UTM zones ?

ArcView DRG's across UTM zones ?

Post by Elliot » Sat, 11 Nov 2000 04:00:00



I am working on a project that extends from UTM zone 15 to UTM zone 16
that uses DRG maps. I set my projection to UTM-1927 Zone 15 but the last
part of the project uses 3 DRG maps in zone 16.  they appeared way out of
place. I then calculated the EW offset and the NS offset and could get them
in place, however there was a rotation misalignment. I then went and rotated
the zone 16 maps in Corel Draw 3 degrees CW and it almost worked with about
a 25 meter rotation error from top to bottom. I finally fine tuned the whole
thing to work but it took a while.
Anybody know a more straightforward way to accomplish this? Any help would
be appreciated.
 
 
 

1. Plotting data spanning multiple UTM zones

I have 3D data (lat lon depth) over the Gulf of Mex. To plot this data
as a volume with sensical axes labeling I need to convert my data
lat/lon to UTM eastings/northings so its in meters cause my depth is
in meters. Simple, just use Ben Tupper's handy ll_to_utm() to convert
my data lat/lon bounds to meters and then viz passing my xdata ydata
and zdata so's everything's perfect. Problem is my data spans 2 UTM
zones and my conversion is like this

;set data lat/lon bounds, lower left indicated by
lonMinMax[0],latMinMax[0]
lonMinMax = [-90.500000, -84.500000] ;range of longitude
latMinMax = [28.385413, 31.000000] ;range of latitude
utmCoords = ll_to_utm(lonMinMax, latMinMax), ZONE=utmZone)

IDL> print, utmCoords
       744973.76       3142250.3 ;<-easting/northing of
southest/westest pt.
       738705.88       3432086.9 ;<-easting/northing of
northest/eastest pt.
IDL> print, utmZone
          15          16

Hmmm. Data points I passed are in 2 different zones. Notice the false
easting of the southwest point is greater (more east) than that of the
northeast point because, of course, the NE point is closer to its
false origin than the SW point.

I'm kinda new to this UTM stuff, but I did find out that the middle of
each zone is at 500,000. But, I don't think I can just add an offset
of 1,000,000 for each zones easting/northing from the lowest zone
since the zones are not rectilinear, e.g.:

minZone = min(utmZone, max=maxZone)
;add 10^6meters added for every zone's (false) easting from minZone
zoneOffsets = (utmZone[*] - minZone) * (1.0D*10D^6)
eastingMinMax = reform(utmCoords[0,*]) + zoneOffsets
northingMinMax = reform(utmCoords[1,*])
IDL> print, eastingMinMax
       744973.76       1238705.9
IDL> print, northingMinMax
       3142250.3       3432086.9

Plotting this gives a stretched data image. Mult. by 500,000 instead:

zoneOffsets = (utmZone[*] - minZone) * (0.5D*10D^6)

looks alot better, but is a kludge just to make it look good.

So, does anyone know how to do this in IDL?

Danke

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