My expectation is that the normal default datum is WGS83. But again, you ought to check with your air assets. Their databases ought to be to some standard that the FAA and the manufacturers have agreed upon. (all assuming USA application)

I've had trouble with website visitors not changing their datum and then blaming my coordinates for being wrong. It happens.

unimogbert

My Garmin has WGS 84, no WGS 83. Isn't NAD27 also fairly common in North America?

It seems if you've got crews on the gound using maps, then it is much easier to have everyone using those maps' datum - probably NAD27 on USGS topo maps. If the maps are setup for UTM then that is probably best, otherwise they'll have to use Lat/Long.

It seems much easier for GPS users in the air (or on ground) to convert to whatever datum & coordinate system than for a map user to change.

Just my $0.02.

Ken

BTW, I have sooo much respect for you SAR folks out there. You're heros in my book.

FWIW, i just looked at my maps here and the USGS 7.5m series are with UTM in NAD27 with offset ticks for NAD83 which for SoCal are to the east by about 100m.
Now, the LA sectional chart says at the top "horizontal datum: north american datum of 1983 (equivalent to world geodetic system 1984). Arggg..

this site datum/lat long conversions is pretty slick - you can enter coordinates in one datum and convert to another, lat/long to utm and back, etc... (continental US only, sorry).

There's another site I only have bookmarked at work that gives utm coordinates on either the 1927 or 1983/84 datum (switch back and forth at will) as you move your cursor over 1:24k quad maps or sat. map. I'll try to send that one tomorrow if anyone is interested.


Both can be handy, esp. if say, your crew has collected data on different gps units set to different datums...

Greetings, While I was on active duty and involved in some flight ops, I kept/used USGS Joint Air Ops Charts. These are topographic w/aviation (VFR) info included. I found these extremely useful for overland SAR missions since our AirSta didn't keep anything but VFR and ocean Nav charts on hand. I have made a few special deliveries to AirSta New Orleans and/or Lakefront airport to get these charts into the hands of the Pilots before they left for a SAR mission up north.
These charts have both UTM and Lat/Long ticks and contain considerable detail. I still keep a few of them on hand for backpacking/camping because of the amount of detail (includes dirt roads).
The charted info is USAF Sat derived and may be a few years behind in updates as far as CONUS areas are concerned (we haven't been invaded since 1814) but they are certainly more detailed than anything else you are likely to find and were designed with the purpose you have in mind.
IRT the chart datum to use, I have found that some chart datums are more accurate in some areas versus others. In the Black Sea and much of the Carribbean, the Naval Hydrographic charts have much to be desired, but the British Admiralty charts of the Med (and Black Sea) were on the money IRT the GPS coordinates. NOAA charts were the overall best in U.S. waters and as far out as they were useful (including crossing the N. Atlantic Ocean. Comparison of gps position, known position, and the various datum charted positions will generally tell you which is the best to use in whatever area you are operating in. In CONUS, I find the 1927 datum to be about the overall best when covering a large area in a short amount of time. For a small area, the 1984WGS seems to work best.

And the answer is NO, I did not have the "NORMAL" USCG career path. <img src="/images/graemlins/tongue.gif" alt="" /> <img src="/images/graemlins/grin.gif" alt="" />

http://oregonstate.edu/~reeset/html/scale.html

Measure the distance between gridlines and plug it in to get your map scale.

Here in N. CA we use both NAD84 and 27 depending on the maps.
People lost, tend to be in remote areas that are the last ones
updated by USGS and so we sometimes use the older map data if that is where the search is.

Some planes and copters we have dealt with cannot (or won't)
use UTM. And ground searchers in terrible conditions and dangerous
terrain shouldn't be using mapping methods that slow them down
(Lat/Lon). So we use both. And practice.

We also have use of a communications van which does the math for us.
If we are in a snow storm at night, it can be a bit hard or dangerous to stop
and figure out the other location data, so we simply call the com van with our utm coordinates and they can then speak to the planes using Lat/Lon. We also, of course, give redundant location information (land marks, section corners etc.) The com van will then help us plan a route around avalanche terrain and other obstacles and give us compass bearings etc. even if we can't see where we are going. They also track everyone on
computer and when a team returns they plug in the GPS and download
the route. At least once, we found the missing when the computer map
showed a small hole in our search pattern.

It is nice if your GPS units can quickly toggle back and forth from UTM
to Lat/Lon. We have a lot of older Etrex that take a bit of fiddling to
convert. Since we usually are in hasty teams of 3 or 4, one team member
can leave his GPS unit on Lat/Lon if we need to coordinate directly
with the planes and copters.

There is an advantage to just being able to read 6 numbers off as to your
location (UTM) when the radios are breaking up.

There is no WGS83 that I am aware of, but there is a NAD83.

Ken, it isn't a map user or a GPS user thing. You can't do SAR work with just a GPS, and you shuoldn't do any land nav without a map. The problems lies when the maps on the ground differ from the GPS in the air or other ground units...