Merry Christmas and Happy New Year Everyone,
I thought this would be a good topic for those surveyors who love the ancient GPS gear that keeps on ticking. Over the years the GIS specialist of the world have gone through a ton of device and software transitions with a preponderance of workflows designed for GIS?ÿ (ESRI) integration.?ÿ In Alaska and with a strong focus on keeping things simple, the lowly Garmin still finds a place in our backpacks and in our surveyors vest as the cheapest, almost free navigation and simple point,line,poly storage device on the planet.?ÿ Don't let Garmin or GIS listserves get you down with overly complicated mechanisms to display, navigate too coordinates.?ÿ Garmin and the folks at Minnesota DNR have the best suite of tools that can fortify navigation to points found on any website and do it with these main focus points:
1) low power consumption, AA battery power
2)Excellent datum handling between NAD83 and WGS84
3) Ease of data transfer via USB and older serial ports (on older models)
4) Cheap and simple to use with free DNRGPS and GeoSetter
5) Buttons for guys with big hands and gloves?ÿ
6) Accuracy typically at 2 meters (don't believe the hype of 5-10 meters)
Cutting to the chase on cost, a Garmin Map76 - $276 +?ÿ MapSource Topo for maps ($35)?ÿfree DNRGPS and a Pocket Card will set you back under $300.
Nothing in the modern suite of 38 Outdoor Garmin models can hold a candle to long deprecated Garmins like the Garmin 76, Garmin Map76C, Garmin Map76S, Garmin Map76CSx.?ÿ C=color, S = sensors like barometer, X=Sirf Chip .?ÿ The entire 76 line floats, incorporates Tides, Trip Computers and simple waypoint averaging, and track log setups.
As far back as the Garmin GPS 76 (last firmware 2005) the device has WAAS enabled (Do enable WAAS - default is NOT ENABLED).?ÿ Ebay prices are around $276?ÿ.?ÿ Disadvantage of going this far back is the 4-pin cable that requires serial interface with the PC.?ÿ There is also no way to limit screen display on this older model.?ÿ Otherwise a solid device
Stepping through the later models,?ÿGarmin Map76C, Garmin Map76S, Garmin Map76CSx you get increasing capacity including ability to limit screen displays and better compass navigation since you can switch between GPS and Compass navigation when standing still.?ÿ ?ÿNone of these have GLONASS, but are otherwise plenty capable of navigation to the 2 meter accurately handled coordinates you feed using DNRGPS
DNRGPS is free and handles the error you will encounter when assuming you set NAD83 on the Garmin and your getting on-the-fly datum transformation. Your not.?ÿ All Garmins use the Molendensky, 3-parameter transform which assumes NAD83=WGS84. Squeezing out this .9 - 1.4 meter shift is easily handled by DNRGPS which uses the NAD83 and ITRF96 shifter at epoch 1997.0?ÿand exposes these parameters for your convenience.?ÿ DNRGPS doesn't throw away the incoming our outgoing coordinates either, allowing you access to either coordinate in Lat, Long, Xproj, Yproj fields in a multitude of agnostic formats including shapefiles.?ÿ DNRGPS in conjunction with any of the 76 series absorbs?ÿ all data using the Garmin Serial interface requiring a simple DLL to connect to any modern PC (Mac's not supported).?ÿ Excellent support too which includes the long history that I have been lucky enough to be involved with inside the Fire/SAR community.?ÿ Check out the support page here?ÿ?ÿwhich includes handy double-sided pocket cards that travel anywhere and maximize "GIS like" settings you won't find on the Geocaching sites on the internet.?ÿ Supporting fire crews with life-saving navigation was the crux of our training and support which has given way to modern GIS (ESRI) centric workflows, but in the day, we were all about Garmin/DNRGPS workflows that today still clearly supports a surveyor's approach to using a simple device to navigate to a point, find your way out of the woods (using Garmin TRACKBACK) and creating KML,shapefiles,csv,GPX files for non-ESRI solutions.?ÿ No internet and did I say 2 AA batteries?
Can't say enough about the lowly Garmin.?ÿ Pick up a Garmin Map76 model.?ÿ Don't forget to have fun too.?ÿ This is the ideal book if you are teaching kids about all things geospatial.?ÿ I've used dozens of these cool, mathematically challenging techniques exposed in the Fun With GPS book.?ÿ Still on sale at amazon.com for $4.00.?ÿ How cool is that?
Joel (with time on his hands with the shutdown).
2) Excellent datum handling between NAD83 and WGS84
Has Garmin fixed the transform yet??ÿ My 76 does a null transform and tells you NAD83=WGS84.?ÿ That's almost 2 meters of error right there (deprnding where you are in North America) if you give it NAD83 coordinates.
Hi Bill93,
No Garmin that I know of handles the shift on display, including top of the line handhelds (see my review of the 276c released last year). When switching on the Garmin to NAD83 for Garmin display, this does nothing to either the display coordinates OR any storage of a waypoint/track.?ÿ The point I was making in 2) was combined with DNRGPS (recommendation), the transform is handled when you Set Projection (file/set projection) to a NAD83 based coordinate / projection. Then, when downloading you get the NAD83 data using 7 parameters.?ÿ Conversely, when importing a NAD83 coordinate, say off of an NGS datasheet, the same 7-parameter shifter is deployed, but with opposite signage to transform the NAD83 data into WGS84 for upload to the Garmin. This eliminates at the precision of the Garmin, that 2 meter shift.?ÿ You have ideal navigation this way, but only through a software. All Garmins assume all data is in WGS84.
Joel
The GPSMap 400 series chartplotters - of similar vintage to the 76's - can make good bathymetry rigs too. GPS and sonar reading combined.
Garmin Homeport software is a free download and handles the data transfer from unit to PC and vice-versa.
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Another emphasis here deserves attention to datum handling. No Garmin software (Mapsource, BaseCamp, HomePort) offer NAD83-WGS84 shifters in handling data to or from an outside source.?ÿ Garmin's reluctance to include this in either device or software has been an impediment to many of us in GIS (and I suppose surveying community). We have tried numerous times to persuade this giant of a company to accept this fact, they have not done so.?ÿ You have to use an independent software to download and upload from WGS84 and To WGS84 for eliminating this shifting error.?ÿ Many in the industry has ignored this, lending to the 5-10 meter estimated error of these devices.
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Joel
The Garmin GPSMap 60CSx units also will tell me what my constelation looks like much faster than my survey grade GPS units can be initilized and warmed up to begin collecting data and allow me to see what satellites I am not connecting with.
Then, so does my GPS Plus app on my phone and it will filter satellites to my needs.
I the Garmin unit for waypoint collecting of monuments, fence corners and GOTO functions to find the other end of boundaries and to guide me to points picked from Google Earth and other sources.
Best recon tool ever.
