Garmin 301 & 305 Navigation

Hi All,

I thought I would celebrate my 200th blog entry by making a contribution and in light of the recent interest in trail ultras I thought I would offer this up.

Ever wanted to use your Garmin 301 or 305 as a navigation tool? It's pretty simple if you can afford the software and electronic maps on your PC or laptop - but you don't need that stuff - it is a little fiddly - but I believe well worth the effort as a safety precaution if you are running trails at night or on trails that you have never been on before.

The process I'm about to explain might seem a bit complicated at first but if you practice a bit you can get quite efficient at it.

The 301 is fine as is, but if you have a 305 you will need to make sure you have updated the unit operating software to V2.4 from the Garmin website first.

These instructions are for use with 1:25,000 topographical maps using GDA94 map datum in Australia ONLY (more about this later) - the purpose is to assist trail runners be able to program in critical navigation points such as a track junctions so they don't get quite as lost as they otherwise might :-)

NOTE: A GPS should NEVER be used as the primary navigation tool - nothing will ever beat good map to ground navigation and situational awareness - it is however a wonderful tool that compliments good navigation skills.

I'll try not to use jargon but there are a few terms and concepts you do need to know about.

Waypoint: Is any point you would like to include in a route as a critical navigation point e.g. a track junction etc

WGS84, GDA94, AGD66, AGD84: These are different map datums - the only 2 things you need to know is the Garmin uses WGS84 and that Australian maps depending on their age use the other datum types. The good news is that modern Australian maps all use GDA94 and WGS84 and GDA94 are for all practical purposes the same thing. This example shown below only works with GDA94 maps - If you want help with AGD66/84 it can be done I will mention how towards the end. All topographical maps state somewhere what map datum they are based on - a lot of modern maps now have GDA printed boldly on the cover to make life a bit easier.

Universal Transverse Mercator (UTM): UTM is just a fancy term for grid. If you've ever looked at a topo or a UBD for that matter you will be familiar with the grid superimposed on the map. If you have ever done simple map reading - great - because you will understand the concept of Grid References or coordinates - you have a head start ;-)

Eastings: These are the vertical lines of the grid - so called because the numbers at the top and bottom of the map that correspond with these lines get bigger from west to east.

Northings: These are the horizontal lines of the grid - so called because the numbers at the sides of the map that correspond with these lines get bigger from south to north.

Grid Zone: Relates to a particular 100,000 meter square grid that all smaller maps fit into e.g. Blue Mountains 1:25,000 maps belong in Zone 56. You can find this information on the map under "Grid References".

Latitude and Longitude These are points on the earths surface that are measured in degrees, minutes and seconds and these are the units that the garmin displays position in.

Ok then - I have a 1:25,000 GDA94 topographical map and a garmin now what?

Get yourself a ruler and a calculator - but don't fret it aint hard.

Find the "waypoint" on the map you want to program into your garmin.

For the purposes of demonstration I will use a point on the "Mt Wilson" 1:25,000 topo - let's make it the junction of the Great Western Highway and Victoria Falls Road (See point 1. on the map)

View a copy of the map here Hint - if you click on the image you should then be able to click on an icon that appears to restore the image to regular size.

First, you need to establish the Easting coordinate - look at the vertical lines you will note each one has a two digit number at the top and bottom of the map but some are preceded by a smaller font number - you NEED this smaller number (See point 2 on the map). In this case it is the number 2 - write it down.

Then look at the vertical line immediately to the left of the feature you are plotting - in this case it is 46 (see point 3 on the map)- write this down so now you should have 246.

Using your ruler measure off how far it is to the feature from the vertical line in millimeters and multiply the number of millimeters by 2.5 - you MUST get a 2 digit number so in this case where the answer is 7 (ignore the decimal for now) you need to express it as 07 - write these numbers down - you should now have 24607.

Good you almost have your first coordinate 24607 just pop a 0 on the end (or if the multiplication by 2.5 gave you a 0.5 in the answer you can put a 5 there) - you MUST do this for all coordinates you create - so what you need to end up with is 246075 - you MUST, MUST, MUST have 6 numbers. If you haven't got it already this is IMPORTANT!!!

Now you need to repeat the process for the Northing (the horizontal lines) coordinate - the only differences are you work up the map instead of across it, also there will be a 2 digit smaller font number preceding the bigger grid line numbers - in this case 62 (see point 4 on the map)- you need to use both and you also NEED to put another zero on the end (or a 5) of your final number too - the end result is you MUST, MUST, MUST have 7 numbers.

In this case the number you should get is 6279325 (to see where the 79 came from seef point 5 on the map)

Easy peasy - now for the sexy bit.

The sexy bit is plunking it into an excel spreadsheet that will magically convert these numbers from UTM coordinates to latitude & longitude that you can then program into the garmin.

I didn't invent the spreadsheet - the good old Australian Government did - bless em - you can either download a copy or just open and use the spreadsheet by clicking here.

Ok next bit - choose the middle tab - the one that says E,N Zne to Latitude & Longitude

First thing input the ZONE (DO NOT FORGET THIS STEP) - in this case 56 - on this 1:25,000 map it is 56H - don't worry about the alpha character that is just the sheet identifier of this particular map within this particular 100,000 square meter zone and is not required for calculating purposes i.e. just plunk in 56.

Then input the Easting and the Northing coordinates and press enter on your keyboard.

Hey presto - you have a result.

Latitude = -33 degrees, 35 minutes, 44.159 seconds - don't worry about the minus sign that is just indicating that you are south of the equator - garmin deals with this by replacing the minus sign with an S for south.

Longitude = 150 degrees, 15 minutes, 49.13483 seconds

You can do a rough check if this "looks" right - you will notice that in each of the 4 corners of your map the latitude and longitude is printed. Your result should fall within these parameters at about the posi that looks... well yeah, you know, about right - kinda. NB latitude DECREASES as you go up the page whereas longitude increases as you go across the page.

Last thing you need to do is convert the minutes and seconds to minutes with a decimal point (garmin needs it this way - yes inconvenient I know) - now come on you're all runners you know how to do this - just divide the number of seconds by 60 e.g. for the longitude above the seconds are 49.13483 so divide by 60 = 0.819 (garmin will take 3 decimal places) therefore your new longitude is 150 degrees, 15.816 minutes.

Now all you need do is by using the menu on your garmin select Navigation, select Mark Location use the scroll button to take you to the top data field and give your position an identifying name or number so you can recognise it on the list when you want it.

Scroll to position data field and press enter to edit the default latitude and longitude (garmin defaults to current position - or last known position if the GPS is turned off) NB you do not have to put in elevation info as the GPS does not use this to navigate - all done :-)

Now when you want to use the waypoint just use the Find function under Navigation and select the waypoint you want - the garmin will tell you how far as the crow flies you are from the waypoint and what direction you need to travel eg NE (again as the crow flies). You then have the option (if you want) to select the Map or Go To function - I'll leave it to you to experiment for yourself. In Map or Go To the scroll buttons change the scale whilst the mode button changes screens.

Don't be surprised that if in practice the garmin doesn't take you to the exact spot on the ground you want - if it gets within 30 meters you have done darn well - the GPS itself can be up to 20 meters out, using a ruler and the mark 1 eyeball is not the most precise measurement process, number rounding, a little thing called Grid convergence (all your Eastings on your map are exactly parallel but they actually come to a single point at the poles on a globe - wot tha? - it's just too hard to deal with on a flat map so they don't), the fact that man made features LIKE TRACK JUNCTIONS change over time and a host of other variables all introduce errors into the outcome.

The best use of the garmin is that it indicates if you are moving towards or AWAY from the waypoint you are after.

Given that a lot of trail ultras exceed the battery life of a garmin I would suggest just firing it up when you get close to waypoints and use it for guidance and confirmation of your map to ground and/or compass work.

One thing you might notice is that the elevation on your map and the elevation measurement on the garmin are different - apart from GPS inaccuracies (which for elevation can be pretty significant depending on how far apart the satellites that you are locked onto are) - it is also because there is difference in the way that WGS84 and Australian Height Datum (AHD) deal with height (or more specifically sea level)- to make sense of your garmin you will need to subtract 25 meters from the garmin measurement (or vice versa).

If you are a real novice you might want to investigate some more about map reading and how to use a compass. There is a great free publication again provided by the Aussie Government (good to see our taxes being used for good stuff) here

BTW the processes I've described here can be used for any GPS - in fact it is usually easier with bigger GPS units like a Garmin Etrex as they will allow you to enter the Easting and Northing coordinates directly into the GPS without mucking about with conversions. Also - you can read off your current position from the GPS in Easting and Northing coordinates which you can instantly then plot on the map. Unfortunately the 301 & 305 just aren't that sophisticated and why you need to go through the conversion process.

Ok now - if you want to use this process for AGD66/88 here's what you need to do BE WARNED this is an APPROXIMATION ONLY but will get you in the ball park. The difference in position from GDA94 and AGD66/84 is about 200m but this varies a smidgeon from map to map. If you input AGD coordinates into the excel spreadsheet you need to manually correct the result before entering it into your garmin as follows:

Latitude subtract 5.6 seconds (or 0.093 of a minute)
Longitude add 4.2 seconds (or 0.07 of a minute)

Lastly you can use the process I've described in reverse to plot locations you mark whilst on your run for plotting on a map later eg you might want to know exactly where you turned around on an out and back course.

To do this you need to use the Mark Location function on the garmin - your current position will be saved - make sure you remember the number the garmin assigns to the waypoint (or stop and manually edit in a name). When you get home convert the minutes back to minutes and seconds by multiplying the decimal by 60 and then instead of the middle tab on the spreadsheet use the first one.

There now you know what I know - I make no guarantee of the information I have provided - it is up to you to try it and practice it in a safe environment.

There are other sites on the www that offer conversion software - I have chosen this one because it is an Excel spreadsheet that you can download to your PC and because I trust the source.

Also - you can use this process with a UBD too - but you can work out the differences in how to do that for yourself :-p

It took me yonks to work it all out when I first started farting around with GPS units in 2001 - I hope this saves you some time and that you find it useful.

Cheers 2P :-)

PS If anyone spots any inaccuracies or omissions I would be very happy to receive your feedback