GPS by Bob Wheeler

This is a collection of notes that I made while learning to use my Garmin GPSmap 60CS. They should be applicable to any of the GPSmap 60 and 76 devices. They are not “stand alone” notes since I assume that the reader is familiar with the Garmin manuals — the “Owner’s Manual” and the “Mapsource user’s manual and reference guide.” My notes only attempt to clarify those things which I found puzzling.

CONTENTS

[accordionwrap] [accordion title=”Direct and calculated routes”] I’m not sure what my initial mindset was anymore, but a key factor in understanding this stuff is the distinction between “direct routes,” and “calculated routes.” The Garmin manuals use words like “Follow Road,” “Off Road,” “Routable,” and “Non-routable,” to refer to this distinction, and to confuse the novice I suppose. To begin with, a “route” is an ordered sequence of “waypoints, “ and “waypoints” are specific locations on a map given by latitude and longitude coordinates. If “home,” “stop light,” and “store” are waypoints with specific map locations, then a route is [“home”, “stop light”, “store”]. A direct route is a set of straight lines on a map connecting “home” and “store,” while passing through “stop light.” A direct route is shown below: . A calculated route is a path that follows roads which are chosen by a computer program to meet certain criteria: thus a calculated route will go from “home” to “store” and should pass through “stop light,” but the path it takes, involving other roads, is the result of the criteria chosen, the algorithm involved, and the computer on which the program runs. A calculated route is shown below: At first blush, it would seem that a calculated route would always be the best choice, and that a direct route, with its legs cutting across country, like a crow flies, would be of no use. In fact, neither conclusion is correct, and both kinds of route are useful. The difficulty with calculated routes is that they do not always go where one wants them to go, and to add insult to injury, the calculated routes in the MapSource window on a PC, may differ from the calculated routes on the Garmin device. These are after all two different calculations, using similar but different implementations of the algorithms, which are running on different computers. Mostly, the two agree, but they differ frequently enough so that one should verify a downloaded route before using it. For those who are interested, the calculation being done is a “shortest path” calculation. Given a map, and characteristics of the roads connecting locations the problem is to find the shortest path between two locations. “Shortest,” is itself defined as the minimum value of an objective function which is a combination of the values of several criteria, and thus simple distance forms only part of the definition. Highways, for example, may add a large positive quantity to the criterion value if the user has instructed the algorithm to avoid highways. Any optimization algorithm, such as that used by Garmin, is strongly dependent on the starting value. A good guess at the optimum will enable an algorithm to quickly solve the problem; a bad guess, can lead to long computational times and to a solution which may not be optimal. In the present case, the starting value is the set of waypoints chosen by the user. Choose too few, or choose the wrong ones, and the algorithm may produce an unacceptable solution. [/accordion] [/accordionwrap]

Mapsets

Creating and navigating with direct routes

Creating and navigating with calculated routes

Editing routes and via’s

From maps to cue sheets – Cue Sheet Maker

Notes

Direct and calculated routes:                                 I’m not sure what my initial mindset was anymore, but a key factor in understanding this stuff is the distinction between “direct routes,” and “calculated routes.” The Garmin manuals use words like “Follow Road,” “Off Road,” “Routable,” and “Non-routable,” to refer to this distinction, and to confuse the novice I suppose.

To begin with, a “route” is an ordered sequence of “waypoints, “ and “waypoints” are specific locations on a map given by latitude and longitude                                 coordinates. If “home,” “stop light,” and “store” are waypoints with specific map locations, then a route is [“home”, “stop light”, “store”].

A direct route is a set of straight lines on a map connecting “home” and “store,” while passing through “stop light.” A direct route is shown below:

.

A calculated route is a path that follows roads which are chosen by a computer program to meet certain criteria: thus a calculated route will go from “home” to                                  “store” and should pass through “stop light,” but the path it takes, involving other roads, is the result of the criteria chosen, the algorithm involved, and the                                 computer on which the program runs. A calculated route is shown below:

At first blush, it would seem that a calculated route would always be the best choice, and that a direct route, with its legs cutting across country, like a crow                                 flies, would be of no use. In fact, neither conclusion is correct, and both kinds of route are useful.

The difficulty with calculated routes is that they do not always go where one wants them to go, and to add insult to injury, the calculated routes in the                                 MapSource window on a PC, may differ from the calculated routes on the Garmin device. These are after all two different calculations, using similar but different                                 implementations of the algorithms, which are running on different computers. Mostly, the two agree, but they differ frequently enough so that one should verify a downloaded route before using it.

For those who are interested, the calculation being done is a “shortest path” calculation. Given a map, and characteristics of the roads connecting locations                                 the problem is to find the shortest path between two locations. “Shortest,” is itself defined as the minimum value of an objective function which is a combination of                                 the values of several criteria, and thus simple distance forms only part of the definition. Highways, for example, may add a large positive quantity to the                                 criterion value if the user has instructed the algorithm to avoid highways.

Any optimization algorithm, such as that used by Garmin, is strongly dependent on the starting value. A good guess at the optimum will enable an algorithm to                                 quickly solve the problem; a bad guess, can lead to long computational times and to a solution which may not be optimal. In the present case, the starting value is                                 the set of waypoints chosen by the user. Choose too few, or choose the wrong ones, and the algorithm may produce an unacceptable solution.

Mapsets: There are two basic types of mapset: “routable”, and “non-routable.” A non-routable mapset displays roads and other features such as contour lines, but                                 does not contain information that may be used by the Garmin unit to well-calculate routes. It lacks detail about intersections, directions of travel, surface condition,                                 maximum speed, etc. The shortest path algorithm will assume default values for the missing information, with unpredictable results, which are usually of no                                 practical value. There may be some merit in this calculation, but if so, it has escaped me. I would have thought it wiser for the programmers to have                                 prevented the calculation altogether for non-routable mapsets.

A routable mapset contains the necessary information for calculation. If a direct route is desired, this information can be ignored by choosing the “Use Direct                                 Routes” parameter in the MapSet software. (On the Garmin unit, choose “Off Road”.) The extra information will do no harm when constructing a direct route.

Mapsets must usually be purchased, although there are some very good free ones. Most mapsets are non-routable. Garmin sells mapsets called “MapSource                                .” The MapSource United States Topo is a non-routable mapset. The MapSource City Select North America v7 is routable. The best contour maps for                                 bicyclists are to be found in DeLorme’s Topo USA, although the distances are not reliable. An extensive discussion of the various mapsets may be found in                                 Owings, Rich. (2005). GPS Mapping. Ten Mile Press. Fort Bragg, CA. See his website: http://makeyourownmaps.com/GPSmaps.htm.

When calculated routes will be used, It is probably not a good idea to download mapsets from different products since the road locations may be slightly different,                                 and this I suspect, may confuse the algorithm. I imagine that excessive calculation times are a possibility with different mapsets.

One should also use the same product on the PC as on the Garmin device otherwise via’s and waypoints on the downloaded routes may not be quite where                                 they should be. In case of difficulties such as long calculation times, it might be worthwhile to upload the route to MapSource and adjust the via’s and waypoints slightly.

The subsequent discussion is in terms of the MapSource software, and assumes that the same mapset resides on both the PC and on the device.

Creating and navigating with direct routes:

To create a direct route, one marks each turn with a waypoint, and then connects them together into a route. There is no problem in doing this with a non                                -routable mapset, but before creating a direct route with a routable mapset, one should check to see whether or not the “Use direct routes” radio button is                                 checked. Setting this button, tells the software to ignore the extra routing information in the mapset. This button can be found on the Routing tab of the                                 Preferences menu item of the drop down Edit menu — there is no Routing tab for non-routing mapsets, so the problem does not arise.

Using the “waypoint tool” , a waypoint should be created at each turn of the                                 route. For non-routable mapsets, I find it helpful to start each waypoint name with a letter indicating the turn direction, thus I might name a turn “L SouthSt,” or “DL                                 SouthSt,” for “dog leg.” There is a 10 symbol restriction for waypoint names.

Once the waypoints are placed, they may be connected together using the “Route Tool,” . Each of the waypoints should be clicked in route order. I often find it easier, to add waypoints by using the “Route Properties” box, obtained by                                 double clicking the route name on the Route tab. This is because it is sometimes hard to graphically select the correct waypoint when several are close together.

Once the route is created, it may be downloaded to the GPS device. The “Routing” submenu of the “Setup” menu, on the device, should be inspected to                                 make sure it is set up properly. My setup appears as follows:

The “Prompted” entry, in the Guidance Method field, causes a prompt to appear when navigation commences. The Guidance Method choices are “Follow                                     Road,” and “Off Road.” The “Follow road” choice causes the Garmin unit to do a                                     shortest path calculation. “Off Road” means “do no calculation.” Why couldn’t the Garmin manuals have just said that? For direct routes, one can replace the                                      “Prompted” choice with “Off Road” and avoid the prompt when navigation commences. (If the mapset is non-routable, the “Follow Road” choice will produce nonsense.)

To navigate with the route, choose a route from the “Routes” menu, and click                                     the “Navigate” button at the bottom of the screen. Since there is no shortest path to calculate, the route will immediately appear on the map, and one may proceed                                     to follow it. One half mile before each turn, the display will briefly magnify showing the upcoming turn, and then starting 500 feet before the turn it will again magnify                                     and start to count down the distance to the turn. The waypoint name will appear at the top of the screen, together with a compass direction, but “Left” and “Right”                                      information will not be presented; which Is why I prefer to start the names of my waypoints with the letters “L” or “R” or some other indicative letters.

I use two data fields for my map display: “Dist To Next,” and “Time of Day.” The                                      “Dist To Next” field shows a crow’s flight distance to the next waypoint, not the actual road distance; however, as one approaches the waypoint, it becomes                                     more accurate, and I have not felt the loss.

It is possible to create direct routes without using the ”Waypoint Tool.” Clicking on the map with the “Route Tool,” , will create a “via.” A “via” is a sort of “place                                         holder waypoint”: they are in general traversed without special warning while navigating — waypoints are always noticed and signaled during traverse. Via’s                                         take the name of the map feature at that point, and as such their names cannot be changed — forget adding “L” or “R” to them. The Garmin manual sometimes                                         refers to via’s as “waypoints,” and sometimes it uses “via” for waypoint. Routes may be constructed containing nothing but via’s.

Routes and via’s may be edited graphically: click here for more information.

Creating and navigating with calculated routes:

For this one needs a routable mapset, and the “Use Auto-Routing” button on the Routing Tab of the Preferences item on the drop down Edit menu should be                                         checked. My setup is:

The simplest way to create a calculated route is to use the “Route Tool,” . Click on the start of the route, and at various points along it as desired. Press the Esc key when done. The Route Tool may be switched for the Hand tool, , to scroll the map, or the arrow keys may be used. To resume after using the hand                                         tool, reclick the Route Tool. After each click with the Route Tool, a calculation will be done to connect the new leg to the previous route.

If the route is to be downloaded to a GPS unit, one should try to minimize the number of vias used. There is a 50 via limit on calculated routes, plus the GPS                                         device will signal turns better if it is allowed to choose them itself. (When making cue sheets with CueSheetMaker, each turn should be marked with a via, but for a                                         GPS it is best to place the vias well away from turns and use only enough of them to hold the route.)

Sometimes a new leg will take an undesirable path. If so, undo it with the Undo item on the Edit menu, and try again with a shorter leg, thus forbidding the                                         algorithm from straying. If all else fails, one can set an avoidance to prevent a road segment from being used — click the “Manage Route Avoidance” on the                                         Routing Tab shown above. (I have not been able to get these avoidances to work.) The use of route avoidances is not a good idea, however, because they are not                                         transmitted to the device, and the device may calculate a route using the undesirable path.

Routes and via’s may be edited graphically: click here for more information.

There are problems with calculated routes. A calculated route can only follow roads on the device’s maps. If a road is missing from a map, or does not in fact                                         exist, then the calculated route will be in error. Bicycle paths are frequently missing from maps. If the bicycle path is a critical leg then one should use a direct route, not a calculated route.

Some help is available when one encounters a problem on the road, since the device will recalculate a route if the rider strays too far from it. I recently ran into a                                         new highway blocking my route, but after riding 50 yards or so down another road, the device recalculated and showed me a path around the obstacle.The “Follow                                         Road Options” submenu of the “Routing” option on the main menu must be set up properly for this to happen. My page looks like this, where the “Off Route Recalculation” is set to Automatic.:

It is possible to use waypoints created with the Waypoint Tool, ,instead of                                             via’s — use the Route Tool, , to connect them.

To navigate with the route, choose a route from the “Routes” menu, and click                                             the “Navigate” button at the bottom of the screen. If a prompt appears, select “Follow Road,” which will cause a shortest path calculation to begin, as shown by                                             a progress dialog. The calculation should only take a moment or two. Once the calculation is compete the route will be shown on the screen.

There is no half mile warning with a calculated route, but 500 feet from each turn                                            , the display will magnify, and the turn will be shown with text indicating “Left” or “Right.” If the turn is completely computer generated (no waypoint or via), a white                                             arrow will also appear. If the “Auto Zoom” item on the Map Setup is set to ‘On,” the display will shrink to show the entire route when traveling between via’s and                                             then gradually expand as a via is approached. I prefer a more sizable display all the time, so I set this item to “Off,” as shown below:

As previously mentioned, I use two data fields for my map display: “Dist To Next,” and “Time of Day.” The “Dist To Next” field shows the correct on-road distance when using a calculated route.

 

Editing routes and via’s

Routes, via’s, and waypoints may be edited graphically. The “Selection Tool,” , is used for this purpose. When the route is yellow, the Selection Tool selects the route, when it is purple, it selects waypoints and via’s. Clicking or dragging across the route, turns it yellow. Clicking outside the route, turns it purple.

To add a via, click on the route when it is yellow, the Route Tool will appear below the Selection Tool and a black line will stretch from adjacent points on the                                                 route. The Selection Tool may now be moved to a new map point, and clicking it will lay down a new via and add the via to the route. If the Selection Tool is                                                 dragged to a waypoint, the waypoint will be added to the route. Via’s may be moved when the route is yellow by clicking on them: black lines to adjacent via’s                                                 or waypoints will appear and the via may be dragged.

To move a waypoint, the route must be purple. Double click on a waypoint to edit it. Right click on a waypoint to bring up a menu allowing movement or deletion.