GPS Manager User Manual -- Basic Concepts

|  |  | Basic Concepts

## Basic Concepts

Here is a list of a few terms that will be used below.

Waypoints, routes, tracks and laps are examples of data used in GPS receivers.

- a waypoint (sometimes abbreviated to WP) describes a precise location through its geographic coordinates
- a sequence of waypoints is called a route (RT) and is defined by the user
- a track (TR, also called a trail in Lowrance receivers) is a sequence of track points (TPs) recorded by the GPS receiver over a time period and giving the positions, each with a time-stamp, of the receiver during that period, and including if possible the altitude and the depth (both in either metres or feet, depending on the existing option for this)
- a lap (LAP) has a time-stamp for its start, a duration, the total distance, the calories spent, the start and stop positions, and an associated track; a sequence of laps is called a run, and runs are represented in GPSMan by groups that are automatically created when getting laps from the receiver; support for laps in GPSMan exists only for Garmin receivers and must be explicitly selected from the options (receiver parameters) window;

Route stages are the parts of a route between each two consecutive waypoints. Route stages are called edges in Graph Theory, legs in aviation, and links by Garmin. At present, GPSMan deals with three data fields for each stage: a comment, a label (that will appear in the map), and hidden information.

Polylines (LN), also called polygonal lines, are similar to tracks but have points (LPs) without time-stamps. Polylines are mainly used as background in the map window.

Track and polyline segments are subdivisions that, in the case of tracks, normally indicate that there were time gaps in which the receiver got no position information. The representation in the map of a track or polyline having different segments is a polygonal line that is interrupted between each segment (segments with a single point will hardly be visible). Segments are defined by their starting points and in the track or polyline edit window it is possible to mark or unmark each point (except the first) as being a segment starter.

Data items refer to the elements stored in the GPSMan data-base. Apart from the data items the GPS receivers use and polylines, groups (GRs) of such items can be defined and used.

A map background image name can be associated to each data item except for laps and groups, so that when the item is displayed on the map window the named image is automatically loaded if the map is empty. See below for the details.

Forgetting a data item means deleting it permanently from the data-base.

Input/Output operations in GPSMan have the following names (see below for the definitions of the GPSMan file formats):

- loading from and saving to files in GPSMan format;
- getting from and putting into the GPS receiver (this corresponds to the terms downloading and uploading, respectively, used in other software);
- importing from and exporting to files in a foreign format. Currently recognized formats are given below.

Allowed characters in waypoint names of depend on the brand of the receiver. Garmin names can only have uppercase letters and digits, even if Garmin receivers may use others (see the Garmin specification...). GPSMan also accepts lowercase letters if the existing option on this was set by the user, and hyphens. Lowrance names can have uppercase letters, digits, hyphen, single quote, period, parentheses, slash and also space. And there are no constraints on Magellan names. However, if data files are to be shared among users with receivers of different brands, the more strict rules (those of Garmin, at present) should be followed.

When a name with characters not allowed is read from a file or from the receiver, the user is asked for a new name (alternatively GPSMan can generate it, or all names in the current input operation). A name of a waypoint already in the data-base will not be accepted. Cancelling the renaming makes the waypont to be ignored, what may cause inconsistency if it belongs to a route.

Allowed characters in route names also depend on the brand of the receiver. Although some receivers require route names to be numbers, there are others accepting letters and other characters as well.

GPSMan does not check the characters in the route name, but will refuse to output a route with a non-numeric name to a receiver or file if the receiver protocol or the file format disallow it.

When working with Garmin receivers GPSMan will, if the option on this is selected, automatically give numbers to routes with non-numeric names when putting them on the receiver, avoiding numbers already in use for routes and without affecting the data-base. There is a counter for this, initially set to 1 and that can be reset from the receiver window or the receiver menu (`Put->Route->Set counter to 1`).

A unique name is used for each item of each type. When a new item is read in and it has the name of an item of the same type in the data-base the latter is forgotten and overwritten. Exceptions to this are waypoints with the same name and different positions

1. if the renaming option was previously selected by the user.
2. when getting data from a Garmin receiver, if the waypoints were not defined by the user.

in which case automatically generated names will be used for them.

It should be noted that

1. all input operations with the exception just mentioned are destructive: new items will replace data-base items having the same name. This is the behaviour of most GPS receivers, and avoids having obsolete information in the data-base.
2. the test for the equality of waypoint positions may fail because of rounding errors, at least when the comparison implies a change of position format or a change of datum.

Renaming raises the problem of generating a new suitable name for the item. Currently, GPSMan will try to keep the first part of the old name following it by digits. If the constraints on name length and uniqueness cannot be met, the new name will be a two-letter code for the item type and a hyphen followed by a number.

When an item is renamed, its previous name is kept in the remark field.

When generating a name for a new item or for replacing names with unacceptable characters, GPSMan will use a name with a two-letter code for the item type and a hyphen followed by a number, except in the case of routes for which a number will be used.

Renaming waypoints can lead to ambiguities in what are the actual waypoints of routes or groups. This will only happen when reading from a file in GPSMan format having routes with waypoints referred to by name only, or having groups, and in which there are different waypoints under the same name.

To minimise the problems with these situations, GPSMan creates a group containing the items that were renamed and those for which there may be ambiguities, after any input operation in which they occur.

Comments and remarks (NB) can be specified for some items. The difference is that comments can be got from and put into the GPS receiver, while remarks are only kept by the interface and may be saved to and loaded from GPSMan files. The syntax for comments depends on what the receiver accepts. The syntax for remarks is free: any ASCII character, any length, although no blank lines are allowed.

|  |  | Basic Concepts