Hand-held GPS units typically have a limited amount of memory to store track points. My old Garmin eMap could hold only about 2000 trackpoints, while my newer 60Cx unit can hold up to 10000 trackpoints. There are also sometimes limits on the maximum number of trackpoints in a saved track; for example, the eMap limits the maximum number of trackpoints in a saved track to 250, while the Garmin limits you to 500. But suppose you have a long active track with greater than 500 points, and you’d like to save that track for future use in your GPS? Or you need to get the total number of trackpoints down to fit into your unit’s memory? There’s an easy way to “simplify” the track, reducing the total number of trackpoints without significantly affecting the track shape.
The free version of GPS TrackMaker has a “TrackLog Reducer” function that allows you to simplify a track, eliminating points that aren’t completely necessary to define its basic shape. Start by downloading the track you’re interested in using GPS TrackMaker or EasyGPS, and saving it as .GPX file. Next, load that file into GPS TrackMaker, and use the selection tool to select the track region you want to simplify (for the example below, it’s the entire track):
Now go to Tools => Tracklogs and Routes => Tracklog Reducer. The following window will pop up:
You can choose to reduce the track by resolution, distance interval, create a Route, or by a maximum number of points (“Cut Tracklog if exceeds …”). Clicking on the Preview button will show you how many fewer points you will have in the track using your selected method:
For this example, I’ll use the default of Resolution = 5. Clicking on Reduce will create a new track with a reduced number of points. However, the old track will still be on the screen, and its points will still be selected; use the Delete key to remove those old points. The final track looks like this if the trackpoints are selected:
Very similar in shape, but with only 52 trackpoints instead of the original 321. The blue line is deceptive, though, since it doesn’t correctly follow the simplified trackpoints, and the true track isn’t as good a match to the original as it would lead you to believe. But you can always do another track reduction using a higher-quality setting or different method, until you find one that gives you an acceptable result. Here’s the same track reduced using the distance interval method; more points than the resolution model, but closer to the original track, with about 2/3rds fewer trackpoints:
You can now upload this simplified track directly into your GPS, or save it as a .GPX file for future use.