GPSPrune, a java applet

The project is to build a Linux Mint machine to have the identical functionality and ergonomics as the existing Windows 10 machine. This stage relates to GPS Prune (a Java applet).

Environment & required functionality

GPS Prune (a Java applet) needs to be used on the following machines:

• The Linux Mint Xfce 18.3 laptop "Gandalf";
• The Windows 10 laptop "Legolas".

The synchronisation agent is Google Drive in Windows 10, and grive2 in Linux Mint.

Alternatives

There are no known alternatives to GPS Prune.

GPS Prune's primary objective is, as the website says:

Basically it's a tool to let you play with your GPS data after you get home from your trip.

This is fundamental to the process of recording walking trips.  When a GPS machine is stationery, it cannot accurately log its location, so the raw data contains ludicrous points, which contaminate the data and result in garbage.  GPS machines typically compress the GPS data in real-time, but this comes at a considerable cost: the data required to geotag photographs, for example, is the first causality of such compression.

So the only viable way to use a GPS machine is to take the raw data off the GPS machine, and then have a competent program - like GPS Prune - post-process the data and geotag any photographs.

GPS Prune is written in Java, so needs Java runtime libraries pre-installed on the host machine.

Installation experience

GPS Prune is already a data file (*.jar) in Google Drive, so no further download is required.

Gandalf's non-admin grived the jar file onto Gandalf on the first successful run of grive2.  But although Gandalf can recognise it as a jar file, it cannot yet run the file because it doesn't have the permissions to do so, i.e.

Thunar File Manager > RC > "Open with OpenJDK Java 8 Runtime" > Error (screenshot below):

The executable bit is explained here.  This is all about file permissions, for which an excellent guide about Linux is here.

There is no way of changing the file's permissions in Thunar File Manager (not in Linux Mint Xfce, anyway), so the CLI needs to do it.  The command was one of the following:

Either

chmod u+x "linux modified gpsprune_18.6.jar"

Or

chmod 700 "linux modified gpsprune_18.6.jar"

Because this file originated on Gandalf via grive, the owner is the user who grives.   In this case, it's the non-admin user who ran the CLI command.

The effect of the command was to change the settings from:

-rw------- 1 martin martin 1165767 Jan 21 10:47 linux modified gpsprune_18.6.jar

to:

-rwx------ 1 martin martin 1165767 Jan 21 10:47 linux modified gpsprune_18.6.jar

A Windows user would typically cope with downloading the software, but would not expect to have to change file permissions, even though it makes perfect sense for user to think twice about running an executable on a machine without specific anti-malware software!

User experience

After changing the file's permissions, the applet runs normally.  Linux Mint Xfce 18.3 comes pre-packed with the required Java runtime libraries.

Thunar File Manager > RC > "Open with OpenJDK Java 8 Runtime" > runs!

Although the Windows version of the applet can see related tool exiftool.exe in the same grived directory and therefore can run it, Gandalf is not yet so configured.  There are alternatives methods available to Gandalf to run exiftool.exe, either via Wine or via the installation of exiftool for Linux/Unix (source, source).  The exiftool is essential for saving photographs with metadata, so should be a different blog post.

Conclusion

GPS Prune works normally.  Success.

Completed May 2018.