What is a VTK File?

What is a VTK File?

A VTK file is a binary file format that we use to log data on your ProStart or SpeedPuck.

When we were developing the data logging for the new ProStart and SpeedPuck, our initial plan was to log the data as GPX files (a universal standard for GPS data). The ProStart logs magnetic heading, heel, pitch, COG and SOG at 4Hz (four times a second). The SpeedPuck logs GPS data at 4Hz. At this sampling rate the GPX files ended up being so large that they were difficult to work with.

After consulting with the developers of ChartedSails and Sail Njord (leading GPS replay and analytics apps), we decided to work with them to develop a much more compact, open binary format called the VTK Protocol.

VTK Protocol is fast to write and the files are compact and highly portable. Complete documentation for the VTK Protocol and some sample code for parsing it are here:


VTK files can be imported directly into ChartedSails and Sail Njord.

If you are not using either of those applications, our friends at ChartedSails have also created a permanently free utility (no sign up required and the data doesn’t leave your computer) which converts VTK to GPX or CSV:


GPX works for Expedition, RaceQs, GPS Action Replay (free and Pro), and other GPX viewers. CSV works for Excel, Google Sheets or Tableau. In GPX or CSV format the data from your Velocitek device stays at 4 Hz.