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180808 Second day of exciting tests for the Swedish cross country team!

Here is a few lines on the second day of tests at Oestersund Stadium, our upcoming World Championship Arena.
So here we are, after Validation Day 2.

Today we tested our cross-country setup: Our GNSS-IMU sensor (this is recording 3D position, 3D speed, 3D acceleration, and 3D angular velocity) is worn on the upper back using a custom-made shirt (see picture below).

GNSS? Complicated? No – more simple than you think!
Well, you got a regular one in your car´s navigation computer, but our differential GNSS can achieve a much higher position accuracy than a regular GNSS. We want to compare its performance against a so-called golden standard or reference system. In our case it was a high-end differential GNSS. This differential GNSS using not only the data sent from satellites but also from one or multiple base stations. The two major downsides are the high costs of such a system, typically in the order of several ten thousand Euros, and the size of the system (think the size of a deep soup plate:-).
To guarantee optimal signal reception the satellite antenna needs to be rather big and should be always oriented horizontally with no trees or mountains obstructing the sky.

In comparison, take our GNSS-IMU sensor which weighs only around 35 grams, costs just above 1000 EUR and also works relatively well in non-ideal conditions. However, the position obtained from that sensor is not accurate to a few centimetres but to about 2-3 meters in ideal conditions and 10-20 metres in medium conditions. Special algorithms are then needed so that we can still do high-level analysis on a professional level where we need a position accuracy of 20 to 50 centimetres.

As a team – we (the Internet of Sports project) meets up to the demands of the ski teams and our other cases, this is also an opportunity for start-ups such as myself to test and build new innovative technique.
My start-up Archinisis is developing such type of special algorithms that are, in this case, optimized to work for cross-country skiing. And today’s measurements will show us how precise these special algorithms are and if/ how we can obtain data good enough for a professional level.

For today we used six athletes who were skiing short loops on the biathlon penalty track and longer loops around the Oestersund Biathlon stadium and out into the forest. A few numbers to summarize our day:
All in all, the athletes skied 39.6 km for us, reaching top speeds of over 50 km/h on some of the downhill parts. At fast speeds in the penalty loops (25 km/h) the athlete feels a centripetal acceleration of approximately 4 m/s2. This means that he feels being pushed out of the track by a force of almost half his body weight!

Tomorrow we will continue with biathlon. Stay tuned again for more insight information and fun facts we discovered during our measurements!