Measuring GPS (GNSS) Accuracy and Precision

With the recent technological advancements, I’ve recently become interested in RTK GPS and decided it would be fun to compare all the different GPS/GNSS (Global Navigation Satellite System) receivers I own.

I ultimately plan to see how they all compare for both Accuracy and Precision. Although the terms Accuracy and Precision are often used interchangeably, they are in fact very different measurements.

Accuracy is used to measure how “on target” a measurement is, while Precision is used to measure how consistent/close the measurements are.

If you’re a pictures person, here’s a table of images from some of my long range shooting endeavors – It was pleasing to find out I had to photoshop the bottom right image.

My plan is to place each GNSS receiver in the same location, take continuous measurements for 12-24 hours and then graph the results. For the time being I’m unable to measure the accuracy of the receivers as the exact coordinates of the location I am placing them is not yet known.

The location is on top of a solid fence post. The post is ~1900mm above ground level and ~280mm in diameter. Serial data and power is provided from the house over a 40 metre length of outdoor Cat5 cable. All receivers will be tested from the top of this post and their antennas will be placed within 50mm of the middle.

It will be interesting to see the results. First up is the original Garmin eTrex, released to market in 1999.

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