Many of the sensors near me show a Zero for ‘Position Rating’, but I can not find any more info about what exactly determines the ‘Position Rating’. Can someone elaborate on the exact parameters used to determine this ? What factors is this based upon ?
Position rating provides a measure of how accurate the map position may be.
The position rating is calculated using Google’s Geolocation API. When a sensor connects to WiFi, it sends the IP address to Google for a location estimate. This is then compared against the latitude and longitude set during registration to determine the star rating.
If the sensor is reconnected to a different WiFi network, then the location check will be performed again and updated.
Please note that the 7.03 and 7.04 firmware versions currently have a bug affecting geolocation for some sensors. This is not an issue with Google’s API but rather the firmware of PurpleAir sensors.
If anyone suspects that there is an error in their sensor’s location star rating, please send an email to contact@purpleair.com.
G’day Josh. Any idea roughly how far away the location estimate has to be from the registered location to get zero for position rating?
Greater than 4,000 meters. We’ll publish an article with details on this soon.
Please note that sensors on firmware versions 7.03 and 7.04 have position_rating disabled, so they will automatically show a position_rating of 0. In such a case, it doesn’t necessarily mean that the actual position of the sensor is far away; rather, it is an issue with the latest firmware.
@Facts_Really_Matter @alecgargett
| Distance | Miles (approx.) | Rating |
|---|---|---|
| < 500 meters | (< 0.31 mi) | 5 stars |
| 500 – 800 meters | (0.31 – 0.50 mi) | 4 stars |
| 800 – 1,400 meters | (0.50 – 0.87 mi) | 3 stars |
| 1,400 – 2,000 meters | (0.87 – 1.24 mi) | 2 stars |
| 2,000 – 4,000 meters | (1.24 – 2.49 mi) | 1 star |
| ≥ 4,000 meters | (≥ 2.49 mi) | 0 stars |
Thanks Andrew. It’d be great to be able to filter out by “Minimum position rating”.
If such a feature is introduced, I would recommend setting the minimum to 1 star by default, since there is no limit on how far away a sensor could be if it has zero stars. There’s even a string of zero-star sensors with locations in the Antarctic Ocean that some people have done as a meme.
Great idea, Alec. I’ll certainly add it as a feature request for the developers to look at.