What is DOP, PDOP, HDOP, VDOP and where can I find this information?

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Dilution of Precision (DOP)

The dilution of precision (DOP) is used for measuring the UNI-GR1’s position precision. DOP values describe the current strength of the satellite configuration (geometry), and the uncertainty of the data that the UNI-GR1 can collect at that moment.

The complete calculation behind DOP values can be complex, but is in general: when the DOP value is lower, the certainty that the position gives will be better. As a rule of thumb, DOP values above 5 result in unacceptable positions for DGNSS and RTK in case high accuracy is needed.

The following table as cited from Wikipedia, explains the values more in-depth. UNI-GR1 users generally find values between 0.5 and 2.

DOP Value Rating Description
1 Ideal Highest possible confidence level to be used for applications demanding the highest possible precision at all times.
1-2 Excellent At this confidence level, positional measurements are considered accurate enough to meet all but the most sensitive applications.
2-5 Good Represents a level that marks the minimum appropriate for making accurate decisions. Positional measurements could be used to make reliable in-route navigation suggestions to the user.
5-10 Moderate Positional measurements could be used for calculations, but the fix quality could still be improved. A more open view of the sky is recommended.
10-20 Fair Represents a low confidence level. Positional measurements should be discarded or used only to indicate a very rough estimate of the current location.
>20 Poor At this level, measurements are inaccurate by as much as 300 meters with a 6-meter accurate device (50 DOP × 6 meters) and should be discarded.

There are several different definitions of the dilution of precision. Within the position information of the UNI-Connect’s survey tool, you find the PDOP, HDOP and VDOP values. The different DOP values have various functions in satellite geometry.

Position DOP (PDOP)

This value describes how many satellites are spread evenly throughout the sky. The more the satellites directly above you and the less on the horizon, the lower the PDOP value is.

Horizontal DOP (HDOP)

The effect of the DOP on the horizontal position value. The more good visible satellites low in the sky, the better the HDOP and the horizontal position (Latitude and Longitude) are.

Vertical DOP (VDOP)

The effect of the DOP on the vertical position value. The more good visible satellites low in the sky, the better the VDOP and the vertical position (Altitude) are.

Where can I find these DOP values?

The values can be found in the project environment, where you review your current position information, just like below:

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