PSRDOP

DOP values for the satellites used in the PSR solution

Platform:

OEM719, OEM729, OEM7500, OEM7600, OEM7700, OEM7720, PwrPak7, CPT7, CPT7700, SMART7, SMART2

The PSRDOP log contains the Dilution Of Precision (DOP) values for the satellites being used in the PSR solution. The PSR DOPs are updated every 60 seconds or whenever the satellites used in the PSR solution changes.

DOP values are a measure of the solution strength. Essentially, the DOPs reflect the geometry of the satellites used in the solution. Solutions with good counts of well-distributed satellites will have low DOPs and should be accurate and reliable. Solutions with fewer or poorly-distributed satellites will have high DOPs and be less accurate and reliable. As a rough guideline, PDOP values less than 4 imply a solution with reasonable geometry.

There can be many reasons for high DOP values. The most common reason is that there are obstructions limiting satellite visibility. Even if satellites are visible and being tracked they might still not be used in the solution if, for example, they are unhealthy or there are not corrections available for them. The PSRSATS log will inform which satellites are being tracked and explain why a tracked satellite is not used in the solution.

The DOPs do not consider that different satellites or signals will be weighted differently in the solution. Therefore, they do not completely reflect the solution quality. Ultimately, the standard deviations reported in the PSRPOS log are the best reflection of the solution accuracy.

 

  1. If a satellite is locked out using the LOCKOUT command, it will still show in the prn list but it will be significantly deweighted in the dop calculation.

  2. The vertical dilution of precision can be calculated by:
    vdop =   √ pdop2 - hdop2

  3. If the DOP is not yet calculated, a default value of 9999.0 is displayed.

Message ID: 174

Log Type: Asynch

Recommended Input:

log psrdopa onchanged

ASCII Example:

#PSRDOPA,USB1,0,50.0,FINESTEERING,2209,511740.000,02000020,1779,16809;1.8150,1.6190,0.8940,1.2150,0.8220,5.0,10,26,2,18,12,5,20,29,31,9,25*982c4334

Field

Field type

  

Format

Binary Bytes

Binary Offset

1

Log header

PSRDOP header

For information about log headers, see ASCII, Abbreviated ASCII or Binary.

 

H

0

2

gdop

Geometric dilution of precision - assumes 3D position and receiver clock offset (all 4 parameters) are unknown

Float

4

H

3

pdop

Position dilution of precision - assumes 3D position is unknown and receiver clock offset is known

Float

4

H+4

4

hdop

Horizontal dilution of precision.

Float

4

H+8

5

htdop

Horizontal position and time dilution of precision.

Float

4

H+12

6

tdop

GPS time dilution of precision – assumes 3D position is known and only the GPS receiver clock offset is unknown

Float

4

H+16

7

cutoff

GPS elevation cut-off angle

Float

4

H+20

8

#PRN

Number of satellites PRNs to follow

Long

4

H+24

9

PRN

PRN of SV PRN tracking, null field until position solution available

Ulong

4

H+28

10...

Next PRN offset = H+28+(#prn x 4)

11

xxxx

32-bit CRC (ASCII and Binary only)

Ulong

4

H+28+
(#prn x 4)

12

[CR][LF]

Sentence terminator (ASCII only)

-

-

-