Tyler
Member
I was recently working in the field on a topographic survey in a densely covered lot, from the building itself and tree cover. This lot was also very steep. We set up the Triumph 1-M base at the top of the lot on their driveway and it was fairly open overhead which led me to believe it was a good spot for the base. We set another point at the bottom of the lot. This point had about half the sky covered from the building. We let the Triumph LS log data for 2 or 3 hours and then shot it again for about an hour. These points were measured conventionally with a total station too. I have attached the GPS reports:
DPOS REPORT
JAVAD POST-PROCESSING SERVICE
=============================
USER: DATE: 14.09.2018
FILE: 5000 TIME: 21:56:09.171 GPS time
SOFTWARE: DPOS(5/29/2018 9:09:56 AM) START: 2018/09/13 05:29:24.000 PM
EPHEMERIS: brdc STOP: 2018/09/13 09:47:59.000 PM
OBS USED: 7463 / 9246 TIME SPAN: 259 min
ANT NAME: JAVTRIUMPH_1MR NONE Geometry factor: 1.2
ANT HEIGHT: Slant(SHMP) - 1.777 meters FIXED AMB: Yes
ANT DELTA N/E/H: 0.000/0.000/0.000 OVERALL RMS: 0.008 meters
REF FRAME: NAD83(2011)(EPOCH:2010.0000) IGS08 (EPOCH:2018.7000)
X: -2708515.323(m) 0.004(m) -2708516.298(m) 0.004(m)
Y: -4253129.588(m) 0.004(m) -4253128.099(m) 0.004(m)
Z: 3892852.679(m) 0.004(m) 3892852.777(m) 0.004(m)
LAT: N 37 51 20.34711 0.004(m) N 37 51 20.36418 0.004(m)
E LON:E 237 30 35.43359 0.004(m) E 237 30 35.36724 0.004(m)
W LON:W 122 29 24.56641 0.004(m) W 122 29 24.63276 0.004(m)
EL HGT: 75.891(m) 0.004(m) 75.373(m) 0.004(m)
ORTHO HGT: 108.358(m) 0.004(m) [NAVD88 (Computed using GEOID12B)]
UTM COORDINATES STATE PLANE COORDINATES
UTM (Zone 10) SPC (NAD83(2011) /0403 California zone 3)
Northing (Y) [meters] 4189921.964 652313.963
Easting (X) [meters] 10544850.569 1824882.822
Convergence [degrees] 0.31288250 -1.21843795
Point Scale 0.99962478 0.99993084
Combined Factor 0.99961287 0.99991893
US NATIONAL GRID DESIGNATOR: NONE
BASE STATIONS USED
PID DESIGNATION LATITUDE LONGITUDE DISTANCE(m)
NONE CAPO(CORS) N 37 42 51.020 W 122 13 19.445 28360.1
NONE OHLN(CORS) N 38 00 22.498 W 122 16 22.708 25376.9
NONE P181(CORS) N 37 54 52.349 W 122 22 36.267 11927.8
NONE P224(CORS) N 37 51 50.014 W 122 13 08.563 23878.5
NONE TIBB(CORS) N 37 53 27.139 W 122 26 51.317 5414.7
RESIDUALS OF POSITION
VECTOR dX,m dY,m dZ,m dN,m dE,m dU,m
CAPO - 5000 0.003 0.005 -0.008 -0.002 0.000 -0.009
OHLN - 5000 -0.025 -0.001 0.006 -0.004 -0.020 0.015
P181 - 5000 0.010 -0.009 0.015 0.011 0.013 0.011
P224 - 5000 -0.024 -0.010 0.018 0.001 -0.015 0.029
TIBB - 5000 -0.031 -0.008 -0.002 -0.015 -0.022 0.017
****Disregard point 5002****. For 5001 and 5003 very few epochs were gathered, over a short duration, which was likely due to the location of the setup near the tall building. Between the RTK shots (5001 & 5003) on the LS there was 4.3' of horizontal difference and 2.2' of vertical difference. I used the shot with the longer time set to cook which was point 5001.
The RTK data is obviously not accurate but the raw static data that was logging over the long period of time I would think would be more accurate. The horizontal difference between the conventional points and the GPS base and most accurate RTK point (5001) was 6.4' and the vertical difference between point 5001 was 1.1'. With results like this I don't believe I can trust the RTK shot but how do I know that I can trust the Base measurement? I am attempting to convert the total station measurements to NAVD88. Do I need to remeasure shots with GPS or can the base be confidently used?
I had the understanding that if a measurement was taken over a long period of time it would achieve better results but perhaps this is not always the case. I need to know the limitations of the equipment that I am using in order to confidently accept the measurements.
I am still new to using the equipment so any advice on what to do when you are in an environment that is not friendly with GPS surveying is appreciated. Thank you all for taking the time to further my understanding of GPS and its applications using the Javad products.
Tyler Brown
DPOS REPORT
JAVAD POST-PROCESSING SERVICE
=============================
USER: DATE: 14.09.2018
FILE: 5000 TIME: 21:56:09.171 GPS time
SOFTWARE: DPOS(5/29/2018 9:09:56 AM) START: 2018/09/13 05:29:24.000 PM
EPHEMERIS: brdc STOP: 2018/09/13 09:47:59.000 PM
OBS USED: 7463 / 9246 TIME SPAN: 259 min
ANT NAME: JAVTRIUMPH_1MR NONE Geometry factor: 1.2
ANT HEIGHT: Slant(SHMP) - 1.777 meters FIXED AMB: Yes
ANT DELTA N/E/H: 0.000/0.000/0.000 OVERALL RMS: 0.008 meters
REF FRAME: NAD83(2011)(EPOCH:2010.0000) IGS08 (EPOCH:2018.7000)
X: -2708515.323(m) 0.004(m) -2708516.298(m) 0.004(m)
Y: -4253129.588(m) 0.004(m) -4253128.099(m) 0.004(m)
Z: 3892852.679(m) 0.004(m) 3892852.777(m) 0.004(m)
LAT: N 37 51 20.34711 0.004(m) N 37 51 20.36418 0.004(m)
E LON:E 237 30 35.43359 0.004(m) E 237 30 35.36724 0.004(m)
W LON:W 122 29 24.56641 0.004(m) W 122 29 24.63276 0.004(m)
EL HGT: 75.891(m) 0.004(m) 75.373(m) 0.004(m)
ORTHO HGT: 108.358(m) 0.004(m) [NAVD88 (Computed using GEOID12B)]
UTM COORDINATES STATE PLANE COORDINATES
UTM (Zone 10) SPC (NAD83(2011) /0403 California zone 3)
Northing (Y) [meters] 4189921.964 652313.963
Easting (X) [meters] 10544850.569 1824882.822
Convergence [degrees] 0.31288250 -1.21843795
Point Scale 0.99962478 0.99993084
Combined Factor 0.99961287 0.99991893
US NATIONAL GRID DESIGNATOR: NONE
BASE STATIONS USED
PID DESIGNATION LATITUDE LONGITUDE DISTANCE(m)
NONE CAPO(CORS) N 37 42 51.020 W 122 13 19.445 28360.1
NONE OHLN(CORS) N 38 00 22.498 W 122 16 22.708 25376.9
NONE P181(CORS) N 37 54 52.349 W 122 22 36.267 11927.8
NONE P224(CORS) N 37 51 50.014 W 122 13 08.563 23878.5
NONE TIBB(CORS) N 37 53 27.139 W 122 26 51.317 5414.7
RESIDUALS OF POSITION
VECTOR dX,m dY,m dZ,m dN,m dE,m dU,m
CAPO - 5000 0.003 0.005 -0.008 -0.002 0.000 -0.009
OHLN - 5000 -0.025 -0.001 0.006 -0.004 -0.020 0.015
P181 - 5000 0.010 -0.009 0.015 0.011 0.013 0.011
P224 - 5000 -0.024 -0.010 0.018 0.001 -0.015 0.029
TIBB - 5000 -0.031 -0.008 -0.002 -0.015 -0.022 0.017
****Disregard point 5002****. For 5001 and 5003 very few epochs were gathered, over a short duration, which was likely due to the location of the setup near the tall building. Between the RTK shots (5001 & 5003) on the LS there was 4.3' of horizontal difference and 2.2' of vertical difference. I used the shot with the longer time set to cook which was point 5001.
The RTK data is obviously not accurate but the raw static data that was logging over the long period of time I would think would be more accurate. The horizontal difference between the conventional points and the GPS base and most accurate RTK point (5001) was 6.4' and the vertical difference between point 5001 was 1.1'. With results like this I don't believe I can trust the RTK shot but how do I know that I can trust the Base measurement? I am attempting to convert the total station measurements to NAVD88. Do I need to remeasure shots with GPS or can the base be confidently used?
I had the understanding that if a measurement was taken over a long period of time it would achieve better results but perhaps this is not always the case. I need to know the limitations of the equipment that I am using in order to confidently accept the measurements.
I am still new to using the equipment so any advice on what to do when you are in an environment that is not friendly with GPS surveying is appreciated. Thank you all for taking the time to further my understanding of GPS and its applications using the Javad products.
Tyler Brown