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- Station-velocity-in-post-processing
- 02-08-2011
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I've been using a u-blox EVK-6T with an ANN-MS patch antenna to
collect 24hrs of raw data and then using RTKLIB to post-process it
against a local CORS base station (p478). My understanding is that
this causes my datum to become that of the base station (ITRF00). I'm
fine with that. However, looking at position file for the base
station in question I notice that the epoch given is 1997.0 and that
the base station velocity is also given. This base station wasn't
even established until 2004. So how did they come up with a base
station position with a 1997.0 epoch? Did they subtract 7.0 years of
base station velocity to arrive at that position for that epoch?
Should I be adding 14.1 years worth of base station velocity to
compute a 2011.1 (epoch "now") base station position? That would seem
to make sense, so I have assumed that I should. Otherwise my
positions would also inherit the epoch and could not be adjusted
because I don't know their velocity which could be different.
Note that both the base station and the station I'm occupying in this
case are only 8km apart with no fault lines between them and are both
moving Northwest on the Pacific plate at quite a clip. I'd expect the
difference between taking the base station velocity into account vs.
not taking it into account (14.1 years worth of movement) to be about
0.5m. A standalone (WGS84 epoch "now") solution places me very close
to 2m Northwest of the DGPS (ITRF00 epoch 1997.0) derived solution. I
would have expected them to differ by 0.5m. I thought WGS84 and
ITRF00 were supposed to be within 2cm of each other, so I wonder where
that extra 1.5m is coming from.
I'll soon be receiving a geodetic quality antenna and a dc bias
injector to drive it at the required oddball voltage. Then I hope to
at least be able to collect somewhat higher quality data.
| Antenna Reference Point(ARP): VALLEYCNTRCS2004 CORS
| -------------------------------------------------------
| PID = DG8350
|
| ITRF00 POSITION (EPOCH 1997.0)
| Computed in Mar. 2008 using 811 days of data.
| X = -2430480.710 m latitude = 33 14 08.56591 N
| Y = -4755389.652 m longitude = 117 04 17.70811 W
| Z = 3476057.551 m ellipsoid height = 371.582
m
|
| ITRF00 VELOCITY
| Adapted in Mar. 2008 using 811 days of data.
| VX = -0.0281 m/yr northward = 0.0158 m/yr
| VY = 0.0241 m/yr eastward = -0.0360 m/yr
| VZ = 0.0132 m/yr upward = -0.0000 m/yr
collect 24hrs of raw data and then using RTKLIB to post-process it
against a local CORS base station (p478). My understanding is that
this causes my datum to become that of the base station (ITRF00). I'm
fine with that. However, looking at position file for the base
station in question I notice that the epoch given is 1997.0 and that
the base station velocity is also given. This base station wasn't
even established until 2004. So how did they come up with a base
station position with a 1997.0 epoch? Did they subtract 7.0 years of
base station velocity to arrive at that position for that epoch?
Should I be adding 14.1 years worth of base station velocity to
compute a 2011.1 (epoch "now") base station position? That would seem
to make sense, so I have assumed that I should. Otherwise my
positions would also inherit the epoch and could not be adjusted
because I don't know their velocity which could be different.
Note that both the base station and the station I'm occupying in this
case are only 8km apart with no fault lines between them and are both
moving Northwest on the Pacific plate at quite a clip. I'd expect the
difference between taking the base station velocity into account vs.
not taking it into account (14.1 years worth of movement) to be about
0.5m. A standalone (WGS84 epoch "now") solution places me very close
to 2m Northwest of the DGPS (ITRF00 epoch 1997.0) derived solution. I
would have expected them to differ by 0.5m. I thought WGS84 and
ITRF00 were supposed to be within 2cm of each other, so I wonder where
that extra 1.5m is coming from.
I'll soon be receiving a geodetic quality antenna and a dc bias
injector to drive it at the required oddball voltage. Then I hope to
at least be able to collect somewhat higher quality data.
| Antenna Reference Point(ARP): VALLEYCNTRCS2004 CORS
| -------------------------------------------------------
| PID = DG8350
|
| ITRF00 POSITION (EPOCH 1997.0)
| Computed in Mar. 2008 using 811 days of data.
| X = -2430480.710 m latitude = 33 14 08.56591 N
| Y = -4755389.652 m longitude = 117 04 17.70811 W
| Z = 3476057.551 m ellipsoid height = 371.582
m
|
| ITRF00 VELOCITY
| Adapted in Mar. 2008 using 811 days of data.
| VX = -0.0281 m/yr northward = 0.0158 m/yr
| VY = 0.0241 m/yr eastward = -0.0360 m/yr
| VZ = 0.0132 m/yr upward = -0.0000 m/yr
