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YeOleImposter

... Established By Gps Observation

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I just noticed on SA2222 that the Old Datasheet from GC.com has these lines:

 

SA2222.The horizontal coordinates were established by GPS observations

SA2222.and adjusted by the National Geodetic Survey in May 1991.

 

The Current Datasheet from the NGS has these lines:

 

SA2222.The horizontal coordinates were established by GPS observations

SA2222.and adjusted by the National Geodetic Survey in July 2001.

 

The History shows:

SA2222 HISTORY - Date Condition Report By

SA2222 HISTORY - 1981 MONUMENTED NGS

SA2222 HISTORY - 19810724 GOOD NGS

SA2222 HISTORY - 19890619 GOOD NGS

SA2222 HISTORY - 19901128 GOOD

SA2222 HISTORY - 19920911 GOOD CHANCE

SA2222

 

My Questions:

1) Did someone go out with a GPS in May 1991 and July 2001 to get the coordinates?

 

2) If Yes, Why is it not in the Recovery History?

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This station was not reobserved in 2001, but rather the original 1991 GPS observations were readjusted along with the rest of the GPS work in the state as part of a reobservation of what is called the Washington High Accuracy Reference Network (HARN). NGS maintains all of the original observations for all control points (e.g. angles, distances, astronomic observations and GPS vectors). Occassionally it is necessary to collect these data and perform a reanalysis due to improved measurements. This is a very common practice in geodesy. NGS is currently in the process of readjusting all of the GPS observations in the United States to remove small (1-4 cm) distortions that have crept into the networks over the last 15 years. The changing of positions/elevations due to either improved observational techniques, best instrumentation or tectonic motions is a never ending process.

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The History shows:

SA2222  HISTORY    - Date    Condition        Report By

SA2222  HISTORY    - 1981    MONUMENTED      NGS

SA2222  HISTORY    - 19810724 GOOD            NGS

SA2222  HISTORY    - 19890619 GOOD            NGS

SA2222  HISTORY    - 19901128 GOOD

SA2222  HISTORY    - 19920911 GOOD            CHANCE

SA2222

 

My Questions: 

1) Did someone go out with a GPS in May 1991 and July 2001 to get the coordinates?

 

2) If Yes, Why is it not in the Recovery History?

Looks to me the history is not complete. Compare the GEOCACHE data sheet to the NGS data sheet:

SA2222* NAD 83(1991)-  46 17 59.97813(N)    119 11 39.78437(W)    ADJUSTED
SA2222* NAD 83(1998)-  46 17 59.97966(N)    119 11 39.78522(W)    ADJUSTED 

Something happened in 1998 that is not logged in the history. Goes to show that adjusted can be readjusted, even if by a few mm.

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This station was not reobserved in 2001, but rather the original 1991 GPS observations were readjusted along with the rest of the GPS work in the state as part of a reobservation of what is called the Washington High Accuracy Reference Network (HARN). NGS maintains all of the original observations for all control points (e.g. angles, distances, astronomic observations and GPS vectors). Occassionally it is necessary to collect these data and perform a reanalysis due to improved measurements. This is a very common practice in geodesy. NGS is currently in the process of readjusting all of the GPS observations in the United States to remove small (1-4 cm) distortions that have crept into the networks over the last 15 years. The changing of positions/elevations due to either improved observational techniques, best instrumentation or tectonic motions is a never ending process.

Thanks!

 

So, I am curious, was the 1991 GPS data from the 1990 observation? Is there a way to tell from the datasheet?:

 

SA2222 HISTORY - 19901128 GOOD (Nobody)

 

Surprised no organization was listed as doing the observation and if it was NGS and GPS readings were taken am surprised that the recovery note itself was so sparse:

 

SA2222'RECOVERED 1990

SA2222'RECOVERED IN GOOD CONDITION.

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I'm wondering about the adjustment process. Is it done for the whole country at once? I assume that horizontal control and vertical control are done totally separately, although a few PIDs might occur in both sets.

 

DaveD  Posted on Jul 6 2004, 08:11 PM

the original 1991 GPS observations were readjusted

Does this mean that adjustments are done with only one type of horizontal control to the exclusion of the others - GPS only in one adjustment, Third order stations in another, or do you use weighting for the different order qualities within the adjustment?

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The History shows:

SA2222 HISTORY - Date Condition Report By

SA2222 HISTORY - 1981 MONUMENTED NGS

SA2222 HISTORY - 19810724 GOOD NGS

 

I would say this is when the field work was done for the GPS

SA2222 HISTORY - 19890619 GOOD NGS

 

SA2222 HISTORY - 19901128 GOOD

SA2222 HISTORY - 19920911 GOOD CHANCE

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