Descriptive Terminology

[+emike]

What is meant by the following phrases found in many Station Descriptions.

 

1.THIS POINT IS INTER-VISIBLE WITH STATION...

Is this a technical reference of some kind or does actually mean you be able to see one point from the other

 

2. THE SITE LOCATION WAS REPORTED AS SUITABLE FOR SATELLITE OBSERVATIONS

What exactly does this mean. Can it actually be observed from a space satellite some how, or is it refering using it as a reference point for other observations.

 

Any help Appreciated

 

EMike

[+Kewaneh & Shark]

'...POINT IS INTER-VISIBLE WITH STATION...'

This phrase is usually found on triangulation station descriptions. Triangulation stations are used by sighting from one station to another set of stations. Think of it like this: any triangulation station is one corner of a triangle. A surveyor would set up one station, we'll call point 'A'. The surveyor would then sight to station 'B' and then to station 'C'. Using a compass or transit, the surveyor would measure the angle between lines AB & AC. In order to make this type of measurement, there had to be a clear line of sight. There are many locations where there are multiple stations within close proximity of another but there may not be a clear line of sight. The phrase '...POINT IS INTER-VISIBLE WITH STATION...' tells you which stations can be seen from the station being occupied.

 

'THE SITE LOCATION WAS REPORTED AS SUITABLE FOR SATELLITE OBSERVATIONS'

This phrase is found on stations where there has been a recent (and reported) high-precision GPS occupation. It means that the station has a clear view of the GPS satellite constellation, unobstructed by trees, mountains, buildings, etc. A station in the bottom of a deep canyon or wooded area may be reported as unsuitable for (GPS) observations.

 

Keep on Caching!

- Kewaneh

[+beejay&esskay]

quote:

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Originally posted by Kewaneh & Shark:

 

'THE SITE LOCATION WAS REPORTED AS SUITABLE FOR SATELLITE OBSERVATIONS'

This phrase is found on stations where there has been a recent (and reported) high-precision GPS occupation. It means that the station has a clear view of the GPS satellite constellation, unobstructed by trees, mountains, buildings, etc. A station in the bottom of a deep canyon or wooded area may be reported as unsuitable for (GPS) observations.

 

Keep on Caching!

- Kewaneh

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Tell me if I'm wrong. When reporting a find on the NGS site, they ask if the location is suitable for satellite observation (yes/no/uncertain). If you answer yes or no, that goes into the NGS record, without any satellite observation being made.

 

(NGS criterion is an unobstructed view of the sky above 15 degrees.)

[+Kewaneh & Shark]

I can't say for certain if you're wrong or not, if that's what you're asking. I don't know if simply clicking yes/no will put a note indicating that on the data sheet. All of the notes I've seen describing the GPS conditions have been in the body of the mark description and not listed elsewhere on the datasheet. I do know that the suggested (to Geocachers) 'Mark Recovery Entry' sheet on the NGS website has not got an option to describe the GPS satellite conditions.

 

It is true that one of the NGS's criteria for a location that is suitable for a GPS observation is an unobstructed view of the sky 15 degrees above the horizon, but it is not the only criteria used to determine if a site is suitable. One of the other (probably unwritten) criteria is the use of a survey-grade GPS receiver by a properly trained individual who understands all of the aspects of GPS measurements. This is part of the reason that the NGS will not accept new coordinates for a benchmark. I would assume that they would use the same logic when they receive a report of conditions for GPS observations.

 

Keep on Caching!

- Kewaneh

[Z15]

Yes, it means its OK for GPS, not necessarily that it has been used for such. I personally submitted hundreds on recovery's with these notes in my job with the M-DOT. It was our goal to visit every NGS station and others we were aware in of our region for this very thing, to document which were or were not suitable for GPS. If says time on future surveys to weed out stations that are no good for GPS surveying.

 

For a site to be suitable for GPS, its needs a clear View of the sky for 360° in all directions and no less the 15° above the horizon. It also should be on stable ground and in a safe place. Anything the hinders the use of a tripod, either adjustable or fixed height (NGS use 3m fixed) should be noted in the description. Such as, "the disk is 1 ft from the edge of a 100 ft cliff falling off the the ocean" etc That way, a surveyor can determine weather he wants to chance it.

 

NOTE-An occasional utility pole, lone tree or some other minor obstruction in the field of view may be OK, but should be noted in the decription.

 

One of our crews had to occupy a Tidal Station on Lake Michigan on a dock in a Limestone Quarry. The FBN station was a USLS cut "+" on a tie down for the big ore boats and was 1 ft from the edge of the breakwater. They had to use a bi-pod, thoroughly supported and monitored for plumb with 2 Wild T2 theodolites setup at 90° to each other. They had to do this for 5.5 hrs at a time for 3 different sessions on 2 different days. NGS insisted that this point had to be occupied.

 

[This message was edited by elcamino on May 02, 2003 at 03:40 PM.]

[DaveD]

Elcamino is correct about NGS accepting the recovery information about stations suitability for GPS. I was on the NGS team that developed the specifications for this program. It was our intention to try and provide the best information possible to the public concerning any stations conditions. The user does not have to be submitting a project to NGS for inclusion in the National Spatial Reference System to have information update. Keep watching the NGS web site. We are currently evaluating the capability of users to provide improved positional information specifically for bench marks that currently only have a scaled coordinate value. These updates will take the form of the user providing either corrected (e.g. DGPS) or uncorrected point position values from GPS. These values will be added to the data sheet to improve recovery information. There will be sufficient metadata to ensure the public knows that these values are not the same as obtained from a more rigorous carrier-phase observations network solution.

[+beejay&esskay]

quote:

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Originally posted by DaveD:

Keep watching the NGS web site. We are currently evaluating the capability of users to provide improved positional information specifically for bench marks that currently only have a scaled coordinate value. These updates will take the form of the user providing either corrected (e.g. DGPS) or uncorrected point position values from GPS. These values will be added to the data sheet to improve recovery information. There will be sufficient metadata to ensure the public knows that these values are not the same as obtained from a more rigorous carrier-phase observations network solution.

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Excellent idea. I hope you'll also tell us here when we should check back.

 

I know my GPS is only good to 20 feet or so, but that's better than the scaled coordinates I've seen.

 

quote:

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I don't know if simply clicking yes/no will put a note indicating that on the data sheet. All of the notes I've seen describing the GPS conditions have been in the body of the mark description and not listed elsewhere on the datasheet. I do know that the suggested (to Geocachers) 'Mark Recovery Entry' sheet on the NGS website has not got an option to describe the GPS satellite conditions.

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The suggested site does have a place to enter whether it is suitable for satellite, but you only see it after you've reported it found.

 

NGS does include that report in a special section near the beginning of the datasheet. (I've seen this for reports I have made.) If NGS wants any extra comments beyond the 15 degree visibility, there should be a place to put the warning on the page that asks about satellite observation.