Pid & Designation

[+Team RAGAR]

This has most likley been asked before but.... Here it goes.

 

I understand that the PID is a two letter and four number identifier.

 

How come these PID aren't stamped on the survey disk. The ones I have found are stamped with a letter number combo that is referenced on the page as a "designation".

 

Can anyone explain this maddness to me?

[ArtMan]

It's not madness at all. Just two different systems for referring to the same thing.

 

Think of the DESIGNATION as the name and the PID as a kind of social security number.

 

You may be known as — to make up a name — Charles A. Smith, Chuck Smith, or Chuckie. And there are no doubt plenty of Charles A. Smiths around the country. But you are also 123-45-6789, and there's only one person with that number.

 

Likewise, there may be many marks with designation HALL or M 133 OR BAPTIST CH SPIRE, but only one AA1234

 

Designations pre-date PIDs, I think. And although I am not a surveyor, I believe most working surveyors will more likely refer to a mark by its designation, rather than its PID.

 

-ArtMan-

 

[edited to fix a typo]

Edited April 28, 2006 by ArtMan

[+Kewaneh & Shark]

... I believe most working surveyors will more likely refer to a mark by its designation, rather than its PID.

 

-ArtMan-

 

A designation is usually easier to use than a PID, but the PIDs get used too. Usually during the course of a project, once a particular mark has been identified as the mark to use, it is simply known as 'the Benchmark'. There are also times when we use more endearing (non-technical) terms for a mark, however, most are inapropriate for a family forum such as this.

- Kewaneh

[+Klemmer]

Now THOSE are two of the most direct and useful (and colorful!) answers to a serious question I have ever seen. Nice job, folks.

[+BuckBrooke]

There are two approaches to creating a unified database where a large number of disks have been put down over time by a large number of agencies. You can call a disk/station whatever's stamped on it. Or, you can give everything a different name, regardless of the station.

 

The Canadian version of NGS, the Canadian Spatial Reference System (CSRS), generally uses the inscribed name, or designation, as the Unique Designation. An example is 79C366. If there's no stamping, or that name's already taken, or for whatever other reason, they assign it an ID, often but not always a 6 digit number. An example is 663402. I think the UDs are all 6 digits, but it's a mixture of numbers and letters based on the station. Ostensibly, then, you could get 2.2 billion stations using all possible number & letter combinations (36^6), of which 210,000 are used. Here's a cool map of the vertical stations in the Canadian geodetic network.

This makes it hard to get all the disks in an area, or know where a disk is roughly located based on it's Unique Designation. It does remove most of the confusion of using two names.

 

The NGS assigns each disk a unique two letter, four digit PID. This gives the NGS 6.8 million possible PIDs (26^2*10^4), of which about 720,000 are used. The two letter combinations are assigned geographically, in 1/2 degree North-South by 1 degree East-West chunks. So, you can know roughly where a disk is, and you can distinguish each disk uniquely. But, you have to deal with two names.

Edited April 28, 2006 by BuckBrooke

[+rogbarn]

It's amazing how things come around in a circle sometimes. Read this thread from almost 4 years ago, started by yours truly:

Difference between PID and designation

Edited April 28, 2006 by rogbarn

[+rogbarn]

The NGS assigns each disk a unique two letter, four digit PID. This gives the NGS 6.8 million possible PIDs (26^2*10^4), of which about 720,000 are used. The two letter combinations are assigned geographically, in 1/2 degree North-South by 1 degree East-West chunks. So, you can know roughly where a disk is, and you can distinguish each disk uniquely. But, you have to deal with two names.

 

I can't find the thread(s) but the group did some analysis of PIDs and found that PIDs are assisgned in blocks of 1 deg lat by 2 deg long. I put together the data and posted it as a spreadsheet, someone else overlayed it on a map of the US. The result is pretty neat and is available somewhere. I'm sure some kind soul with a better memory than mine will post the URL.

Edited April 28, 2006 by rogbarn

[mloser]

Zhanna did the map you are thinking of. You can view it at Zhanna's PID map. Be sure to check out the rest of her site too. She has a lot of other benchmarking goodies, including an applet that will let you look up NGS datasheets quickly.

[+BuckBrooke]

Off by x2 is pretty good error for an astronomer. :-)

[+Black Dog Trackers]

In programming, an off-by-one error is called an Obi-wan error.

[andylphoto]

 

Likewise, there may be many marks with designation HALL or M 133 OR BAPTIST CH SPIRE, but only one AA1234

 

 

For a good example of this would be to search for designation "NIAGARA", which you can do from this page. You'll see seven marks with the same designation (along with a number of other variations including this word) in seven different states.