Below are snippets from two datasheets, the first representing the L1 phase center of UCD1, the second the ARP of the same CGPS. The first one picked the correct SPC zone (CA 02), the second picked CA 06. What's up with that?
Good question but looking at the scale and convergence I'm gonna guess that 2 is the right one...
EDIT - I just pulled it and got the same result; I'm guessing that someone at NGS fat fingered it when they entered the site info.
> Good question but looking at the scale and convergence I'm gonna guess that 2 is the right one...
Which brings me to a couple questions since I've been messing with OPUS XML raw data.
- What is "convergence"
- What is "point scale"
- "combined factor"
My program doesn't care. I'm extracting that stuff as given but I'm curious what these things are. I probably know what the latter 2 are but their wording has me a little confused.
I appreciate the schooling.
E
> Which brings me to a couple questions since I've been messing with OPUS XML raw data.
>
>
- >
- What is "convergence"
> - What is "point scale"
> - "combined factor"
>
Convergence refers to the angle between grid north and geodetic north at a given point. Combined factor is the product of the grid scale factor and the elevation factor at a given point. I don't know what point scale refers to, though it might be the grid factor at the point.
Pretty sure you're right, Point Scale is grid scale.
> Convergence refers to the angle between grid north and geodetic north at a given point. Combined factor is the product of the grid scale factor and the elevation factor at a given point. I don't know what point scale refers to, though it might be the grid factor at the point.
Thanks guys,
Gees, you all gonna turn me into a geodicist (is that a word) yet.
Now I wish I would have taken notes that day about 10 years ago on a rain day when I asked the resident LS what "Scale factor" was all about when I was putting it into the data collector.
Is there a good book or books I can get on this stuff besides sitting around printing out stuff all day and try to organize it? You ought to see my stack of physics and mathematics stuff.
Actually, I now have a contact at NGS I can ask about the point scale and combined factor business. At least as far as OPUS reports goes anyhow.
E
> What's up with that?
Also a slight difference in the UTM coordinate.
> Is there a good book or books I can get on this stuff ..
GPS for Land Surveyors by Jan van Sickle is the best I know of.
The control point wishes it was in San Diego!
$88 is $88 I don't have. That's at Amazon.
Time I have. Money - nay. Dam! 🙁
The coordinates are slightly different because they are separate solutions. One would think they should be the exact same horizontal coordinate (assuming the APC is directly above the ARP). But, they do not enter any constraints into the processing/adjustment to account for that. So, each position is the result of a different processing run. They may even have used different CORS or epochs.
My opinion has always been that they should NOT publish APC positions, just ARP exactly for this reason. Another (probably more important) reason to not publish the APC is that it will change when they install a new antenna, whereas the ARP will not.
> The control point wishes it was in San Diego!
😀
They always do, until they actually get there.
Thanks Jim!
> $88 is $88 I don't have.
It took me quite a while to find enough empties to redeem before I could buy a copy.
ABEbooks has one for $3.47, free shipping.
It's a clearinghouse for booksellers and prices are usually better than Amazon Marketplace. Note: It is a Canadian company so some credit cards will charge a foreign transaction fee.
Also check Half.com (owned by Ebay).
Melita
Must be a best seller
Free surveying education resources
Someone mentioned that the 13th edition of Elementary Surveying by Ghilani and Wolf is available for free download as a PDF.
Do a search for elementary surveying ghilani 13th edition pdf
It is a good textbook covering the full range of surveying.
Dr Ghilani's web site at PSU-Wilkes Barre has even more useful information and software.
While I have stopped teaching, I have a web site for an introduction to geodetic science class at http:geodesyattamucc.pbworks.com that includes lectures, labs and links for geodesy and related topics. It as developed to support in-class teaching (not correspondence or on-line).
Good luck,
DMM
This issue has been reported to the NGS CORS and database teams. Hopefully it will be resolved shortly. It is curious how this would happen since the NGS datasheet program is suppose to identify the most appropriate SPC zone from the lat/long.