Thread below got too complex and personal. Rephrased a different way for simplification, here goes--Two examples. This ought to be a test question on the national exam.
- John Doe is in the flat lands of Florida, at elevation 80 feet NAVD.
- He sets his RTK GPS system in to the Florida State Plane projection of the location he is surveying, and he sets his base up and simply uses an autonomous position for the base (one minute observation prior to base transmitting corrections).
- He is about a mile southwest of the northeastern corner of the state plane zone, about as far from the origin as he can get.
- He shoots two RTK points and the state plane inverse on his data Carlson or Survey Pro TDS data collector between these two points shows 1000.00 feet.
- Assume his equipment is perfectly adjusted, and the range pole was perfectly vertical, and no offset error, and that it can survey RTK to the nearest 0.0001 ft (ludicrous, but assume it).
- He pulls out his total station and measures the line between the two RTK points. Assume same perfect instrument condition and rod vertical.
- Can he expect that his inverse on data collector show that his GPS and Total Station measurements of distance will match within 1:10,000?
He does the same thing for two points that are 100 feet apart. Assuming no instrumental or personal error--all instruments and all are perfect. YES or NO.
(I would imagine that this question answers one of the arguments for not using one's real name for identification..hahaahaha.)
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God, forgive me, for I have sinned. Frank wanted only "yes" or "no" for an answer. But, you see, God, I knew that would be impossible for this collection of participants. Mine will only be the first in a long list of long-winded answers that don't really say "yes" or "no".
My procedure, I'm not sure what the results in Florida would be, is to get a scale factor out of the data collector. If I use this scale factor, my total station distance will match the GPS inverse pretty close.
One statement I saw in the thread below was that at the central meridan of a projection the scale factor is 1. Maybe I misread the statement but I don't think that is correct. In Illinois I'm not to far from the far west edge of Illinois and the further west I go the closer the scale factor gets to one.
state plane dist 1000.00, ground dist 1000.03, so yes 1:10,000.
central mont at low elevation state plane dist 1000.00', ground dist 1000.70', so mileage will vary.
Purpose for state plane coordinates in the first place.
Frank Willis, post: 411854, member: 472 wrote:
- John Doe is in the flat lands of Florida, at elevation 80 feet NAVD.
- He sets his RTK GPS system in to the Florida State Plane projection of the location he is surveying, and he sets his base up and simply uses an autonomous position for the base (one minute observation prior to base transmitting corrections).
- Can he expect that his inverse on data collector show that his GPS and Total Station measurements of distance will match within 1:10,000?
He can expect a perfect match. Because the data collector being set to the SP zone will handle the scaling/projection mathematics.
If he used a local/no projection setting in his dc for the TS portion of the work and measured with the TS between the RTK'd points (or, if he measured the distance with a perfectly handled and corrected tape) and he should expect a distance that matched within 1:10000.
All DC's should be able to handle a state plane job, of course the actual distance measured needs to be reduced from ground to grid just like always, no one should actually be doing any state plane work with ground distances mixed with state plane coordinates.
Large coordinate zones with higher elevations will make the difference more acute.
Frank Willis, post: 411887, member: 472 wrote: Purpose for state plane coordinates in the first place.
To have a projection that does not exceed 1:10,000, however this does not include the elevation factor. If your close to 0 elevation which I assume you are. The answer is yes
The problem with an autonomous observation is that the elevation could be off by 100 feet. You would be much better off to start with an ortho elevation taken from a quad sheet. Secondly at low elevation and well distant of the central meridian it is easy to get the scale factor wrong from a plus minus factor. Working near to the ellipsoid elevation is the most confusing of observations. You need a lot more than minimal experience to be sure you are correctly applying factors.
Next your Florida example is not really a problem. Florida has 3 SPC zones, North, East & West. Your example places you at the Northeast corner of Nassau County but you are in fact West of the Florida East SPC Zone Central Meridian and not very far away at that.
http://www.fdot.gov/geospatial/maps/zones_districts.pdf
The most NE corner of the other two zones are also nearer to the Central meridian than points not near the extreme.
Paul in PA
Now Paul, how much "off" an autonamous base solution is, varies by a considerable margin.
More modern units, with fresh software-firmware, should be way better than 100 ft.
My Javad is usually within 3 ft horiz, and 6 ft vert.
( it's cutting edge gear, i know) But, I don't have anything to compare it to....
Nate The Surveyor, post: 412182, member: 291 wrote: More modern units, with fresh software-firmware, should be way better than 100 ft.
My Javad is usually within 3 ft horiz, and 6 ft vert.
I agree
I used an autonomous position in two different locations and had similar results with my Topcon Hiper Lite+ unit. Also a few days ago I printed a page with coordinates for control I might need to locate some utilities, but forgot the sheet after receiving several calls on my way out the door. I ended up using another autonomous position with the X91+ unit I recently purchased and came up with a couple of feet horizontal and three feet vertical. I believe it was set to average 10 positions.
Frank Willis, post: 411854, member: 472 wrote:
- John Doe is in the flat lands of Florida, at elevation 80 feet NAVD.
- He sets his RTK GPS system in to the Florida State Plane projection of the location he is surveying, and he sets his base up and simply uses an autonomous position for the base (one minute observation prior to base transmitting corrections).
- He is about a mile southwest of the northeastern corner of the state plane zone, about as far from the origin as he can get.
- He shoots two RTK points and the state plane inverse on his data Carlson or Survey Pro TDS data collector between these two points shows 1000.00 feet.
- Assume his equipment is perfectly adjusted, and the range pole was perfectly vertical, and no offset error, and that it can survey RTK to the nearest 0.0001 ft (ludicrous, but assume it).
- He pulls out his total station and measures the line between the two RTK points. Assume same perfect instrument condition and rod vertical.
- Can he expect that his inverse on data collector show that his GPS and Total Station measurements of distance will match within 1:10,000?
He does the same thing for two points that are 100 feet apart. Assuming no instrumental or personal error--all instruments and all are perfect. YES or NO.
There's a lot of missing information here regarding exactly how the data was captured, but I think the heart of the question is a really complicated way of asking if a grid distance is equal to a ground distance. And that answer is obviously no, the grid distance and ground distance between two points will never be the same. It doesn't matter if you are measuring 1' or 10,000', assuming we could measure to an infinite level of precision, the grid and ground distances would be different.
As to whether it will be within 1/10,000, it sort of seems silly to calculate as that's it implies the difference between grid distances and ground distances is error. They are different pieces of information and just because they are both 'distances', you wouldn't directly compare them, certainly not calculate an error between them. If you wanted to compare, you'd first need to adjust one to match the other with a scale factor, then you could determine the difference or error.
All that said, I'm just a lowly student and might be in over my head, but that's my interpretation of the question.
Nate The Surveyor, post: 412182, member: 291 wrote: Now Paul, how much "off" an autonamous base solution is, varies by a considerable margin.
More modern units, with fresh software-firmware, should be way better than 100 ft.
My Javad is usually within 3 ft horiz, and 6 ft vert.
( it's cutting edge gear, i know) But, I don't have anything to compare it to....
Compare to our gear. I have used leica 500, Trimble R8(?), leica 1200 and leica Gs16 and i don't ever recall seeing a navigated position off anything like 100'. And I've hit the 'HERE' key more than a few times. I'm certain 15' is all I ever see since the leica system 500 days, and if I saw 30' I would be trying to figure out why
Paul is using some old ashtech gear. It might be out of date by 20 years...
No way would the height be off by 30 m. I think he is referring to using ortho heights instead of ellipsoidal heights (common error).
OK, I have been outed. That 100' comes from when I first started with L1 only.
To tell the truth I have not compared a raw to a post processed position in years since my current methodology is to get an OPUS-S solution as soon as I download my first receiver. I download my other receivers with some OPUS-RS occupations. I then grab the newest ephemeris I can off the web and then post process. I may wait for OPUS-RS solutions to compare and possibly readjust, but I have had solutions that I have accepted as "Once and Done".
BTW, my legacy Z-12s have been dedicated to holding my floor down.
Paul in PA
John Hamilton, post: 412226, member: 640 wrote: No way would the height be off by 30 m. I think he is referring to using ortho heights instead of ellipsoidal heights (common error).
Thread Hijack -
John,
It's early, but are you thinking about going to INGEO in Portugal this fall? I may try and combine it with a vacation in Spain. One of my guys has a masters from the Slovak University of Technology, so he knows a lot of the organizers.
James Fleming, post: 412228, member: 136 wrote: Thread Hijack -
John,
It's early, but are you thinking about going to INGEO in Portugal this fall? I may try and combine it with a vacation in Spain. One of my guys has a masters from the Slovak University of Technology, so he knows a lot of the organizers.
Jim: I wrote a reply, thinking you were referring to InterGeo ( http://www.intergeo.de/intergeo-en/ ), now I see that it is INGEO ( http://ingeo2017.lnec.pt/about.html ). I actually know someone (from deformation and FIG conferences) who works for the Portuguese National Laboratory for Civil Engineering. She is probably the main organizer, always very involved.
By the way, InterGEO is a great exhibit, if anyone wants to see a lot of unusual survey products, that is the place to be (those Germans are mighty clever).
The FIG conference is in Helsinki this year at the end of May, but I am going to Ecuador earlier in May (Geodesy junket) , and my family wants me to go to Cancun the same week that FIG is happening (daughter who lives in Mexico's birthday). I have not made a decision yet about Helsinki, but a trip to Portugal (never been there) and Spain (4 times, love it there) sounds better! I will have to take a closer look.
Now that I look at it, ingeo sounds very interesting, right up my alley. I have been to a number of deformation conferences (last one in Vienna last year), this looks like some of those, always looking to learn more. I had submitted a paper (and was accepted) for FIG, but this looks like a more appropriate venue (it is for subsidence monitoring)
L1 is much better than that, the 100' (or more) probably goes back to the days of selective availability (SA). How many remember that? President Clinton turned it off by some decree in 2000, before that you had to be careful using C/A code positions to seed data processing. Positions could be off by 100 meters, not just heights, but usually were not that far off, probably closer to 10 to 20 m. Still enough off to introduce a bias into post processed results. I would always process first, then constrain a station to published values, adjust, and reprocess again using the updated positions (actually, I still do that by habit). In large networks (large in area) it really makes a difference, a few PPM can mean cm or dm.
