Control point

good morning Philos. tell us about the trimble equipment: is it GPS/GNSS? is it total station/EDM? where will the control point be? is there a network of control markers in your project area?

Good morning Moe
My equipment is a GPS/GNSS ( Trimble R6), there is not a network of control point in my working area.

Do you have a pair?

Leap frog and think triangles occupying the 3 pairs of each triangle, then add another triangle and another.

Choose a good primary base and plan your surveys with ties into your local passive control.

Redundancy. Does Trimble have the least square network adjistment? If not, export the vectors to a package that has it (I use Carlson's survnet) and process away.

In my area, I established a 4 point loop with cross ties with setting up the pairs 6 ways for a good 2 to 4 hours. I tied into 2 benchmarks and 2 other points. They were all approximately equidistant. I then started running sub loops to add more points for durations ranging from 30 minutes to 2 hours.

I ran through some major traverses we have with 15 minute occupations using rtk/pp with a base on one major control point, finding, painting and locating almost every traverse point, then changing the base to another control and locating all the points a second time.

Then I started playing with RTK control, but I still prefer static.

Sent from my SM-G930V using Tapatalk

Thanks spledeus,
arround my area there is no benchmark where i can tie my point.
the only benchmark we have it's about 120km distance from the site.

OK, you have a difficult project then. Where is it? How many receivers do you have?

philos, post: 422131, member: 12630 wrote: I am looking for a procedure which can help me to establish news ground control point.

Generally, you probably want to run static vectors from whatever control is available to you new points. Preferably from several known points to your new point, then adjust. Using static procedures you can bring control in from hundreds of miles away.

I do not know if there is data from Continuously Operating Reference Stations (CORS) in your area (we don't know where you are), but there is most everywhere these days. So the thing is to collect receiver raw data on your point for several hours, down load data for the same time period from a number of CORS station surrounding your site, and resolve vectors using a software such as Trimble Business Center (TBC). There are some on-line services (such as OPUS here in the US) which do that automatically, and for free.

If you could let us know where in the world you are (+/- a hundred miles), more information about the make and model of your receiver, your data collector and software, and your office software we could probably offer more specific advise.

OPUS and AUSPOS work worldwide. Given a long enough occupation. You can make your own control point with a long static file.

thanks you for your message,
Mark Mayer : we want to start a new mining projet in africa (DRC). what i want is to establish 4 control points for the aerial survey.
Mark Silver : can you please shown me how to make the control point with a long static? Im using trimble equipment (R6)

Collect static data. 1 or 5-Second interval (or 15 or 30) will be fine. Carefully measure the height to the bottom of the antenna.

With the static file in hand, visit:

AusPos: http://www.ga.gov.au/bin/gps.pl
OPUS: https://www.ngs.noaa.gov/OPUS/

More suggestions: http://gpsworld.com/7-free-alternatives-opus-post-processing-in-government-shutdown/

M

thanks mark silver, if Im stuck i will comeback

Mark Silver, post: 422279, member: 1087 wrote: More suggestions: http://gpsworld.com/7-free-alternatives-opus-post-processing-in-government-shutdown/

Unfortunately some of the links in that story are dead.

1. How many units do you have?

2. There must be some form of local control to start from.

3. Do you care how close to true you are?

Hi spledeus,
i have got one base and two receivers, the local control point is far from the site ( 120km)

Howdy,

To supplement the other postings, I provide the following verified links and some additional detail.

It is possible to determine a position anywhere in the world using the free automated GPS processing services if you log static data at a point. I would log at least three 24-hour sessions (using a 30-second epoch interval) to achieve the best results but I am conservative on these matters.

Automated processing sites

http://apps.gdgps.net . - NASA precise point positioning

https://webapp.geod.nrcan.gc.ca/geod/tools-outils/ppp.php - Natural Resources Canada precise point positioning

http://www.ga.gov.au/scientific-topics/positioning-navigation/geodesy/auspos -
Australian positioning service

http://sopac.ucsd.edu/scout.shtml - University of California - San Diego GPS positioning service

https://geodesy.noaa.gov/OPUS/ - US National Geodetic Survey GPS positioning services (both Static and Rapid Static)

In 2012 (a long time ago), I assigned a lab designed to explore the differences between the solutions of the services listed above. I included some US-specific comparisons of the computed positions to data published for the site; this is irrelevant to you. See: http://geodesyattamucc.pbworks.com/w/file/fetch/53012749/lab9_2012_summarySolutions.pdf?force_download=1

Hope that link works.

To use these tools go to the link and review the specifics of how they work. In some cases, your data must be converted to RINEX. The option to export your stored GNSS data to RINEX format should be available in your software. Otherwise, I recommend using the TEQC tool. See: https://www.unavco.org/software/data-processing/teqc/teqc.html

Hope this helps.

DMM

120km is not far at all in the GNSS world.

Do not consider what you have as a base and 2 receivers. Establish your control by considering you have 3 receivers, setting three intervisible points that you can do a tight traverse between. You can do that on any project with good precision, then pick one point as a base and use the 2 receivers to complete your project.

Paul in PA

When doing what I suggest above, after your 3 point traverse, you may use one point as fixed and the others as checks or pick a best fit of all three coordinates. I usually do the former, because no matter how good things are one point always seems better. If I have some idea of which point that is, I set up there first and breakdown there last, so it has the most data and a better chance at being the best observation.

For the sake of having three long observations I may set a traverse point that I never need to use for my project.

Paul in PA

Paul in PA, post: 422481, member: 236 wrote: ... after your 3 point traverse ....

I did not gather that Philos has anything to traverse with. Just 3 GPS receivers.

Philos, Few questions. Everyone commenting is assuming that you have a solid grounding in the fundamentals of surveying, but you stated that you are new to land surveying
.
1. What is your level of experience, in conventional surveying, static GPS surveying and RTK GPS surveying? Cadastral surveying? Construction?
2. What is the purpose of this control network, how is it intended to be used in the future and by whom?
3. Do you have any experience and what software are you using for post processing of the GPS data that you intend to collect?
4. Have you identified what mapping projection the finished product will be in?
5. Have you selected appropriate locations for these control points that will have stability, relative ease of access and minimal obstructions of the sky.

The more planning that goes into these, the better the end results. Using 3 receivers I think you will be able to accomplish a great deal. I would suggest starting off by establishing a network using (simultaneous) static measurements, including a tie to the station 120 km. distant. Once you have that firmly established, in the proper projection and adjusted, you can then add density to the network using RTK with your base located on one of the primary control points established via static observations.

I think the more information you provide here, the better people here will be able to point you in the right direction.

Good luck!

philos, post: 422278, member: 12630 wrote: thanks you for your message,
Mark Mayer : we want to start a new mining projet in africa (DRC). what i want is to establish 4 control points for the aerial survey.
Mark Silver : can you please shown me how to make the control point with a long static? Im using trimble equipment (R6)

Looking at his message of Thursday @2132, it appears the control points he seeks to establish are for photo control. He should be able to use the automated tools. As Williwaw points out, we need more details from the person seeking advice.

Perhaps the requirements could be met by ellipsoidal coordinates. He needs to determine both the datum and accuracy standards applicable to this work.

Establishing a control network does not seem to be his goal. If it were there are many other issues involved including monumentation, whether the network is to also support optical observations, whether heights are required. If heights are required, what vertical datum and height type?

Hope this helps,

DMM