We are considering setting up a control network around our city to use as main control to bring in control to jobs throughout the city in the future as new projects arise. Our initial thought is to create a "box" around the city with static points that are easy to access with a few scattered throughout the interior of the city.
We have done something similar to the above in the past for route surveys that stretched a few miles but that has been close to a decade now, so we are attempting to relearn as much as we can so that way we get started on the right foot and most importantly not wish we would've done things differently in years to come, since we hope to be using these control points until we have one foot in the grave.
Thanks in advance.
Can you just use existing CORS?
I have no idea of where you are or how crowded your city is but some fundamentals are the same no matter where you are. :gammon:
Follow the basics of surveying. Always Always work from the whole to parts, often see people get lazy and run loops of loops of loops and do not make use of their primary networks to begin with.
I would ensure the primaries stations are well established and tied in properly on the outskirts of city, After that is done run ties in the city connecting various parts of primary controls together.
Once you run through all your controls, remember to use least squares for your adjustments since you are going to have plenty of redundancies. Again, not sure how big your city is or do you use scale factors for them? (had a job railway, the surveyor used scale factors to adjust which one plan closed really well but on the ground the track layers had an excess 200mm track)
There are lots of ways to tie it together. Have plenty of redundancy in measerements so the least squares has enough to chew on.
But down the road you will lose some of the points to new development, road or utility work, or landscaping changes. Make stability and survivability high priorities in choosing.
In many areas the 82 year old C&GS bench marks have a 1/10 or 1/4 survival rate, and most of the destruction has occurred in the later decades. If you are planning to use your network for a decade or two expect significant attrition.
You may also want to ponder the effect that the 2022 datum change will have on the usefulness of your data.
sirveyr, post: 450580, member: 6680 wrote: Can you just use existing CORS?
Not sure what that would intel honestly. I stepped away from surveying for a few years and i prior to that I worked for a company that was behind the times on technology and very new to gps. So somedays I spend more time learning what I didn't know or shouldn't have forgotten.
Can you tell us a little more about the size of your town and just what you envision this control network doing for you? Would you expect all local projects to be tied in to this network for example?
One thing you could do is set up a permanently operating RTK base station. With a 35 watt radio broadcasting anybody could use it within a 10 mile (or more) radius. Would that cover your town? Then everybody would be on the same system.
Mark Mayer, post: 451578, member: 424 wrote: Can you tell us a little more about the size of your town and just what you envision this control network doing for you? Would you expect all local projects to be tied in to this network for example?
One thing you could do is set up a permanently operating RTK base station. With a 35 watt radio broadcasting anybody could use it within a 10 mile (or more) radius. Would that cover your town? Then everybody would be on the same system.
I would want all jobs inside the "box" on the network. We cover several counties becuse we are so new but for this network I believe a 10 mile radius around our hometown would work fine.
Forgive me if I'm speaking stupid here but our rtk base units run off a 35watt radio (TDL450H) I believe. We are lucky to get 2 miles with the base in a prime spot with a 12' radio antenna. How is your suggestion different? Not arguing just trying to learn
2 miles?! There is an issue with your equipment, or someone is crushing your signal. If we're running 35w, we go up toward 8 miles through forest.
We could get 12-13 miles in west Texas with the TDL450H. But that was a 25' antenna at the base and rover.
Going back to the original question, do you know if CORS exists in your area?
Raybies, post: 451586, member: 9029 wrote: But that was a 25' antenna at the base and rover.
I don't think I'd want to haul a 25' antenna around with my rover. I'd go to a repeater (or better yet: cell service, if available) first.
Hixon (Fort Collins Co) makes a fine 25' prism pole. I have one. I also have a 20' one. Good mast!
N
TXSurveyor, post: 451583, member: 6719 wrote: Forgive me if I'm speaking stupid here but our rtk base units run off a 35watt radio (TDL450H) I believe. We are lucky to get 2 miles with the base in a prime spot with a 12' radio antenna. How is your suggestion different? Not arguing just trying to learn
You may have your 35 watt capable radio on one of its lower power settings.
Mark Mayer, post: 451595, member: 424 wrote: You may have your 35 watt capable radio on one of its lower power settings.
It's set as high as it will go
Just to clarify. When i say prime location, i mean prime location for the piney woods of east Texas. Which isn't too prime. I've honestly never heard of anyone getting more than 2.5 miles of radio reception in my area
TXSurveyor, post: 451597, member: 6719 wrote: It's set as high as it will go
Then you have a hardware problem.
Here are some helpful links. The first, is a link to RTKNet. It is a Trimble VRS pay-for service.
http://wds-us.com/coverage-map/
Anywhere within the green polygons, with cellular service, you should expect excellent RTK GPS results. I miss having a good VRS around, let me tell ya. We used to establish control points with two 3-minute observations in opposite directions (ie facing north and facing south) via RTKNet. That was 5 years ago, so you could probably get away with two 1-minute these days!
The next one is straight from NGS.
https://www.ngs.noaa.gov/CORS_Map/
Judging by the second map, there are a few areas in East Texas that have 60km+ baselines to CORS, so you're looking at a longer session for static occupations.
So, yes, you can make your control network. How you observe it depends on how many GPS units and how many control points. If only two receivers, I would run them 2 hrs at a time, leap frogging sessions. A and B, A and C, C and D, D and B, etc. Then I'd post-process them in your suite of software. IF that is beyond your comfort level, you could also submit them to OPUS. But, you'd lose that baseline between receivers in doing so.
I hope that helps,
~Raybies
My needs of a network is for land surveying and maintaining bearings that related to sun shots and compass based directions.
I've been building my own personal WGS84 static wagon wheel shaped networks with legs of 3mi to 5mi across NE Texas and some of them have been connected together with great success and many are still independent.
TxDot values are my control.
I can't see doing a large scale project without it in some form or another and be competitive and maintaining being competent and assured of the results.
TXSurveyor, post: 451598, member: 6719 wrote: Just to clarify. When i say prime location, i mean prime location for the piney woods of east Texas. Which isn't too prime. I've honestly never heard of anyone getting more than 2.5 miles of radio reception in my area
You might want to double check those settings. I can get over a mile with just my internal 1 watt radios and without a raised external antenna. I don't know much about your location, but I am in the land of the long leaf pine - and very little topography. If I need more distance I raise the antenna to 15-feet.
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