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Control Points Using GPS and Total Station
MightyMoe replied 3 years, 1 month ago 18 Members · 32 Replies
We can all learn something from everyone here.
When you’re with professional people, if you’re not being encouraged to ask questions about and for your work, you should find better people to surround yourself with IMHO.
Learning never stops.
When it does, the following stagnation is sometimes disastrous.
I don’t know how that software is set up. Just don’t mix grid and ground measurements. Verify through your misclosure between RTK points and traverse points that you don’t have any significant blunders. The software should apply the SF automatically to the TS measurements. Verify by testing what you’re getting, don’t assume the black box knows all. Test distances measured by TS between RTK points by dividing the RTK measured distance by the TS distance and see if the ratio approximates the SF for that project area. If so you’re likely getting ground and grid measurements mixed. You’re looking for consistency and repeatability.
When in doubt, test it out.
Willy- Posted by: @field-dog
new job in MAGNET Field, a SF other than 1 was already set
Since starting with GNSS is your approach, I assume you want to work on Grid datum.
The combined scale factor not already “set” in Magnet. It is computed by the Magnet field software. The combined scale factor changes for every position on the face of the earth based on the distance from the central meridian and the elevation. Since Florida is very flat, this computed CSF will work just fine. No need for you to compute or create your scale factor. The software will properly apply the CSF to each EDM distance. No further thought needed. One thing to remember, only apply the CSF to distances. Never apply CSF to coordinates.
Some interesting findings on integrating observations, including post-processed RTN vectors, into control networks. Just came out last week.
https://www.oregon.gov/odot/Programs/ResearchDocuments/SPR304-821_UpdatedSurveyStds.pdf
- My additions in BOLDPosted by: @field-dog
This is a rehash of https://surveyorconnect.com/community/surveying-geomatics/gps-and-total-station-used-together/paged/1/ (March 25, 2011 4:47 pm) by yyamahayzf. My procedure using RTK for a boundary survey would be:
- SET DATUM. Calculate scale factor. RECORD METADATA: Date-Who-etc!!!
- Set 2 points at each end of the traverse
- Observe each point twice for 3 minutes (BREAK FIX BETWEEN EACH OBSERVATION), a minimum of 4 hours apart
- Traverse using doubled angles, scale factor (SF) = 1 in data collector
- traverse through closing two points.
- Adjust traverse
- Hold two single farthest points on each end,
- one as basis of position, the other end will allow you to calculate the basis of bearing
- and rotate
- Apply scale factor.
- Decision: Scale traverse to RTK observations or scale RTK to Traverse?
- For me, this would depend on a few factors. Most likely, I would scale the whole thing to state plane and hold the RTK observations.
- Compare distance close and close to two additional points.
- Hold two single farthest points on each end,
- Compute SF
- Enter SF in data collector
- Begin collecting data
-All thoughts my own, except my typos and when I am wrong. Thanks for the link! Going to dive into this one tonight.
I’ve been mixing RTN/RTK vectors with static, conventional and level observations for years. It will be nice to have a recently published paper validating the workflow and exploring the pros and cons…
“…people will come to love their oppression, to adore the technologies that undo their capacities to think.” -Neil Postman- Posted by: @lukenz
Any chance of a summary for us here?
Sorry for the formatting, I pulled this directly from the text:
Abstract: Two control survey networks, observed via a traditional survey campaign and NRTK surveying campaign, were established at two independent study areas. To assess the performance of different surveying scenarios, a least squares adjustment was applied to all available traditional survey and NRTK data to create a reference dataset for each project site. Key findings: 1) When four 5-minute independent NRTK observations are made per point and the resulting baselines are adjusted using the Hybrid Network Methodology, a network accuracy of 1.8 cm in the vertical and 1.0 cm in the horizontal at a 95% confidence level is achievable. 2) Two hours between repeat observations is recommended to achieve fully independent solutions. 3) Total station (TS) observations improve overall horizontal accuracy of the network. 4) If vertical accuracies less than 1.8 cm at a 95% confidence level are required, then differential leveling should be performed. 5) When TS and differential leveling survey is required, not all stations need to be occupied with NRTK. 6) When NRTK observations are suitable for a project, static GNSS may not be required. 7) It is not recommended to hold the RTN published coordinates as a constraint in the adjustment. 8) It is recommended that RTN network managers ensure the published coordinates for the RTN base stations align with the NSRS. 9) Observing control stations with NRTK removes the requirement of having a minimum of 2 GNSS receivers observing points simultaneously.
“…people will come to love their oppression, to adore the technologies that undo their capacities to think.” -Neil Postman It is a pretty comprehensive research project and report commissioned by Oregon DOT with Oregon State University. ODOT wanted to see if they could improve efficiencies, without losing accuracy, for setting project control in comparison to their previous standards/procedures. One of the drivers was to see if they could use their robust RTN for control, in lieu of longer static sessions.
Ditto.
- Posted by: @mark-mayer
Presuming that you are using NAD83(2011) then Geoid18 is the datum to use. Of course, if elevations are not required the geoid question is moot.
That should read: Presuming that you are using NAD83(2011) then Geoid18 is the model to use.
State plane was developed to make a standard projection to allow surveyors to simulate surveying on a plane over semi-large areas.
To do this it was necessary to lay out a “plane” through a sphere. This means for most projections they lay under the sphere at the central meridian (Transverse Mercator like FEZ) and exit the sphere east and west of the center, this is rotated for a Lambert Zone. For Transverse Mercator projections that means that east and west of the central meridian the plane intersects the sphere and therefore the grid scale factor will be 1 along those lines. Along the central meridian the grid scale factor will be less than one. The Florida East zone set a scale factor along the central meridian of .9999411765. It is possible to develop a tangent plane that is 1 along the central meridian but US State Plane Zones don’t do it that way.
A eyeball calculation would show a 10,000 foot surface distance along the central meridian (W81d00’00”) at 0 ellipsoid height would reduce to a state plane grid distance of 9999.41.
So there is a scale factor already set when you load up your state plane projection. This doesn’t include the height scale factor. However in Florida it should be a minor consideration.
The radius of the earth is roughly 20,906,000 feet so each 20 feet of elevation change is 1ppm because the height scale is a divided ratio. So at 20 feet in height the a surface measurement of 10,000′ will reduce to 9999.40 along the central meridian. I suspect a height of 200′ would be unusual there but even that would only cause an additional reduction of .10′.
From the central meridian of W81d00’00” moving east and west the grid scale factor will shift closer to 1. Because Florida chose a scale factor so close to 1, I’m thinking the grid scale of 1 and greater may be in play along the coasts. This would mean the plane intersected the sphere and could lie above the survey. Then the grid distance would be longer than the ground distance.
Wanting a scale factor of 1 may not be something to even think about in that environment.
The important thing is to learn just what your “error” budget is for distances, what your actual scale reductions are at your project site and then respond accordingly.
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