State Plane practices

[Norm]

Your basic understanding is correct. I suppose you are going to get all kinds of advise that could seem overwhelming. Doing what you are asking about is fairly simple. Take your total station measurements applying a combined scale factor for the area of the traverse thereby establishing state plane grid coordinates on your traverse stations as you go. This CSF is most easily determined using https://www.ngs.noaa.gov/NCAT/. Using Lat Long and orthometric height from google earth or some other source on a central point of your traverse will be sufficient on relatively small traverses. The new state plane coordinate systems coming soon to a traverse near you will allow you to measure with a factor of 1 unless you are in the mountains. This advise is based on the realization no measurements are without error and the errors introduced by using this advise is absorbed to an acceptable level for the scope of most aerial survey requirements.

• This reply was modified 2 months, 1 week ago by  Norm.
• This reply was modified 2 months, 1 week ago by  Norm.

ngs.noaa.gov

NGS Coordinate Conversion and Transformation Tool (NCAT)

NGS Coordinate Conversion and Transformation Tool (NCAT)

[Caleb]

What about if grid to ground is calculated in your data collector?

[Norm]

If the settings in the DC control the TS don’t mess with the TS. And it never hurts to remove the DC from the picture to compare results so that you know the DC is set correctly. We saw this misunderstood and misapplied up so may times we designed LDP to overcome it. LDP for all intents and purposes is a Cartesian system with a scale of 1 for total station work.

[Caleb]

So locating monuments miles apart with the DC set at grid to ground should use LDP to reduce error? Honestly just trying to wrap my head around this. I don’t typically don’t survey parcels with lines longer than 3000 feet long, so I want to make sure my data is precise as can be.

[timd1971]

https://youtu.be/GIylUUmz0sk?si=LlM1uQpduqgjLoaB

[Norm]

LDP vs state plane for long traverses is not the issue. LDP is no better than state plane for precision or accurate survey grid results . Its understanding how to use the system. In the day in which we live TS traversing between GNSS surveyed geodetic monuments miles apart seems like a waste of resources to me. We never had to traverse more than half a mile with a total station to reach a GNSS control mark in the past 20 years. Of course we were intentional about establishing a good GNSS control network so we didn’t have to.

One basic reason for LDP:

To use a scale of 1 for for grid and ground. One set of coordinates per point.

• This reply was modified 2 months, 1 week ago by  Norm.
• This reply was modified 2 months, 1 week ago by  Norm.

[thebionicman]

Doing proper geodetic calculations puts SPC and LDP on nominally equal foiting. Running SPC and using a blanket combined factor may or may not be as good as developing an LDP. It depends on where you are in the projection and how your terrain relates to the projection.

I have developed countless projections that use terrain to offset distortion and vice versa. It doesn’t sound like that’s what you need. Set the local site with an average 1/csf and scale point and get to work. If you aren’t changing elevation or traversing miles you should be fine.

As an aside.. If the panel point is unsuitable for GNSS I question the value of the point as aerial control ….

[Norman_Oklahoma]

Dittos on what Norm has said. Said another way – If you set your data collector to the appropriate state plane system, and load state plane control coordinates into it, the gun/dc system will make measurements at ground and apply the appropriate scale factor to them in computing coordinates.

At this point I wish state, in the interest of clarity, that – to the surveyor – the coordinates are not raw data, coordinates are the product of raw data. This is a common misconception. The engineer or architect you deliver to may consider the coordinates to be ‘raw data’, but not you. Raw data is the measured angles and distances, the measure ups, the point codes, etc.

In practice if you are going to work in a grid system you are going to rely on some software or other to do the calculations. I prefer StarNet but there are lots of other options. Collect your raw data, feed it to the software, get coordinates and other information out.

[Norm]

Right there is what I mean about confusion. Now he’s been told to work with CSF and 1/CSF. The question is regarding using a TS to survey on the state plane grid. In that situation you use the CSF in you ground measurements, not 1/CSF. The CSF reduces your ground TS measurements down to the grid in most cases and keeps the point coordinates grid. 1/CSF is for raising and modifying state plane grid coordinates to the ground. It is used for GNSS observations, not TS and the result is not state plane coordinates. I knew this topic could go sideways. It always seems to.

• This reply was modified 2 months, 1 week ago by  Norm.

[Norman_Oklahoma]

I’m entirely in favor of LDPs and use one in my daily work. But a fellow who is asking about the basic mechanics of working in a grid system is going to be completely overwhelmed by an LDP if one is not already preloaded in his dc and other software.

[john-putnam]

Happy fourth form Denmark.

First, an LDP (low distortion project) and SPC are mathematically identical. An LDP normally covers a targeted area and utilizes the projection’s scale factor to account for terrain and the seal-level correction factor. The confusing point is how LDP is sometime used to refer to ‘local datum plane’ which is coordinate system where the true grid points are manipulated by the combined scale factor (grid scale x sea level correction) that best represents the project. (Side note, hopefully the resulting coordinates have been truncated so as not to be confused with true grid coordinates. Remember, friends don’t let friends scale without truncating.) Local datum planes generally work only in small areas. A good reference is the Oregon Dept. of Transportations ‘OCRS Handbook and Users Guide’ at ‘www.oregon.gov/odot/ETA/Pages/OCRS.aspx’

Going out on a limb here, but if the GNSS derived photo control is to be delivered in SPC then the TS derived coordinates need to as well. All of this talk of LDP vs SPC in confusing the matter. I’m old enough to have had to calculate SPC coordinates from raw TS measurements by hand. In theory it is very simple, it just some complicated/repetitive math if you have to do it from tables. An individual combined scale factor is calculated for every shot as follows. Every measurement is reduced to a vector from the instrument to the point of interest. Grid scale and sea-level corrections are computed and multiplied to establish the combined scale factor at the each end (okay, I now it is not the true grid scale at the point of interest but it is close enough). (Pro tip, don’t use google earth or a quad map to come up with the elevation, use the mean of the vector. If you are shooting across a canyon or from mountain top to mountain top then you don’t care about the ground elevation at the mid point) Then you mean the CF at both ends of the vector to establish the CF for it. Next divide the raw vector by the CF holding the instrument point and Bob’s your uncle. Simple, just time consuming. Better to just let the DC do the work for you. I can not think of a modern instrument or DC that will not handle this. Just set up the project in the appropriate coordinate system and make sure it is set up to utilize the combined factor. With a little investigation, you may find that for shorter shots the CF may be so small that it is lost in the noise.

Whatever you do, do not come up with a project CF and apply it only to the TS shots.

oregon.gov

Oregon Department of Transportation : Oregon Coordinate Reference System : Engineering Automation : State of Oregon

The Oregon Coordinate Reference System is based on a group of low distortion map projection coordinate systems. Low distortion projections are based on conformal map projections designed to cover significant portions of urban and rural areas of Oregon.

[Norm]

I shouldn’t have mentioned LDP. my bad.

[Caleb]

Glad you did. I appreciate your help Norm, thank you.

[MightyMoe]

If you’re working in state plane there should be nothing you need to do about TS shots except to make sure that all your Data Collector programs are properly set-up to accommodate the projection.

I’m the last guy to review all the various instruments and programs. I’ve only used Wild, HP, Topcon, Trimble, I can’t really speak to any others.

But, since the mid 1980’s this has been SOP, the DC takes the vectors and calculates the coordinates how it’s told to do. The proper way to do this is to take the terrestrial measurements and then calculate the resulting Latitude, longitude coordinate of the forward point, from there the SPC coordinate is derived from the formulas for that projection using the LL coordinate. No matter what the height/elevation of the LL pair it will have only one SPC coordinate since it’s a projected value where the LL coordinate intercepts the surface of the plane projection.

In the hand calculating days that was a painful process and everyone cut corners usually using a project derived scale factor for the distance reduction, sin, cos applied to the bearings and multiplied to the plane calculated HD then a simple add or subtract to the instrument easting-northing for the forward coordinate. For large traverses each distance needed to be reduced to SP.

About 1980-1981 at least one vendor created a program for the old HP calculators to calculate the forward L,L coordinate (you needed elevations for that, usually trig-leveled) which used the actual measured surface distance irrespective of the plane distance, then a second program to calculate the SPC coordinate using the LL. Thus, eliminating any need to ever reduce a distance to State Plane. Again, a bit of a pain to run data through two programs, but a huge jump from the days of doing it on paper.

Today, that’s all been organized, if your programs aren’t doing it, you need different equipment.

I always caution everyone to test your equipment against real world data, don’t simply read the manual and punch buttons. Go to the field, set up the instrument take measurements, make sure it’s all working how it should. If you have a SPC job but small scale factors and short distances it may not be apparent. Then I would suggest a test using a different SPC zone than where you are surveying, then you will get the scale factors large and test numbers should jump out.

If your DC is not properly reducing the surface distance, something is very wrong. Trying to reduce the surface distance by changing the TS settings each job is a bad idea and it may be working against you, basically reducing it twice.

[Native1]

Thanks for the replies.
I’m still reading, still learning – same as any other day.

I had thought I’d be able to set the data collector up in a mapping plane, proper zone, datum, geoid, etc and run GNSS points on the targets, AND THEN use the total station for the targets that I can’t get proper satellite views on – all with the mapping projection. So basically using the total station in “grid” and keeping everything relative.

I tried this on another job recently and the data collector would not let me take a backsight. Wouldn’t do it. My chief had done a site calibration prior (which i highly disagreed with at the time) and the data collector “protected” the control points, and no amount of manipulation was allowed to any of the data afterwards. I couldn’t undo it per se. Couldn’t make typical elevation, rotation, translation adjustments. And no backsights, etc etc. But I think the solution is to not calibrate this time, which I wouldn’t anyway at all. That has its place and I have no idea why that was chosen.

But this time my plan was to collect the points GNSS, then use the TS in that same mapping plane to transfer SPC to the “tough” targets, so to speak, and handle it myself.

For reference and any haters, this is mountains, canyons, 45 acre site. ONe target is a mile hike on top of the only flat spot on the east side, and it’s opposing target location is on a road in a canyon. 600-700′ elevation difference between them. So it’s been a challenging job to plan up and try to execute. We have to get creative on every target with the budget.

[timd1971]

Curious. What equipment or more particularly which DC software are you using?

For those that use DC software that can utilize switching between BOTH GNSS and Total Station prisms on the fly, I would assume all of this is handled automatically? Do you have to enter the combined scale factor at the start of the project for the region (or custom scale factor) or does it know automatically depending on your State Plane CS chosen?

[MightyMoe]

An LDP for that type of site would be simple to construct in Trimble, if that’s what you’re using.

Put the surface at the elevation mean of the site, put the central meridian near the east-west center and then you never need to think about the Total station again, at those elevations you might be looking at 20ppm at most or .02’/1000′.

I don’t understand what locking away the control points would mean, but I suspect you could enter another point on top of each control point and use those.

[Native1]

We’re using a Trimble S6 instrument, and the SurveyPro software on a Ranger 3 collector.

On the office side, there’s zero support. They use Autocad and civil3d only.

As for “locking” the controls points..When my chief did a calibration on another job with the Trimble R10, it pairs a ground point with a GNSS control point and “protects” them afterward from any sort of manipulation. I can’t rotate or transform anything in the collector afterwards. Can’t set up and backsight on them with the total station, etc etc.
Even after I try to move on and do something else job-related. It’s like a permanent fixture at that point.

So I pulled the coordinates I needed, put them in a new job, and went on topo’ing to get the job done.

This time around my goal was to start it off right, know the processes beforehand, etc etc. Have an actual plan.
I’m taking the reigns because I just was not happy with the workflow and the results last time.
I’m also studying/reading every day to answer question

[Caleb]

If the points they are locking are in civil3d you can unlock them, if you wish. I saw on another post you go to UMaine. I have a MS in Data Science from there are you in Maine or out of state studying online?

[Native1]

oh ok, I didn’t know that about civil3d.

MS in Data Science- impressive. I just started at UMaine online going for the Surveying/Engineering Technology bachelor’s degree – I live and work in California for the time being. I brought in a an associates and have about halfway to go yet.

I am slated to take the Carlson/civil3d course this fall, so I am hoping to learn more about field to office processes.

• This reply was modified 2 months, 1 week ago by  Native1.