State Plane practices

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.

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

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.

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.

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.

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 ....

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.

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.

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.

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.

I shouldn't have mentioned LDP. my bad.

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

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.