@mathteacher Except MightyMoe's example above shows with different combined factors you end up with the same plane coordinate but different ground coordinates. If the software acted as you suggest, then both sets of ground coordinates should be the same and the plane coordinates would differ.
Enter this one in the plain old Google search window: can i enter 1 as a combined factor in a trimble total station?
But look carefully. In the second example, the one with CSF = 1, his entered coordinates were the GRID coordinates from the first example.
The CSF = 1 preserved the value given to it.
Yes, I definitely agree a CSF=1 will preserve the value given to it, but the value given to it is the plane coordinate.
Do your google search and look at the second result, Trimble field systems help portal, To set up a ground coordinate system and item 5.
To use ground coordinates with the selected coordinate system, from the Coordinates field, do one of the following:
-
To key in a scale factor, select Ground (Keyed in scale factor). Enter a value in the Ground scale factor field.
The number entered should be the inverse of the combined scale factor for the location of the job.
The reason you need to enter the inverse of the CSF is because the operation is being performed on the plane coordinates not the ground coordinates.
If this discussion doesn't scare you enough to use SPCS2022 as ground it should. We saw the scale settings mishandled by the users and the software enough to create 14 zones to cover our state a dozen years ago and called it good. I realize some of you don't have the luxury we do in terrain that lends itself to large LDP areas but geez louise, many of us still are determined to screw this up no matter what it takes.
Yes, Trimble collects ground and modifies it according to what's set up. Note, though, that 1 would tell Trimble that the collected ground coordinates are the same as the grid coordinates that you want to use, hence no adjustment is needed.
I think that Trimble is well aware of this ambiguity and usually glosses over it in presentations. If you watch the video that I linked to, at some point somewhere between 27 and 33 minutes, the guy says, "...if you haven't entered 1 in your total station." There's another reference a few minutes later.
The real empirical test is to use Access to collect a couple of points with state plane specified and CSF = 1, then collect the same points in a different job with state plane specified and no CSF entered.
If i'm right, the coordinates will differ by the state plane combined factor at that location.
Indeed! So, what's your opinion of the results from the 1? It seems that there's no wrong answer.
Yes, and that's the way a lot of people interpret it, But I think that Trimble always measures (or calculates from GPS) ground distances and then applies a projection if one is specified to get grid coordinates. Now, there's confusion here between "local grid" and "grid." Trimble seems to define "local grid" to be its ground coordinates and then applies combined factor to get its "grid" coordinates.
But the scale factor set to 1 overrides that calculation. The software interprets the 1 to mean that grid coordinates, which it wants to calculate, are the same as local grid coordinates, which it knows.
Don't LandButcher and OleManRiver think that 1 means ground?
If I called Trimble, I would be labelled spam, but a Trimble licensee could call the guy Mark something in Georgia who did the video I linked to somewhere above and settle the question once and for all.
It would be great to have Trimble verify one or the other.
I don’t think 1 means ground or grid. It means 1 to whatever you are in when using Trimble. But you don’t key in the c/f in Trimble. You key in a ground calculated factor at some point of origin if you want grid to be ground. When choosing the coordinate system in Trimble access or TBC you simply choose the datum and coordinate system Va state plane south zone. So NAD83(2011) VA south zone. Then a geoid model is optional but geoid18 . I then simply survey. No keying in anything except an ellipsoid height in the field data collector which is a rough ellipsoid height for that project. I am in state plane grid the whole time no matter what the tool is I use gps RTK or total station. In the office I will scale to the surface I can see in TBC for every point a scale factor an elevation factor and a combined factor. That is just like NCAT. Now when I scale to ground I can choose a point for the origin horizontal and a totally different point or type in the elevation or the ellipsoid height. It then computes the reciprocal of that. Cf basically and projects everything up to the surface or down. Now in Trimble access which in my other post I alluded to. There is a setting to reduce t sea level or ellipsoid. So total station work when on grid settings is reducing the the distance after all other things are done first tempature pressure difference in height curvature and refraction so corrected zenith angle is correct then it creates the horizontal distance at the mean between the two points reduces that to the ellipsoid then it is projected up or down to grid. If you did not have an ellipsoid defined it will use it’s version of the wgs84 ellipsoid. All GNSS all robot total station is done on the ellipsoid or reduced to it before it re projects. When you choose a datum and coordinate system. Now there is a use for a coordinate system that has no projection scale only and by default it is set to 1. Now it is 1 to ground whatever your total station is on. No gps is done in this system. Believe me I have had many phone calls from crews back years ago and recently where hey I can’t see any northings and eastings. I say you are working with gps right now yes sir. I say go to review job an tell me what is said for your coordinate system. Scale 1.00000000. I say change that to what it’s supposed to be. Oh you mean like NAD83 Va south zone yes. Ok I am good now. lol. 1 x’s anything except 0 is the same it was before. So 1.00000 entered as a factor doesn’t change anything. The one thing to watch is when you do want to convert grid to ground is especially in a few places here is to make sure it does not = 1.00000. Or no coordinate will change. And you are correct it is mathematically possible for a scale factor x an ellipsoid factor that could produce a cf to be 1.00000000000. Usually I don’t put myself in that situation because before I scale to ground I always see what the error well distortion is for my project. I see no reason to scale if it’s in the weeds of me not impacting anything I do. I will simply stay in grid. We only have about .10 ft per 1000 anyway here and at the parallel it’s even smaller in some of the counties i work in. For example I had 50 acre boundary that was not going to matter if I was in grid or ground it was so minute and in the weeds . Go to a different location I scaled to ground because it could make a difference between grid and ground.
@norm lol you are so correct. I have seen just about everything. Here is one for the Trimble folks. A guy had some grid coordinates the office assigned a 0 elevation to once. Because cad for ever said 0 or that -9999999 thing. Well guess what happened when his collector was set to state plane and he took his BS yeppers a big fat distance error. His true elevation was around 350 ft. He set up on some better control that had the correct elevation. It checked he shot the other two points. And said well we must have some bad foot ages. Nope. You just had a computed distance at 0 elevation on a projected system and you said it was elevation 0. Now I always strip the 0 bogus elevation off. That’s what the average project height is for. If no elevation is needed no number is placed. I leave it blank. Undefined. Works great.
"I don’t think 1 means ground or grid. It means 1 to whatever you are in when using Trimble."
More precisely, it's applied to whatever state the coordinates happen to be in.
Trimble collects a point.
It looks to see what projection to adjust that point to.
If there's no combined factor. it computes the combined factor based on the projection it has and applies it.
If there's a combined factor not equal to 1, it applies that combined factor.
If there's a combined factor equal to 1, it assumes that what you collected is what you want. Since it collects ground, ground is what it saves. Now some literature says that Trimble assumes that the collected point is already in the chosen coordinate system. When state plane is the chosen system, that leads users to believe that they've saved a state plane coordinate when they really saved a ground coordinate.
It has to be a throwback to a earlier time that needed to be preserved for some reason, or 1 as a CSF has to go one way or the other (you wouldn't want the system to halt and catch fire if it encountered a 1), so Trimble chose to preserve what was collected.
@mathteacher My opinion is that for 99% of surveying purposes any distortion less than 20 ppm between grid and ground is not worth discussing other than for amusement.
@mathteacher in reports in Trimble if you are straight up state plane it will show 1.000000. If you scale to ground in state plane it will show the origin so lat long and the ellipsoid height used and the ground calculated scale factor. Which is the combined factors reciprocal in theory. Again scaling from a single point is not the most mathematical correct but it works on most sites. Now you can see all the cf. for every point with an elevation or ellipsoid height. In TA. It uses both points and computes the mean of the line from both CT’s at each end to stay on grid. I think you are getting it. But you do not enter a cf ever in Trimble access. It has everything it needs. So in a lambert the scale factors are at the latitude. That’s the only place they change. The elevation factor or truthfully ellipsoid factor for NAD83 2011. It can now compute all it needs it also should be chosen the geoid model etc. so it can go from a total station distance at ground reduced to ellipsoid then projected. To grid. I think that’s what had me spinning my wheels is someone entering a cf in Trimble access to convert ground distance to grid. It’s not part of the process. The exception to all of this is if you don’t key in a rod height so no elevation at the rod so it now reverts to the project height you set and the one at the robot or if it’s not a elevation or height it uses the scale factor and that project height to compute a cf in the back ground to get total station data to grid. I too can’t wait for the new datum. I despise all the scaling stuff. Here when people scale they leave it looking just like state plane. So no meta data so you are reverse engineering a project half the time to try and figure out if they scaled or not. I do my part and always give the LS all the meta data Some use it some do not. Once those points go into cad they are just points to the drafter and they lose there meaning along the way unfortunately.
the reason most leave them looking like state plane is so engineers can see them on the geolocation imagery. Which I believe I could lol of a false northing and easting and give them the parameters and I would assume they can key that info into cad and it would still work for the geolocation stuff. But I am not a cad personal I have no idea how that works in Carlson cad or civil 3d which are the big two I see being used. So I bite my tongue scale and leave them looking like state plane until I am in charge lol.
If this discussion doesn't scare you enough to use SPCS2022 as ground it should. We saw the scale settings mishandled by the users and the software enough to create 14 zones to cover our state a dozen years ago and called it good. I realize some of you don't have the luxury we do in terrain that lends itself to large LDP areas but geez louise, many of us still are determined to screw this up no matter what it takes.
From your post above you mentioned 20PPM. I agree completely within 20PPM using a projection what the heck are you doing adjusting any distances. Some get so caught up in the math they forget what the purpose of the job is. .02' in 1000' is plenty accurate for almost every task associated with typical land surveying. With any project you should analyze your error budget, what is acceptable.
The new 2022 western zones are attempting to capture 90-95% of the population within 75ppm or 1:13,000. This is very much pushing the limits, I can't see DOT thinking that's acceptable, but of course it's going to be a case by case basis. The way it's being done is changing the CM GSF (TM projections) to a greater than 1 number. This puts the grid surface well above the ellipsoid so it's closer to an actual ground elevation. I don't really know why that wasn't done originally with NAD27. Having the grid so far underground was never optimal. I do know with chatting with some of the designers of NAD83 they couldn't stand the idea of grid factors in the zones greater than 1. I think that goes back to the days of calculating each distance using interloped grid factors and trying to stop the confusion of the .9999 something number crossing over.
The proper way to calculate a grid coordinate is to grind through the math of the geodetic calculations. If you have one of the old Blue Books you can learn how to calculate forward Lat, Long positions from a terrestrial survey, then the reduction of the Lat, Long to the grid number. That's how it should be done, that's how Trimble does it; at least I've always assumed that's how it's done in Trimble, but I don't have the code. From there it's trivial to calculate a "close to ground" number. The distances in SP never concerned me, it was always the rotation that is the vexing issue. Some zones get up to 4degrees and that's a difficult number to deal with. Cardinal equivalents are an important land surveying issue and SP isn't designed for that.
Last unsolicited post on this matter. Here's what ChatGPT and Google say about each other.
This to ChatGPT:
ChatGPT said:
That Google competitor is technically wrong in practice, and here’s why — though it's an easy mistake to make if you're only reasoning abstractly and not familiar with how Trimble Access is actually implemented.
Let’s break this down clearly:
🚧 THE GOOGLE COMPETITOR'S REASONING
Their logic:
“Access is set to a state plane coordinate system (SPCS), and the CSF = 1, so Access must project the GNSS data to state plane and multiply by 1. Therefore, the coordinates are in state plane.”
This soundscorrect but misseswhat Access actually doeswhen CSF ≠ default.
✅ WHAT TRIMBLE ACCESS ACTUALLY DOES
Access applies the CSF to “flatten” the data to match ground distances.
If you manually enter CSF = 1.0, you are telling Access to suppress the projection scale factor, effectively backing outthe distortion from the SPCS projection.
So what do you get?
-
Coordinates that look like State Plane (since the origin, rotation, and axes are defined by it),
-
But whose distances are ground-like, not grid.
-
These are not true state plane coordinates — because if you measured 1,000 ft on the ground, your coordinates would show 1,000 ft apart, even if the local grid scale factor was 0.99998 (i.e., state plane would show ~999.98 ft).
🧮 THE KEY IS IN HOW ACCESS HANDLES DISTANCE SCALING
Access always:
-
Projects the GNSS position to a 2D coordinate system (like SPC).
-
Applies the combined scale factor (CSF)to adjust the projected coordinate so that:
-
Slope distances ≈ horizontal distances ≈ coordinate deltas.
-
If you set CSF = 1:
-
Access suppresses the projection’s natural distortion.
-
Coordinates preserve ground-level geometry (local surface distances).
-
The resulting numbers look like SPC but aren't SPC.
🧠 WHY THIS MATTERS
Many users misinterpret this behavior.That’s why:
-
Some say “Use CSF = 1 to work in ground.”
-
Others mistakenly believe CSF = 1 means “unchanged SPC.”
But Access is distance-true, not coordinate-true. Its job is to flatten the worldto make your local measurements reflect local geometry.
⚠️ THE PROOF IS IN THE DISTANCES
If you:
-
Set your job to SPC + CSF = 1
-
Collect two GNSS points 1,000 ft apart on the ground
-
View the coordinate difference in Access or TBC
You will see:
-
A delta of 1,000 ft, not 999.95 ftas state plane would give (if GSF = 0.99995)
That tells you unequivocally that the coordinate system is no longer SPC — it's a SPC-based framewith grid distortion removed.
🧭 SUMMARY
| Claim | Verdict | Why |
|---|---|---|
| CSF = 1 + SPC zone = SPC coords | ❌ Incorrect | Coordinates are flattenedto match ground, not preserved as grid |
| Access always projects GNSS to SPC | ✅ True | But what it storesdepends on CSF |
| CSF adjusts projection distortion | ✅ True | That’s its entire purpose |
-
Misunderstanding of Scale Factors:The combined scale factor is not a single, fixed value. It's a product of the grid scale factor and the elevation factor. These factors account for the distortion caused by projecting the Earth's surface onto a flat plane and the effect of elevation.
-
Contextual Confusion:The terms "ground coordinates" and "State Plane coordinates" are often used interchangeably, but in Trimble Access, they have distinct meanings within the software's coordinate system setup. Ground coordinates represent actual distances on the Earth's surface, while State Plane coordinates are the projected, flat-plane representation.
-
Software-Specific Behavior:Trimble Access has specific ways of handling scale factors and coordinate transformations, which can vary from other software or methodologies. ChatGPT might be relying on generalized knowledge instead of understanding the intricacies of the software.
ChatGPT: a cluster tuck
If this discussion doesn't scare you enough to use SPCS2022 as ground it should.
I thought I watched a NGS webinar 6 or 8 months ago where a viewer asked the NGS presenter if they'd still need to scale from the new state plane and the NGS guy said yes. Is that not the case? Or am I misunderstanding what you're saying here.
If this discussion doesn't scare you enough to use SPCS2022 as ground it should.
I thought I watched a NGS webinar 6 or 8 months ago where a viewer asked the NGS presenter if they'd still need to scale from the new state plane and the NGS guy said yes. Is that not the case? Or am I misunderstanding what you're saying here.
What Norm is saying is that the 2022 version will be closer to ground, hopefully for most applications, close enough. From what I've seen my burg with be OK. Like always, the Central Meridian of a TM zone will be the lowest point, it will rise up going east and west, so you may end up with the ellipsoid above ground in some areas and you'll have to shrink the grid distance to achieve ground. For lambert turn it 90d. The NGS presenter is correct, you'll still need to shrink or increase ground to get to the grid distances. It will be up to the surveyor to decide if it's worth it. If I'm within 40PPM, I doubt I'll even bother.
Very long thread here! We determine and set our Trimble scale factor on day 1 of any project, we set it and forget it. Never had any SF issues whatsoever working with all types of equipment including those used by the contractor when it goes to construction.
Very long thread here! We determine and set our Trimble scale factor on day 1 of any project, we set it and forget it. Never had any SF issues whatsoever working with all types of equipment including those used by the contractor when it goes to construction.
Same here, walk out of the office to the field and the projection is set, it never changes. It's not difficult to figure out what to use.