Scale Factor

Scale factor or combined factor or project factor. Also what is your false northing and easting. I usually carry out to 8 or 9 places. On combined factor for coordinates .

As an experiment; take a job you've done with a limit of 1/4 of a section that uses one of your 9 place project factors applied to state plane distances to get ground distances between points. Put a state plane coordinate on the NE corner of the area. Now take the state plane coordinate on the NE corner and recalculate through the job but only using the scale factor applied to the distances rounded to 6 places. Tell me the differences to .01' of the resulting coordinate values. For this project it would be necessary to (off the top of my head) extend out over 7 miles before coordinate differences of .01' would begin to show up.

DOT is funny. Back in the good old days, 1960s-1970s the old timers would run state plane coordinates all over the ROWs and they developed regional project factors. The one locally was called Pryor and it was 1.0003. Then they got nerdy and decided to get "real" project factors and started to restrict the area of each factor and publish them to 9 places. How they come up with one of those is ,,,,,,,,,,,,amusing.

To us old guys that calculated mountains of state plane coordinates by hand I believe we had way better handle on how the math actually works (the grid factors in the state plane books were only published to 6 places). 1.0003 was too sloppy, but 9 places is 1ppb and is unnecessary for any work. 6 places is 1ppm and is impossible to measure using standard field techniques. But 6 places is the "sweet spot" that can make you feel warm and fuzzy. So we usually use 6 place project factors.

A project factor is not a combined factor, it's used to convert (as a reverse) grid distances to surface distances moved up above the state plane surface to simulate ground distances. If I inverse across my site I get a surface grid distance of 3713.06' and a ground distance of 3713.04'. State plane distance would be 3711.92' using 1.000308 or using 1.0003077650 it would be 3711.92'.

Ain't reality fun?

More people need to get a grip on reality. Saw a subdivision earlier this week that had lot lines like 209.7682 feet.

That's a good one.

Our published subdivision labels of 1 second and .01' for everything is a fantasy already; there's no need to make up imaginary numbers.

Saw a subdivision earlier this week that had lot lines like 209.7682 feet.

That's probably just a sloppy precision setting in cad and they're not actually claiming to measure that; I think the default setting is 4 decimal places.

When you publish your work i.e. a subdivision plat, your are claiming that information shown to be true. If your are not going to claim 267.2589 then don't publish to the 4th decimal place.

The great Paul Reid advised me many years ago that the words true, correct, accurate should never make it into a surveyor's statement.

When you publish your work i.e. a subdivision plat, your are claiming that information shown to be true. If your are not going to claim 267.2589 then don’t publish to the 4th decimal place.

I hope not. If that is the case then every surveyor I have ever known is a liar. We report to a certain precision by convention, not by significant digits. Back in the day, perhaps some did use significant digits, but it is no longer allowed.

I remember high school math, and I can assure you no one uses significant digits on their surveys, at least not on plats that are reviewed by planners. Try putting distances to the nearest foot and 10 feet on a plat, and see what happens.

When look on a survey and you see 89.98 feet for measurement, that it is not making an an accuracy statement.

Should it? That is a discussion we can have, but I can promise you that it does not mean it at this point in our history.

Our published subdivision labels of 1 second and .01′ for everything is a fantasy already; there’s no need to make up imaginary numbers.

Had a bearing on a line to like 3 decimal places of a second on a survey I was looking at. It made no sense, until I realized it was far enough away that the relative accuracy of my GNSS observations would notice anything less. No other measurement on the map had that precision, and when I got through, I realized that by doing so when I searched for the points I hit them with the expected distances. It was the one time I did not think it was useless.

I can agree with that for scaling distances. Unfortunately I am not in a PLS state and here we and I don’t like it scale coordinates. So that changes things. I am a firm believer in scaling the distance vs coordinates. Which is how it should be. Reduce ground distance to ellipsoid or mean sea level depending on datum. Then to grid. But it can all be done at once as well. Some is muscle memory also from doing this in different parts of the world on UTM in the military and yes all by hand including all angles distances reduced. Pulling the scale factor from tables computing the elevation factor then any other factor that was needed. No software for those grid traverse period. Convert lat long to easting northings. At different spots along the route. Of course all that was meters and then elevation had to always be placed in feet mostly international foot as we were not in conus. I could probably dig up some old DMA forms we had to log everything into.

I do see your point though. I was just asking a question.

I'm with ya old man. The idea that I'm expected to enter that number in one field in TBC and CAD to make scale coordinates useful is just too much. I'm going to tell the senior mappers, surveyors and engineers that scaled coordinates must stop and soon (according to some surveyors). We need to survey (in my areas) at least a mile underground from now on for all road projects (as it's been expertly explained to me). Just because all the volumes, areas, length of bridges and ROW widths need to be constantly corrected is irrelevant. What's important is that the survey tech doesn't need to think far enough to enter that one number.

And to prove my selflessness I will continue to keep doing those jobs. I'll be sure to tell them that surveyors like you will never, never lower themselves to work like they want. I'm taking that awful blow for team State Plane.

State Plane forever!!!!

In fact, I should organize a group of like-minded to officially boycott working with them, maybe a signed doc from all of them.

I know what I'm doing is rough. They actually make me wait sometimes almost a week after I submit a bill before the money appears in my bank.

They don't even send me a check!!!!!!!

I have to look at the notification on email.

Imagine the horror.

You can thank me later.

Well it is tough. My geodetic side and the survey side are always in a battle. But the reading of old NGS publications and old Letters they published makes me feel a little better. Because they all had the same arguments LOL. The main thing is we have many ways mathematically to achieve the same goals it truly boils down to understanding and knowing when a one point scale coordinates works and does not work on a particular site for sure. I often have to use the TBC. But what I usually do is look at the scale factor the elev factor and combined factor around the site from the points list and the average ellipsoid height on nad 83 to come up with the best solution for that situation. Just grabbing a point and say well ok this is it sometimes can cause more harm than not. But those are those unusual sites where the scale in a lambert can be north south and flip and or the huge elevation changes on a given site that also can throw a wrench.

I do have to ask. The “Pryor” you mentioned above was that named for the Mr Pryor who was a member of the Buro of roads on ROW surveys etc. he published an article I have never been able to find about the method you utilize I believe and he and that method were mentioned in a old publication from NGS about that very topic. I can’t remember all the details but I remember it was in one where NGS was discussing and showing how to do all the math and even showed Mr pryor’s method and how that worked as well. I bet it was for nad27 as the formulas had to all do with sea level and such.

I don't know where that name came from or even if the spelling is correct, it's been over 40 years since I looked at those data sheets.

I assume it's from a local geographic feature and not someone's name.

I knew that name had a historical connection, Sergeant Nathaniel Pryor, you can look it up on google to get the story.