squowse, post: 385957, member: 7109 wrote: I was wondering if there is a standard for whether csf = grid distance / ground distance and vice versa.
I am sure I have seen it both ways round. We don't use many scale factors here so easy to check each time.Star*net uses CSF = grid / ground I think.
Definitions I've seen define the Combined scale factor as "Grid Scale factor" * "Ellipse Height Scale factor". But I think I've seen more people call the inverse of that as being the CSF.
One publication training I saw use the CSF as GSF*HSF and the inverse of that they called the "Ground Scale Factor" But that's can be scary if you abbreviate both The Ground SF and the Grid SF as GSF.
My opinion, which I know won't catch on' is that you should leave the CSF as what it is defined to be and either multiply by it to take ground distance to a grid distance, and Divide by it if you are going the other way so there is less confusion as to which number you are using.
i would also use clear terminology such as not calling one of them just the "scale factor" it is a Grid, or a Height or a combined or 1/Combined Scale factors.
In my state the CSF is always a number with three nines behind the decimal (0.999#####) and the inverse of that is always greater than one with three zeros behind the decimal. So I can tell....but I think it should be more clearly defined.
Jim Frame, post: 385929, member: 10 wrote: That's not the way I'm accustomed to calculating CSF. I think SF*EF is more typical. (That's the way Star*Net does it.)
Long ago several vendors began (incorrectly) referring to 1/csf as 'scale factor' or 'combined scale factor'. You can sometimes tell what brand gps a person uses by the terminology they use.
It used to give me a headache. I'm better at ignoring g it now, unless of course somebody mentions it (sending me on a rant)...o_O
squowse, post: 385957, member: 7109 wrote: Star*net uses CSF = grid / ground I think.
I used to refer to the combined factor as "combined scale factor" or "CSF", but now I call it simply "combined factor". "Combined Scale Factor" implies that the number is a combination of scale factors. Typically "Scale Factor" refers to the Grid Factor. This is the distortion caused by the separation of the ellipsoid from the grid surface. The Elevation Factor is the distortion caused by the separation of a point on the Earth surface and the ellipsoid.
The Combined Factor is:
EF x GF
or
EF x SF
depending on your preference for the Grid Factor terminology.
The Combined Factor, when multiplied times the horizontal surface distance (ground), produces the grid distance.
Taking the reciprocal of the CF produces what is sometimes referred to as the "Grid to Ground factor". It's not really a formal term, but is useful. Multiplying a grid inverse distance times the Grid to Ground factor (or 1/CF) produces the ground distance.
These discussions continue to make me think we should all be pushing for low distortion projections for the next reference frame from NGS (2022).
Tom Adams, post: 385960, member: 7285 wrote: Definitions I've seen define the Combined scale factor as "Grid Scale factor" * "Ellipse Height Scale factor". But I think I've seen more people call the inverse of that as being the CSF.
One publication training I saw use the CSF as GSF*HSF and the inverse of that they called the "Ground Scale Factor" But that's can be scary if you abbreviate both The Ground SF and the Grid SF as GSF.
My opinion, which I know won't catch on' is that you should leave the CSF as what it is defined to be and either multiply by it to take ground distance to a grid distance, and Divide by it if you are going the other way so there is less confusion as to which number you are using.
i would also use clear terminology such as not calling one of them just the "scale factor" it is a Grid, or a Height or a combined or 1/Combined Scale factors.
In my state the CSF is always a number with three nines behind the decimal (0.999#####) and the inverse of that is always greater than one with three zeros behind the decimal. So I can tell....but I think it should be more clearly defined.
The difference goes way back to the days people did state plane by hand.
The CSF was used to multiply the measured surface distance to calculate the Grid distance, this was important to have to calculate all the traverse lines.
Since no one wished to work in state plane, the Surface Adjustment Factor (SAF) or Datum Adjustment Factor (DAF) was developed. This was a single factor to apply to an area and is usually expressed as larger than one.
It is applied to existing state plane coordinates to "raise" the area to "surface" or a close approximation.
The CSF is only valid for one point or one line, each point and each line has a unique CSF. The DAF is applied to all coordinates and lines in a project area, thus simulating ground distances, although each distance will still have an error, if you can get that error under a few ppms it means you have a flat small site.
I've always assumed they have been expressed the way they are generally seen to avoid confusion, for me it works.
I can look at an old set of DOT plans from the 1970's, see the 1.0003 factor and know what it means.
Shawn Billings, post: 385966, member: 6521 wrote: I used to refer to the combined factor as "combined scale factor" or "CSF", but now I call it simply "combined factor". "Combined Scale Factor" implies that the number is a combination of scale factors. Typically "Scale Factor" refers to the Grid Factor. This is the distortion caused by the separation of the ellipsoid from the grid surface. The Elevation Factor is the distortion caused by the separation of a point on the Earth surface and the ellipsoid.
The Combined Factor is:
EF x GF
or
EF x SF
depending on your preference for the Grid Factor terminology.The Combined Factor, when multiplied times the horizontal surface distance (ground), produces the grid distance.
Taking the reciprocal of the CF produces what is sometimes referred to as the "Grid to Ground factor". It's not really a formal term, but is useful. Multiplying a grid inverse distance times the Grid to Ground factor (or 1/CF) produces the ground distance.
These discussions continue to make me think we should all be pushing for low distortion projections for the next reference frame from NGS (2022).
Low distortion or not, you need to state your Scalar factors (please correct me if I'm wrong). I disagree with calling one of them simply Scale Factor, since they are all "scale factors". The Grid SF is a grid-ellipsoid factor, and the Elevation Scale Factor is a Scale Factor as well. Even the term "Elevation" is ambiguous as many guys think that implies the orthometric height. Using GSF isn't that many more letters than SF. or it should just be spelled out.
Sorry, about the semantics here, but this stuff is widely misunderstood and partly because of terminology.
And don't get me started on "Grid Coordinates". It seems like Trimble uses the term for cartesion coordinates @ Ground level. A lot of guys say "Grid Coordinates" as a short-form for State Plane Grid. Maybe Trimble, the NGS you and I all need to be more clear. It's hard enough for many guys to get the concepts and it doesn't help with we have different ambiguous terms we use.
MightyMoe, post: 385968, member: 700 wrote: The difference goes way back to the days people did state plane by hand.
The CSF was used to multiply the measured surface distance to calculate the Grid distance, this was important to have to calculate all the traverse lines.Since no one wished to work in state plane, the Surface Adjustment Factor (SAF) or Datum Adjustment Factor (DAF) was developed. This was a single factor to apply to an area and is usually expressed as larger than one.
It is applied to existing state plane coordinates to "raise" the area to "surface" or a close approximation.The CSF is only valid for one point or one line, each point and each line has a unique CSF. The DAF is applied to all coordinates and lines in a project area, thus simulating ground distances, although each distance will still have an error, if you can get that error under a few ppms it means you have a flat small site.
I've always assumed they have been expressed the way they are generally seen to avoid confusion, for me it works.
I can look at an old set of DOT plans from the 1970's, see the 1.0003 factor and know what it means.
I get the history. 1.003 is only a factor you would get in higher elevations. for some lower-elevation states, you would need to be very clear which factor you are publishing. (or maybe not....if you're that close maybe you just use a factor of 1.0000)
My understanding is that in formal parlance "Scale Factor" always refers to the Grid Factor (ellipsoid to projection surface). You'll note that Jim's screen shot from Star Net uses the same terminology. I'll be happy to change if you provide an authoritative source. For now, I'll continue to consider the Scale Factor to be synonymous with the Grid Factor.
The Grid is the Grid regardless of which Grid to which we refer. If the Grid is from low distortion or State Plane, it's still the grid. It's probably better form to provide the combined factor even for a low distortion projection, however, the idea of an LDP is that the combined distortion from scale and elevation are of such a small degree as to be considered negligible.
I do think it is important to be precise in our language and I appreciate what you are saying, Tom.
I used to refer to 3D plane coordinates and NEZ. Dave Doyle wrote an article regarding the proper use of "Z" in coordinates. XYZ is reserved for Earth Centered Earth Fixed systems. The more appropriate designation is U for Up unless the height is specified as an Orthometric Height (H) or Ellipsoid Height (h). It made sense, so I've referred to plane coordinate components as NEU ever since.
Tom Adams, post: 385971, member: 7285 wrote: ...since they are all "scale factors"
NGS data sheets list "Scale Factor", "Elevation Factor", and "Combined Factor" for a reason. The elevation factor and the combined factor are not technically scale factors.
The scale factor for any point on any state plane coordinate system can be calculated given only the projection's parameters and the position of the point, either as lat/lon or state plane coordinates. That's because scale is a pure mathematics term and the relationship between an ellipsoid and a state plane coordinate system is pure mathematics. Scale is mathematically defined.
Elevations, on the other hand, do not vary with position in a functional way. Given only its coordinates and state plane projection parameters, it is not possible to calculate the elevation factor for a point. Elevation factors, then, are not scale factors.
Combined factors, being the product of scale and non-scale factors, are not scale factors, either.
If you want to be absolutely technically correct, then only one of the factors is a scale factor. But the terms "Elevation Scale Factor" and "Combined Scale Factor" are so firmly entrenched that they will likely continue on into eternity.
Tom Adams, post: 385971, member: 7285 wrote: Low distortion or not, you need to state your Scalar factors (please correct me if I'm wrong). I disagree with calling one of them simply Scale Factor, since they are all "scale factors". The Grid SF is a grid-ellipsoid factor, and the Elevation Scale Factor is a Scale Factor as well. Even the term "Elevation" is ambiguous as many guys think that implies the orthometric height. Using GSF isn't that many more letters than SF. or it should just be spelled out.
Sorry, about the semantics here, but this stuff is widely misunderstood and partly because of terminology.
And don't get me started on "Grid Coordinates". It seems like Trimble uses the term for cartesion coordinates @ Ground level. A lot of guys say "Grid Coordinates" as a short-form for State Plane Grid. Maybe Trimble, the NGS you and I all need to be more clear. It's hard enough for many guys to get the concepts and it doesn't help with we have different ambiguous terms we use.
I agree, using the term grid to mean State plane coordinate systems isn't very useful......
We all pretty much only survey in grid, even if it's a lot survey and plunk a total station on the southeast corner, look at the northeast corner and set zero for the azimuth, you are creating a grid.
Frankly the term grid seems to be something new, I see it here on this site but never in the real world do I hear surveyors use it that way.
So many acronyms meaning so many different things just add to the confusion
MightyMoe, post: 386005, member: 700 wrote: I agree, using the term grid to mean State plane coordinate systems isn't very useful......
We all pretty much only survey in grid, even if it's a lot survey and plunk a total station on the southeast corner, look at the northeast corner and set zero for the azimuth, you are creating a grid.
Frankly the term grid seems to be something new, I see it here on this site but never in the real world do I hear surveyors use it that way.
So many acronyms meaning so many different things just add to the confusion
I can see the logic behind differentiating between Cartesian coordinates being called "grid" coordinates, and Latitude/Longitude being spherical coordinates, but it does get confusing when a lot of guys refer to SPG coordinates as simply "grid"
MathTeacher, post: 386001, member: 7674 wrote: NGS data sheets list "Scale Factor", "Elevation Factor", and "Combined Factor" for a reason. The elevation factor and the combined factor are not technically scale factors.
The scale factor for any point on any state plane coordinate system can be calculated given only the projection's parameters and the position of the point, either as lat/lon or state plane coordinates. That's because scale is a pure mathematics term and the relationship between an ellipsoid and a state plane coordinate system is pure mathematics. Scale is mathematically defined.
Elevations, on the other hand, do not vary with position in a functional way. Given only its coordinates and state plane projection parameters, it is not possible to calculate the elevation factor for a point. Elevation factors, then, are not scale factors.
Combined factors, being the product of scale and non-scale factors, are not scale factors, either.
If you want to be absolutely technically correct, then only one of the factors is a scale factor. But the terms "Elevation Scale Factor" and "Combined Scale Factor" are so firmly entrenched that they will likely continue on into eternity.
Thank you Teacher. I can understand that you can't have an elevation scale factor for a point, but you can for a line....and it is mathematically determined, isn't it? But I can accept that the more appropriate terms might be "Scale Factor", "Elevation Factor", and "Combined Factor"; and if that is how they say it on the NGS data sheets, then I humbly surrender to those terms.
Speaking of combined factors: to carry higher precision in your calcs going from grid back to ground, especially if working with large distances or coordinates, always divide by the chosen combined factor (rather than use the rounded off reciprocal of the combined factor). Is there any reason to ever calc or use the reciprocal?
Tom Adams, post: 386009, member: 7285 wrote: ...and if that is how they say it on the NGS data sheets, ...
Thinking about it further, there is an element of context here. When you calculate one combined factor for an entire area and adjust the coordinates of points with that factor, you are, to some degree, changing the length of the mapping radius of the projection. It isn't perfect because scale factors change continuously over a projection and this approach assigns the same factor to every point. But it obviously works quite well.
To that extent, there is wisdom in calling that factor a "Combined Scale Factor."
The NGS context assigns individual factors to individual points, so "Combined Factor" is appropriate. But, "Combined Scale Factor" is not that inappropriate in the context of an overall adjustment to coordinates in a particular area.
So, maybe everybody's right, huh?
BajaOR, post: 386015, member: 9139 wrote: .... Is there any reason to ever calc or use the reciprocal?
In my first job out of college, I used a Monroe electric rotary calculator. If you've ever used one of those with an eight-digit divisor, or done long division by hand with an eight-digit divisor, then you appreciate the convenience of reciprocals.
I wonder if reciprocals in current workflows are a carryover from those days. Perhaps it was easier to program what people were used to doing than to introduce a new concept. Once it was done, changing it became even harder.
Someone above said that you could determine the equipment used by the factors used. Are there widespread differences?
Oh good lord, this certainly blew up on me after taking one day off. I'll respond to the posts above but the main premise is that I regret doing it this way, but I was so far into it that I didn't want to introduce confusion by changing all my coordinates and base maps. The main question is, if you found a recorded plat of a lot and the notes said right on it that all distances are grid, and here's the ground scale factor, could you deal with that?
yes.
BajaOR, post: 385883, member: 9139 wrote: Once a project is on grid, leave it on grid. If you do and leave all your work on grid, it's all tied together. Is there a rule that you must use ground distances and astronomic or geodetic bearings?
No rule stating what system the bearings or distances must be on. I just kept it all on grid because I was dropping in some GIS stuff in the early stages and it made things easier keeping it in grid and having one less conversion to do. I don't know what I was thinking - that's not my normal procedure. Never again!
Shawn Billings, post: 385884, member: 6521 wrote: Unless your State has some specific statutes that prevent it, you probably have a lot of leeway in how you document your surveys. The important, make that CRITICAL, thing is that you clearly document in your metadata to what the distances and directions are related, which it sounds like you did. (Kudos for that!).
For extra points give a little instruction that tells how to convert what you are providing to the other common format. For instance: Distances are expressed in (units), as measured along the Grid for the (State Plane System), to convert reported distances to distances measured horizontally along the surface of the Earth, divide reported distances by the project combined factor of (CF).
Yes, I always have a note on every survey (if it happens to be in grid) that says something like "Grid distances are shown and are in terms of International Feet. Multiply distances by a scale factor of 1.0002345454 to derive ground distances..." and "Bearings are referenced to grid north [YOUR STATE] state plane coordinates". That way any competent surveyor can pick up my drawing and know how to convert, if necessary.
Tom Adams, post: 385958, member: 7285 wrote: I don't know what you mean by a "DOT" scale factor....what's that? do you mean a combined scale factor for your local survey, or does the DOT assign a scale factor for your whole state? I assume DOT would be the State DOT maybe, or some counties might have their own Dept. of Transportation.
My more important question is, does it affect the area of your parcels, and/or is it on your contract to apply the DOT scale factor. What is your elevation? Does a scale factor even affect your distances? One problem you might have is whoever contracted you to do a job for them might hold you to some standard (if there is one). If it's in your contract, you may need to eat the error and make it right. If it is not, you might want to approach them and mention that you did not apply a factor, and is that okay with them, or would they like you to portray your information in another format? Decide if you "screwed up" or not and act accordingly. Are you publishing areas based on your measurements or are they using the deeded areas or the assessors areas for their evaluation?
The DOT scale factor is a combination factor (some sort of best-fit factor) assigned to each county in the state. You simply multiply that factor by the grid distances to get ground - no other modifications are made. In this case the lots are small enough that the difference in areas is negligible. Grid vs Ground in this county about 0.6' per mile.
