Kent McMillan, post: 428113, member: 3 wrote: I'll bite, what's a DAF? The larger point would be that on a project where the CSF varies considerably, If the Surface Distances were computed from Grid Distances using a project average CSF, that won't really express the relationship between Surface Distances and Grid Distances. What you end up annotating the map with are Surfaceish Distances.
On the other hand Grid Distances are unambiguous and independent of the heights of the stations at the endpoints of the line.
You have your terms incorrect, the formula I gave you will calculate a grid distance from the surface distance through the entire project by applying the datum adjustment factor of the project. It will not calculate the grid distance from the geodetic or the ground distance, nor will your formula calculate the surface distance. Your formula will only calculate a surfaceish distance.
Loyal, post: 428118, member: 228 wrote: I dunno Mighty, like you say, it's an "age old problem" (computer age that is).
There are many ways to DO IT, ALL of which have drawbacks.
I have a old project that re-emerges every few years, that covers ~40 sq. miles, and has nearly 6000 ft. of relief. Many years ago, I developed an LDP that has a developed (developable) surface of 10,000 NAVD88. There are points 2,000+ feet higher, and some 4,000 feet lower, but the "sweet spot" (where MOST of the activity was/is), stays within a few hundred feet (vertical) of the 10k contour.
Meta data is your only hope, record EXACTLY what you DID (right, wrong, close enough, whatever), and the next surveyor (assuming he/she isn't an idiot), will love you for it.
Loyal
It's not unusual to run into these projects. The first one I ever did with GPS had a bunch of relief, I was trying to set a 1/16th corner between a found section and 1/4 using the stakeout routine and it kept calculating it .2' off. I couldn't get my head wrapped around the fact that it was the elevation difference that was screwing me up. It was the 2nd or 3rd day I had the dang unit. I had done a calibration from some of my control, I quickly learned that maybe wasn't the best thing to do. Going from a 2d total station world to a 3d GPS world with lots of contours.
I did one with 2500' elevation differenc north to south for these same people starting in about 2001. I split the difference and created a surface about mid point, I was about .2' long in a mile on the low end and .2' short on the high end...........
My suggestions would be what you did in 2001 using an average elevation, or the elevation of the "important spot" on the ranch.
You've already mentioned using the PLSS Datum where the distances are reported at the average elevation of each line.
Geodetic mean bearing with distances at actual elevation always works, and with modern software any surveyor can rectrace/recreate it.
MightyMoe, post: 428120, member: 700 wrote: You have your terms incorrect, the formula I gave you will calculate a grid distance from the surface distance through the entire project by applying the datum adjustment factor of the project. It will not calculate the grid distance from the geodetic or the ground distance, nor will your formula calculate the surface distance. Your formula will only calculate a surfaceish distance.
Okay, you're in Wyoming, so I suppose that the term "Datum Adjustment Factor" has some meaning in Wyoming. Would it be this definition found in the Wyoming DOT Survey Manual:
"Datum adjustment factor: A dimensionless scale and elevation factor used to convert a distance between points on a state plane grid (state plane coordinates) to an equivalent distance between points on the ground (surface coordinates)."
In your example, where you were dealing with an elevation change of more than 1,000 ft. across the ranch in question, there obviously is no single scale factor that will serve as a one-size-fits-all "Datum Adjustment Factor" that will convert exact grid distances to Surface Distances at any other than some fictitious surface not at ground level through the project.
So, what's Plan B?
aliquot, post: 428136, member: 2486 wrote: Geodetic mean bearing with distances at actual elevation always works, and with modern software any surveyor can rectrace/recreate it.
I've considered that for years, maybe soon we will be doing that.
Gene Kooper, post: 428133, member: 9850 wrote: My suggestions would be what you did in 2001 using an average elevation, or the elevation of the "important spot" on the ranch.
You've already mentioned using the PLSS Datum where the distances are reported at the average elevation of each line.
I had to decide, this site is cool, after discussing it, it made up my mind and I've applied a DAF of 1.000285 making me long by about .15' in 10,000' along the East line and will be short on the west end where the property kicks up steeply. But the majority of the property will fit very well.
MightyMoe, post: 428157, member: 700 wrote: I had to decide, this site is cool, after discussing it, it made up my mind and I've applied a DAF of 1.000285 making me long by about .15' in 10,000' along the East line and will be short on the west end where the property kicks up steeply. But the majority of the property will fit very well.
So you used a project average CSF of 0.999715? Not exactly earth-shattering, but should we watch the stock market tomorrow just in case?
MightyMoe, post: 428121, member: 700 wrote: It's not unusual to run into these projects. The first one I ever did with GPS had a bunch of relief, I was trying to set a 1/16th corner between a found section and 1/4 using the stakeout routine and it kept calculating it .2' off. I couldn't get my head wrapped around the fact that it was the elevation difference that was screwing me up. It was the 2nd or 3rd day I had the dang unit. I had done a calibration from some of my control, I quickly learned that maybe wasn't the best thing to do. Going from a 2d total station world to a 3d GPS world with lots of contours.
I did one with 2500' elevation differenc north to south for these same people starting in about 2001. I split the difference and created a surface about mid point, I was about .2' long in a mile on the low end and .2' short on the high end...........
yeah.... Borkenhagen never told you about that, did he...? 😉
Rankin_File, post: 428166, member: 101 wrote: yeah.... Borkenhagen never told you about that, did he...? 😉
Slipped his mind till after, lol