The RTK surveys and DAF's

The important part is publishing what you did to the data. How was the DAF applied? I realize the name should be a clue, but commonly used nomenclature varies dramatically around the world. Beating your chest and proclaiming you are correct (even if you are) won't get the job done. Communicate the math and science behind the tools. The response is usually positive.

I'll bite: what's a DAF?

Huh??

DAF is the datum adjustment factor used to bring state plane distances to surface or ground distances. The term seems to have originated with DOTs.

Also called PAF or project adjustment factor.

I would call that CSF, combined scale factor.

Those are those pesky little numbers that as surveyors we can absorb and feel good about because they are within tolerance.

They are also those little things that title companies and attorneys fault surveyors at in attempting to change the record.

|-)

I've heard about those kinda title companies, we don't seem to be afflicted with them out here

MightyMoe, post: 347589, member: 700 wrote: Huh??

In a perfect world, adjustments to ground are accomplished by scaling the distances. Being practical creatures we see the assignment of a DAF usually matches ground to meet our needs. There are several schools of thought on how to apply it. We can use it directly when projecting from geographic, apply to whole ordinates or apply to distances (in essence scaling from a specific point).
My admonition was not necessarily directed at you personally. My observation of the profession is most tend to describe their choice as THE correct way. The problems this creates are exacerbated by refusal to state meta data because 'the stupid end user should know what to do'.
If we understand what to do (and communicate our choices) it makes things better all around. Picking apart the way others treat data or demanding acceptance of our way as the sole correct method does nobody any favors.

MightyMoe, post: 347590, member: 700 wrote: DAF is the datum adjustment factor used to bring state plane distances to surface or ground distances. The term seems to have originated with DOTs.

Also called PAF or project adjustment factor.

I don't really work with GPS or state planes. However I do own a GPS used for elevations.

But I must ask, if I want to locate something in state plane, my GPS is RTK going through a CORS network.

Wouldn't this then already be converted down to a grid distance in my collector?

And when finding a SPC loaded into the collector, wouldn't the RTK then convert to ground when staking?

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You are welcome to tell the other surveyor that, it's on his plat.

The idea was to disconnect the number from scale factors which are usually thought of as a number applied to the ground distance to get to state plane distance.

I think Trimble calls it a ground scale factor, if I remember correctly.

I've also see it called a combined scale factor as you pointed out.

I usually think of the combined factors as a number like 0.9997 while the DAF will be the reverse or 1.0003.

It really is only tenuously related to the scale factor since it tries to mean the grid to ground distance number across a large area, so it really isn't calculated at one point, but is a best fit for many points.

MightyMoe, post: 347590, member: 700 wrote: DAF is the datum adjustment factor used to bring state plane distances to surface or ground distances. The term seems to have originated with DOTs.

Ah, I didn't recognize the generalized form. I'm more familiar with the specialized version, the Datum Adjustment Factor For Yesterday's Datum Uniformly Collected Kinematically.

Ok,,,,,,,,,,,,,you do realize that I'm discussing two OTHER surveyors (well one surveyor and one engineer) who both surveyed a section, completely unrelated to ANYTHING I'm doing besides reviewing the results. AND I'm showing what a good job they BOTH did.

In fact the engineer brought in photos of all the monuments, he located them twice just like I've asked him to, and he is a very good surveyor, I can't imagine anyone I would rather have topo and design a site or road. Or stake one, he really knows his stuff.

The DAF issue is just relating that while they both came up with different numbers it doesn't disregard ANYTHING they BOTH did, nor does it make either survey different in any meaningful way.

The extra long DAF is an unnecessary computer generated number that he doesn't do anymore, cause he got tired of messing with it, as you can see the surveyor already knew better.

I honestly don't know.

It depends how your Data Collector is set up, to get state plane coordinates out of mine I must first set the job up I'm in as a state plane job.

However if it's in state plane then everything I'm doing is state plane, the distances will be "on the grid" in my case about 2.5' to 4' per 10,000' shorter than measuring along the ground.

If I want ground coordinates or ground distances I will either have to get out of state plane or tell my DC to "modify" state plane by a factor. There are many ways to do it, they all have pluses and minuses.

Jim, it's really a made up thing, the first time I used one was back in the late 70's, they had one for the whole county and it was 1.0003, for some reason they called it the Pryor factor.

It actually worked pretty good on the west side of the county, not so good on the east side. Of course it was all NAD27 and there were more issues with accuracy than the scale factor

MightyMoe, post: 347617, member: 700 wrote: I honestly don't know.

It depends how your Data Collector is set up, to get state plane coordinates out of mine I must first set the job up I'm in as a state plane job.

However if it's in state plane then everything I'm doing is state plane, the distances will be "on the grid" in my case about 2.5' to 4' per 10,000' shorter than measuring along the ground.

If I want ground coordinates or ground distances I will either have to get out of state plane or tell my DC to "modify" state plane by a factor. There are many ways to do it, they all have pluses and minuses.

I'm guessing so then. When I set up the job I tell it what zone I'm in and I'm pretty sure the scale factor as well although I would have to check

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Jim,

Be nice.

MightyMoe, post: 347611, member: 700 wrote: The idea was to disconnect the number from scale factors which are usually thought of as a number applied to the ground distance to get to state plane distance.

I think Trimble calls it a ground scale factor, if I remember correctly.

I've also see it called a combined scale factor as you pointed out.

I usually think of the combined factors as a number like 0.9997 while the DAF will be the reverse or 1.0003.

It really is only tenuously related to the scale factor since it tries to mean the grid to ground distance number across a large area, so it really isn't calculated at one point, but is a best fit for many points.

CSF * ground = grid

Star*Net gives you the option of calculating the CSF as an average over the project or at a specific point. You can even hand-enter a CSF, for those who like to roll their own.

Aka the DAFFY DUCK

Yes and DAF * grid=ground