I goofed up a bit (or maybe not at all depending on your viewpoint). I did a series of Auditor's Lot plats with all the field work being in unmodified state plane grid. The general practice in this state is to take the grid and apply a DOT scale factor to give you ground coordinates & distances. That's the only modification. I drew up the surveys for recording, got to the end, and realized all my drawings and comps are straight SP Grid. I put a very clear note of this on the drawings and said something like "distances shown are grid distances" and "bearings are referenced to state plane grid north, etc.". So that everyone knows how I did it and the conversion factors.
Now, after I realize my goof, and having recorded a couple surveys showing GRID measurements, I'm doing another one in the same area, but not adjoining the other ones I did. Is it worthwhile to convert my base map for those 6 sections so that everything can be shown in ground distances? Is it even a big deal that everything is shown in grid distances considering I clearly state what the distances are on the face of the survey, which will be recorded? Outside opinions needed.
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?
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).
Are you using Grid Areas?
Also an important part of metadata. On that note, remember that area is a linear unit squared, so the CSF is squared for area scaling.
What are Auditors Lot plans?
lmbrls, post: 385885, member: 6823 wrote: Are you using Grid Areas?
If "Auditors Lot Plats" are used to calculate areas for taxation purposes you may be in for interesting times...
IMHO grid data should only be used on engineering surveys, NEVER on anything dealing with boundaries.
Csf = 1/ (sfXef)
where Combined Scale Factor = 1/ (Scale factor times Elevation Factor)
Now a days, javad software gives me csf and theta on anything i have a coord on.
I've had to do some boundary work in State Plane, it was a PITA, all the areas didn't match with the geometry, kept getting questioned about it.......
Hope I never have to do it again.
But you didn't do anything wrong, I would not continue it however, just my 2 cents.
I would switch now and not look back, explain it on the next set of plats.
Grid distances (along with areas computed from them) do not reflect the reality that the public expects. When someone is paying for land at a negotiated price per acre, those acres need to be true, not on some imaginary plane created for mathematical convenience.
Bow Tie Surveyor, post: 385899, member: 6939 wrote: Grid distances (along with areas computed from them) do not reflect the reality that the public expects. When someone is paying for land at a negotiated price per acre, those acres need to be true, not on some imaginary plane created for mathematical convenience.
Agreed. Slapping a statement on the survey that distances shown are grid distances might have covered your butt, but you arent doing anyone any favors. Most people just don't understand the difference.
It's something that adds value to being a Professional Surveyor. The computations aren't that hard for a licensed professional, it's math. Most people can't read an engineering or architectural plan for their house and I don't see them worrying. Working in grid is easier sometimes, especially on larger boundary projects with GPS or GIS involved and for many engineering projects. We do about half and half but most larger projects are in grid, at least for cad and comps. Sometimes we label the ground distance (easy civil3d style) for the paper/pdf prints, sometimes its all grid. Depends on the client requirements followed by our professional experience. As long as we ensure everything is well noted, use whatever you want based on your professional judgment.
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Nate The Surveyor, post: 385891, member: 291 wrote: Csf = 1/ (sfXef)
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.)
I think we sometimes forget that we are preparing surveys for the public and not each other. We are required in GA to show horizontal distances and areas. This can make a significant difference when the property is valued at $40 a S.F. I show distances as horizontal and coordinates as SP. A note stating this and the C.G.F. is placed on the survey. Our DOT shows grid areas on Right of Way Plans without stating this fact. This has caused several telephone conferences with high dollar attorneys resolving alleged area discrepancies.
Speaking of area...I have seen plats that have areas to the fraction of a sq ft. I think what many people don't realize is the uncertainty in the computation of areas. Assume for simplicity that you have a 1000' X 1000' tract. If the distances are å±0.05', then the computed area can vary from 999,900 sq ft to 1,000,100 sq ft, an uncertainty of 200 sq ft. We have all seen deed distances that have been in error by feet, so really the uncertainty in area is usually much larger. Even on a 100' X 100' lot, an uncertainty of 0.02' results in an area ranging from 9996 to 10004, a difference of 8 sq ft. So why do surveyors quote areas to fractions of a sq ft?
John Hamilton, post: 385940, member: 640 wrote: Speaking of area...I have seen plats that have areas to the fraction of a sq ft. I think what many people don't realize is the uncertainty in the computation of areas. Assume for simplicity that you have a 1000' X 1000' tract. If the distances are å±0.05', then the computed area can vary from 999,900 sq ft to 1,000,100 sq ft, an uncertainty of 200 sq ft. We have all seen deed distances that have been in error by feet, so really the uncertainty in area is usually much larger. Even on a 100' X 100' lot, an uncertainty of 0.02' results in an area ranging from 9996 to 10004, a difference of 8 sq ft. So why do surveyors quote areas to fractions of a sq ft?
They set their CAD software to show areas to the nearest hundredth (hundredth of anything). I bet if you looked @ areas those same surveyors published in acres you would also see those to the hundredth of an acre which would be +/- 43 square feet? Surveyors more than most should have a strong knowledge in significant digits.
On similar note, when most of us publish a legal description, we use distances to the nearest hundredth of a foot, and bearings to the nearest second. That doesn't bother me, even if our theoretical precision in each measurement might not be that precise. By the same token, I have no problem publishing square feet to the nearest square foot. That is more precise than the measurements most likely...but it is the area of the described parcel.
Yes, if you publish sq ft then I agree it has to be to the nearest square foot, but decimals of sq ft?
I saw once a treatise in a textbook on uncertainties in area computations, but I cannot find it at the moment. It would be nice to have a program that would compute that, based on inputting coordinates and error ellipses.
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.)
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.
Allen Wrench, post: 385877, member: 6172 wrote: I goofed up a bit (or maybe not at all depending on your viewpoint). I did a series of Auditor's Lot plats with all the field work being in unmodified state plane grid. The general practice in this state is to take the grid and apply a DOT scale factor to give you ground coordinates & distances. That's the only modification. I drew up the surveys for recording, got to the end, and realized all my drawings and comps are straight SP Grid. I put a very clear note of this on the drawings and said something like "distances shown are grid distances" and "bearings are referenced to state plane grid north, etc.". So that everyone knows how I did it and the conversion factors.
Now, after I realize my goof, and having recorded a couple surveys showing GRID measurements, I'm doing another one in the same area, but not adjoining the other ones I did. Is it worthwhile to convert my base map for those 6 sections so that everything can be shown in ground distances? Is it even a big deal that everything is shown in grid distances considering I clearly state what the distances are on the face of the survey, which will be recorded? Outside opinions needed.
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?
John Hamilton, post: 385940, member: 640 wrote: So why do surveyors quote areas to fractions of a sq ft?
Because they are very precise button pushers.
