I've posted this question a long time ago on the more open forum.

I'm posting it here/now because I know here virtually all posters will be GPS users.

Do you use SPC coordinates exclusively on your surveys?

The biggest headache I have is deciding to, or not to report my data in SPC. I can't see a good reason for using GPS, getting SPC, then BASTARDIZING that good data.

By the same token, I can't see any good reason to keep GPS in SPC then using GROUND measurments for everything else(that is using measurements most everyone can understand)

I'm lucky, in my area the combined contant is about 0.99995-0.99997 and I can use SPC and kinda ignore the intigracies of SPC.

The people who check my legals and maps don't understand surveying and try as I may, they REALLY don't understand SPC's even though we've got a brand new GIS system based on SPC's.

You might be amazed at how much confusion there is about datums, coordinate systems, and map projections even among very talented people. This confusion is not limited to surveyors. It also extends to those who manage GIS maps and those who write the software we use to make the measurements and create the map information.

Please do not think I am painting everybody with the same brush. I have learned as much about coordinates in this century, with some prodding from Mr. Geodesist and Dave Doyle, as I learned in the previous three decades. But I know that when I started my most recent learning exercise I knew more about it than some of the doctors of geography or surveying that I have met.

We should not expect a university education to cure this defect when those who teach have yet to figure it all out.

I still do not claim to be a geodesist, probably never will be, but I am beginning to really get it.

I am also beginning to understand why survey work that is not connected to the geodetic network will someday be useless.

We should be relating all of our survey work to the National Spatial Reference System as an aid to retracement. We should have plans in place to move our digital maps to whatever place the NSRS goes. That should particularly apply to federal agencies but it ought also to apply to all public records including tax maps and public utility maps.

http://www.ngs.noaa.gov/PUBS_LIB/develop_NSRS.html

If one of you guys will help me out by turning that into a link I would appreciate it.

One thing we lack in our efforts to relate our work to the NSRS is GIS, CAD, and COGO software that will compute ground values from grid coordinates. We need the grid coordinates to be able to plot positions on our maps and to relate those maps one to another in the GIS. We need ground distances, areas, and volumes to be used for data input and output so our survey tradition of reporting these things as what we MEASURED can continue.

As some folks on this message board like to say... This would be EASY to do in the COGO, CAD, and GIS software if the companies who write the software would add the tools. They like to tell me that there is no market for such tools.

Speaking of which, in order to put ground coordinates on a geodetic system, we need a program that recognizes that geodetic system.

AKA GEOID03?

I did some cross checking this week, GEOID99 to GEOID03 and have had up to 0.02' differences in the areas of my projects. There are areas out there with a lot more or they would not have done it. For now we will check the area difference and pretty much ignore changes within our tolerances.

Paul in PA

Yes, I am beginning my third year of business and got 3 Promarks now. I want all of my major projects to be on the State Plane coord system. This may seem stupid to some people, but, I'm just wondering what you guys do as far as the actual drawing environment goes. Is your AutoCAD drawing on the grid or has it been brought up to ground? I would think you would want it to be on the grid, but, what happens when I give a "grid" drawing or description to an engineer or title company and the distances are a little smaller than ground. Wouldn't this create hell for them and me (trying to explain the difference)? Let me know what you think!

Christian Offenburger, RPLS
Houston, TX

That's my problem exactly.

I think all these people can "accept" a small error much better than they can accept SPC with a statement about ratios.

My county's GIS system is on SPC and it is stated as such, but if I mention SPC's to the people running the GIS, they give a stupid look and say not to use SPC's. So, I pretty much use SPC's(ratios of about 0.99995) and let the next surveyor question my 0.05' error per 1000 feet.

You are surveying to make information about a project correctly avaialble to the public. If you provide a full SPC survey to a client and that is all, how have you sreved him. A 149.99' wide by 290.38' deep lot may be an acre on the ground, but it is 43,554 s.f. in the planning boards mind and will never get approved. Survey in US feet on the ground and on your map.

As for SPC, provide metric coordinates for your P.O.B. and enough to satisfy requirements, 2 or 3 total is usually satisfactory. Using metric will dissuade the majority of the nonsurveying public. Provide all three scale factors for your P.O.B. and one for the project. Do not put your geodetic North on the North arrow, but instead in your SPC report.

unless you are buying sophisticated software, do you computer work in plane surveying and convert at the end. If you cannot sit down and satisfactorily teach SPC to another surveyor, you are probably just piling up male bovine excrement to use it on a survey plat.

Paul in PA

Phil:


Here is the link.

TAP HERE FOR A LINK TO http://www.ngs.noaa.gov/PUBS_LIB/develop_NSRS.html

One way to create a link is to look at a posted message like this one, press the right mouse button and press "view source". You can then copy the source to the notepad, change what you need and save the file using the name you like with ".html" at the end (ej: link-noa.html"). Remember to save the file as a TXT file.

Good thoughts, Paul.

Christian Offenburger, RPLS TX

The problem with accurate SPC dimensions is the same as virtually as accurate ground measurements.

So my 100 X 435.60 lot is actually 99.995' by 435.575, what about the bulk of surveyors, who when followed by another surveyor seems to have some sort of minor disagreement in measurement?

I'll tell you this, if I measure 100 X 435.60 SPC, no surveyor, in my area is going to follow in my footsteps and find some thing less.

The minor differences between ground and SPC needs to be addressed by the Planning Commissions. SPC will be the eventual wave of the future.

Did you know, at one time surveyors in W. Virginia used to use slope distances?

Anyway, as far as Planning Commissions are concerned, there should be a consideration made for SPC coordinates and derived courses.

It just needs to be addressed and I'm not inclined to work a bastardized survey system between two sets of coordinates all the time.

By the way, I work in a county that has a basemap based on SPC and aerials with 1/2' pixel resolution.

The neighboring counties are taking about having new aerials taken with 1/4' pixel resolution. If this keeps up, the difference in SPC and ground dimensioning will be apparent on individual jobs. As of now, if there are 2 or 3 adjacent jobs the apparent difference between SPC and ground is already apparent.

Plane(plain) and simple, SPC is the future.
Modified By John Francis on 2/21/2004 at 8:57 PM