Andy-sorry to have hijacked your thread. State Plane Coordinate Systems filled an important gap when they were first devised. They work well even today for point addressing although perhaps not the best option available. Over reporting in lat long the SPC are more easily visualized. I can mentally picture a meter or foot more easily than a second of latitude. But SPC inverses are poor representations of vectors on the ground. Clearly SPC have been around a long time and the parameters are more available than a county or city wide projection would be but only marginally so. How many consumer GPS receivers natively support SPC? How many digital quads and aerials are in SPC? I would submit that the best option today might be to work in a custom low distortion projection and publish coordinates on key positions in UTM. UTM has horrendous scale factors but if the working projection is low distortion it won't matter. UTM is globally recogmized and provides relatable values. I don't hate SPC systems I just think their time is coming to a close. It's a system that was only ever really adopted by surveyors and civil engineers and sadly wasn't really understood by most of them.
AMEN
I agree. While SPC's may have had their useful purpose, why not use, especially for those of us at higher altitudes, a low distortion projection vs a high distortion projection (SPC)?? LDP's are more representative of actual ground distances and are (if properly done) closer to true bearings. I can't recall any time in my career when I've used SPC's or any situation where they would have been a good alternative to LDP's.
LDP's are easy to use, and if one is working off of accurate lats/lons via OPUS for example, moving from one LPD to another or even SPC's is a snap.
SPC is a projection. LDP is a projection. Projection, Projection, Projection... as a realtor would say Location, Location, Location... it's all the same. With a basic understanding, I think surveyors can unchain themselves from this crap of utilizing outdated SPC projections.
Pablo B-)
> I think surveyors can unchain themselves from this crap of utilizing outdated SPC projections.
You guys at elevation have a legitimate gripe about SPC projections, but don't forget that a lot of us don't have that problem, and there's a lot to be said for standardization. When I put a note on a map or other document that says "horizontal dimensional values are referenced to CCS83 (2010) Zone II," I don't have to say anything else to allow anyone using the document to follow my work.
In my home town, the CCS83 Zone II combined scale factor runs right about 0.99996. Four hundredths in a thousand feet is close enough for almost all practical purposes. The local university campus uses plain old CCS83 Zone II for everything, even the biggest building projects. The site surveyors basically localize on the nearest control points and lay everything out in US feet with no scale corrections. No LDP necessary.
While LDPs have their place, don't diss SPC projections just because they don't work so well in your area. Some of us like it just fine.
Right On!!
You still have the north isn't north issue. At 2000 feet the new punch mark might not hit the DOT marker either.
B-)
> At 2000 feet the new punch mark might not hit the DOT marker either.
It wouldn't hit a Caltrans marker; it might still work i TX.
> SPC is a projection. LDP is a projection. Projection, Projection, Projection... as a realtor would say Location, Location, Location... it's all the same. With a basic understanding, I think surveyors can unchain themselves from this crap of utilizing outdated SPC projections.
>
>
> Pablo B-)
You can have my SPC projections when you pry them from my cold dead hand...
I'm in Florida, so I consider being at high elevations when I get over 250 feet. Most of the time we don't even worry about the elevation scale factors because we work so close to the ellipsoid anyway. The Florida East and West Zones along the peninsula were made narrower than usual, because one zone wouldn't meet the 1:5000 limit. So scale factor errors top out at around 1:7000 at most.
> > SPC is a projection. LDP is a projection. Projection, Projection, Projection... as a realtor would say Location, Location, Location... it's all the same. With a basic understanding, I think surveyors can unchain themselves from this crap of utilizing outdated SPC projections.
> >
> >
> > Pablo B-)
>
> You can have my SPC projections when you pry them from my cold dead hand...
>
> I'm in Florida, so I consider being at high elevations when I get over 250 feet. Most of the time we don't even worry about the elevation scale factors because we work so close to the ellipsoid anyway. The Florida East and West Zones along the peninsula were made narrower than usual, because one zone wouldn't meet the 1:5000 limit. So scale factor errors top out at around 1:7000 at most.
Oops, I meant the scale factor errors for the east and west zones in Florida don't exceed 1:17,000 instead of the 1:10,000 limit.
So long as the scale factors are accounted for, there is no error in SPC. It is perfect mathematically. But even at 1:17,000 you're looking at a 58.8 parts per million scale factor, which for most applications is too much to ignore. With an LDP at the county wide level, you could be looking at 5ppm at the extreme, which is often small enough to ignore (1 mile x 5 ppm = 0.026'). I don't have a problem with surveyors using SPC, provided they produce them properly. We still publish our boundary corner monuments with SPC (while using LDP as the underlying, working projection for field work and CAD work), but I'm thinking there is a better way. Just spit-balling, I think that way may be LDP with UTM, LDP with LLH, or LDP with published county wide projection data recording at the county court house.
Mapping projections are just another TOOL in the box. If SPC or UTM Projections serve your particular purpose, GREAT...USE THEM (in their pure form). If you have to 'modifrickingfy' them, then obviously 'they' are NOT suiting your purpose.
Like any TOOL, understanding the proper usage and application is critical. If you don't know how to use a tool, maybe you should either learn, or find someone to help you out, BEFORE you do any permanent damage. Mapping Projections are a little like chainsaws, they are great IF you know how to use them, but dangerous if you don't.
As far as perpetuating your spatial position on a plat or in a description... I [personally] think that geocentric X/Y/Z is the hot setup, IF you are using GPS/GNSS. If on the other hand, you are using a Total Station (or transit/chain), then SPC might be a better solution for some.
IT DEPENDS...
At the risk of starting WWIII, here's something to chew on:
If you are using GPS and the CORS, then you can actually perpetuate the geodetic position of a given point on the earth with as much (or more) accuracy by returning [publishing] an IGS2008 XYZ at the time of observation (say Epoch 2013.1234), as you can with a NAD83(2011) Epoch 2010.0000 position.
Loyal
I'm not really up on how everyone constructs their LDP's. I will use the default Transverse Mercator projection offered in Trimble's coordinate system. However, if that is applied it still will set the projection at sea level. To get to your elevation you still need to apply a scale factor to your system. This isn't any different than doing it to SPC coordinates.
