When publishing a plat, that's on spc, with lots. Of relief, or elevation difference, do you put the elevations on it too, so that the scale differences can be applied?
I used to tie into Bobby Matchet's work, (USFS), and NOT understand why my distances were always longer than his.... Well, he was working spc. Around here, grid to ground is around 100 ppm, or 1.000100 csf. This equates to around 1/2 foot per mile.
BTW, where is Bobby?
He used to wrangle and fuss with the USFS. About survey proceedure. Finally, he caved, and told his crews "put ZSC" on it. That meant Zone Survey Crew. This really created some messes. It was (imho) Bobby's revenge, for the local usfs rangers telling him to hurry up... (It was nothing more than the old war... Faster, cheaper etc.)
As we move away from Total stations, and more towards gps, It is easier to stay "on the grid". I was one of those guys, that did not know about scaling the total station distances... I do now.
Nate
Nate The Surveyor, post: 450270, member: 291 wrote: When publishing a plat, that's on spc, with lots. Of relief, or elevation difference, do you put the elevations on it too, so that the scale differences can be applied?
I used to tie into Bobby Matchet's work, (USFS), and NOT understand why my distances were always longer than his.... Well, he was working spc. Around here, grid to ground is around 100 ppm, or 1.000100 csf. This equates to around 1/2 foot per mile.
BTW, where is Bobby?
He used to wrangle and fuss with the USFS. About survey proceedure. Finally, he caved, and told his crews "put ZSC" on it. That meant Zone Survey Crew. This really created some messes. It was (imho) Bobby's revenge, for the local usfs rangers telling him to hurry up... (It was nothing more than the old war... Faster, cheaper etc.)
As we move away from Total stations, and more towards gps, It is easier to stay "on the grid". I was one of those guys, that did not know about scaling the total station distances... I do now.
Nate
Short answer is no, no elevations are published.
The last one I did had 200' in elevation change so about 5ppm across the site.
In the past I expressed my opinion that it would be great to have elevations shown on boundary monuments (where available) to determine how deep to dig, whether the area has been filled or cut, and to help determine if it has been disturbed. Of course that elicited various negative reactions here, ranging from someone will use it as a benchmark to "what a stupid idea". Just saying, if you could put a good elevation on a monument, why not do it. It is up to the next surveyor to know whether or not or even how he should use it
John Hamilton, post: 450273, member: 640 wrote: In the past I expressed my opinion that it would be great to have elevations shown on boundary monuments (where available) to determine how deep to dig, whether the area has been filled or cut, and to help determine if it has been disturbed. Of course that elicited various negative reactions here, ranging from someone will use it as a benchmark to "what a stupid idea". Just saying, if you could put a good elevation on a monument, why not do it. It is up to the next surveyor to know whether or not or even how he should use it
My personal database is filled with good elevations on monuments for exactly the reasons you mention. I haven't quite come around to giving that to the public record yet.
Whether using SPC or some local datum, distances should be related to some common elevation. The guys in the mountains will tell you that total station closures (no geodetic positions involved) will suffer if the horizontal distances are not scaled to some common elevation due to Earth curvature. As a flat-lander, that's never been an issue. The rule of thumb is that every 21 feet of vertical difference will change the scale factor by 1ppm. So you have some wiggle room. Remember though that the scale factor is related to the ellipsoid height, not orthometric height.
So you could provide an ellipsoid height for all of your monuments to a precision of +/-10 feet and this would be good enough for determining a scale factor.
Ultimately, I think it's fine to provide a combined factor that is appropriate to the site and not be concerned with the ellipsoid heights. Having said that, as John points out, there is value in keeping elevations on boundary monuments.
I don't use SPC. I provide latitude and longitude on all of my plats and descriptions. My directions and distances are based on a local projection. In my metadata I state that bearings are related to a local grid with an origin of Lat x and Long y. I also state that my distances are expressed in US Survey Feet as measured horizontally along the surface of the Earth. I'm thinking that starting in 2018, I'll add the ellipsoid height of the projection as well so that anyone can re-create it.
John Hamilton, post: 450273, member: 640 wrote: In the past I expressed my opinion that it would be great to have elevations shown on boundary monuments (where available) to determine how deep to dig, whether the area has been filled or cut, and to help determine if it has been disturbed. Of course that elicited various negative reactions here, ranging from someone will use it as a benchmark to "what a stupid idea". Just saying, if you could put a good elevation on a monument, why not do it. It is up to the next surveyor to know whether or not or even how he should use it
I agree. I found a boundary monument, which was set flush at a toe of slope in the 80s, down 3.5 feet the other day. A reference elevation would have kept the spirits up while digging through the dirt, rock, and scrap metal. I actually thought about using "reference-only" elevations on my record of survey to assist the next Surveyor. I've seen records (City and private) with monument elevations & noted "elevations provided to assist with retracement only". Some LA City field notes have used an assumed 100.00 elevation- helps the next guy's search, but also guarantees it won't be used as a sea-level BM.
Here is a copy of corner record that is on file in L.A. County which has "convenience" elevations and a corresponding disclaimer.
If you don't have a great deal of relief across your project and the project doesn't span several miles, you could report a combined scale factor (CSF) used for the entire project based on an approximate horizontal center coordinate and an average elevation. If your project is 10000' across at the longest/widest point and has about 100' total elevation difference, then a project wide CSF based on average elevation and approximate center point will be within 2 or 3 PPM at any point within the project. That's plenty good enough for most work.
If you have several hundred feet or more of elevation difference, or if you are tying into control from a great distance away, you may want to report the scale factors and elevations for the distant control and may find it necessary to split your project into 2 or more areas based on one or more particular elevation contours and have a CSF for each.
I carry elevations through my control and for most found and set points, but I don't generally report specific elevations for any of those points unless I have a specific reason for reporting an elevation at a particular point.