> We've been dicussing the problem of the 3D survey for quite a while. I'm working on a project right now that the client wants on the local SPCS. This area has a combined scale factor of 1.0007.
Mr. Moe,
Where are you working that gives you such a huge scale-factor? It must be on mountain-top to mountain-top surveys on some 14,000' peaks? Just curious. I agree with your point (or a point if it's not yours exactly) that measuremenents between corners should be shown as what they would measure if you pulled out a tape and measured them level. When a landowner wants to know where he owns to, he (more often than not) wants to know how many feet it is from property corner to property corner.
On the more general discussion going on, I am a little concerned with showing elevations that can be misconstrued for most clients. However, if you provide them with geodetic coordinates so they can navigate to their corner locations, the elevation factor may indeed help them get to the right point. ellipsoid factors can definitely be confusing for many laypersons.
Combined Scale Factors
.9997 really isn't all that huge (relatively speaking).
On Point "Evanston" (NGS PID MR0820) the Combined Factor is .99967373 (Wyoming West), .99962339 (Utah North), and .99926670 (UTM-Zone 12), and that's a good 100 (vertical) feet below my house!
Montana Scale Factors (NAD83) are about .999392 along the central parallel, and that's at the Ellipsoid. Add another 100 ppm for each 2100 feet of Ellipsoid height.
I've seem UTM combined factors up (or is it "down") around .9991 in central Utah, and ~1.001 in Southern Iraq. There are probably places in Montana (SPC-83) that are worse than that!
Loyal
I liked Kent's 1st reply.
Here is an intresting one:
> If we are going to hang our hat on retrodicted coordinate estimates (which I think is FINE [within reason]), then what is really the point of ADDING the additional transformation to NAD83xxxx? If the velocity field model is accurate, then it doesn't matter one iota WHEN you observe a given point, it would still transform BACK (or forward) to the same ITRFxxxx/NAD83xxxx Epoch whatever coordinate that was originally published.
>
> I say...”publish” where your points are TODAY (ITRF2000, ITRF2005 or ITRF2008, Epoch 2011.xxxx) in geocentric Cartesian Coordinates (X,Y,Z in meters), and let the next guy use the LATEST velocity field model (HTDP/TDP v.X.x) to estimate where that point might be on THE DAY that he is THERE (in whatever ITRF realization is current/convenient for him).
That pretty much ignores the entire cadastral reason for using standard projections and standard reference frames, though, which is to be able to easily evaluate the relative positions of various other properties surveyed by other surveyors at different times. This is obviously more of a problem in Texas where the original land grants are controlled by much more widely spaced monuments than in the Eastern metes and bounds states and PLSSia, but in all cases I'd think that the ideal is to be able to easily assemble the "picture" of what evidence prior surveyors have found, and where it is. Having to massage each surveyor's work to put it all into some common reference frame is less efficient than simply adopting on in the first place.
When NAD83(COR96)Epoch 2002.0 needs to be abandoned, adopting a new standard will still be simpler than encouraging the proliferation of as many different projections and reference systems as there are properties to be surveyed.
Combined Scale Factors
> .9997 really isn't all that huge (relatively speaking).
>
> On Point "Evanston" (NGS PID MR0820) the Combined Factor is .99967373 (Wyoming West), .99962339 (Utah North), and .99926670 (UTM-Zone 12), and that's a good 100 (vertical) feet below my house!
>
> Montana Scale Factors (NAD83) are about .999392 along the central parallel, and that's at the Ellipsoid. Add another 100 ppm for each 2100 feet of Ellipsoid height.
>
> I've seem UTM combined factors up (or is it "down") around .9991 in central Utah, and ~1.001 in Southern Iraq. There are probably places in Montana (SPC-83) that are worse than that!
>
> Loyal
Loyal, .9997 is .0003 away from 1, or 3/10,000. 1.0007 is more than twice that. Most grid scale factors are extremely close to 1 here, and it is generally the elevation scale factor that controls ther greater "combined" scale factor value. I am only familiar with what I use in Colorado, and don't know much about UTM values being as large .9991; but that is relatively large to me. It sounds like those UTM zones and some other state's SPC map-projection configurations have larger grid-scale factors. (?)
Well first...NAD83(CORS96) Epoch 2002.0000 will be history by Spring. It's being replaced by NAD83(CORS96a) Epoch 2010.0000.
Besides which, my point above obviously went right over your head. IF you (well maybe not you), have the ITRFxxxx Epoch XXXX.xxxx Coordinates of a point (any point) you (well maybe not you), can easily transform that to NAD83(CORS96) Epoch 2002.0000 with the push of a button (if that's the spatial paradigm you wish to use).
The advantage to maintaining the “database” in ITRFxxxx Epoch XXXX.xxxx XYZ (day of observation), is simply that the best available velocity model can be used to generate coordinate estimates at a common epoch (whatever Datum/Realization and/or Epoch blows yer skirt up) that is independent of older (and less accurate) velocity models.
Loyal
Let me clarify
I do collect lat/long values on some of the claim corners which allows projection of the lines and overlaying of the claim pattern with digital quads. In fact, at the beginning of the project, some of the claims had been staked 10 years ago and allowed to lapse so once I found one of the old stakes, I was able to find the rest with a hand-held GPS just by projecting the bearings and distances and remarking the old stakes with the new info.
What I meant by "nobody cares" is that precise geodetic co-ordinates of the claim corners is not something that I can see a particular use for in this project. So far we've set about 1000 2" X2" X4' stakes 295' to 600' apart. Any missing stake can be replaced quite readily by reference to others nearby. Any geological features, roads, other found claim corners, etc. can be plotted with sufficient accuracy by collecting a hand-held lat/long or by direct ground measurement and plotting in relation to our claim pattern and topos.
Let me clarify
> Any geological features, roads, other found claim corners, etc. can be plotted with sufficient accuracy by collecting a hand-held lat/long or by direct ground measurement and plotting in relation to our claim pattern and topos.
Is the answer mainly that you aren't actually using survey-grade GPS in this work?
OOPS
My mistake, I read 1.0007 and it got translated into my pointy head as .9997 (me bad).
You are absolutely right about UTMs and Montana (SPC83) using much larger scale distortions (Zones are much bigger) than State Plane Systems.
Loyal
Kent
Yes, that is the reason. As I've mentioned before, my nice Topcon (Javad) RTK system is now junk after the receivers "fried" for some reason that the Topcon people can't explain. If it was still working, I'd be using it out there and probably getting it done more efficiently. After checking rental rates for a GPS system, my decision was that I'd rather pay my field guys and get the job done a little slower than line the pockets of the equipment dealer and get it done faster.
A couple of times a year, I get a job that doesn't make sense to do conventionally and I get somebody with GPS that works to help me out on it.
Combined Scale Factors
It's in Montana. Believe me I was quite shocked when I started to do the control for the job and looked at the parameters (state plane is something I try to avoid in Montana-having your plat tilted 2-4degrees just bothers me). The elevation is actually less than 2500' so I assumed a small scale factor. Not so!
I'm used to high elevation projects and will see 1.0004 as a large number, but the lambert projection and one zone that is used in Montana is going to produce some large scale factors and my 1.0007 is probably not close to the largest.
However, we are getting off Geeoddmike's point. So for me I would say a class on real world 3D surveying. One that would take the 3D info that I base all my surveys on and get it into a map format that could be useful in a legal sense. It's where I think we're going. Doing each project as a Low Distortion Projection is where I am now; but it is a poor substitute.
> IF you (well maybe not you), have the ITRFxxxx Epoch XXXX.xxxx Coordinates of a point (any point) you (well maybe not you), can easily transform that to NAD83(CORS96) Epoch 2002.0000 with the push of a button (if that's the spatial paradigm you wish to use).
>
> The advantage to maintaining the “database” in ITRFxxxx Epoch XXXX.xxxx XYZ (day of observation), is simply that the best available velocity model can be used to generate coordinate estimates at a common epoch (whatever Datum/Realization and/or Epoch blows yer skirt up) that is independent of older (and less accurate) velocity models.
You've just described a worst-case scenario. The only way that you could top it would be to have each project on its own custom projection. :>
I guess it is just too simple to bump NAD83 reference systems in discrete jumps between standard epochs such as from 2002.0 to 2010. Over a county-size area for most of the US, that ought to be almost a simple translation in horizontal components.
Not sure how we were able to lay out that 5' x 140' parcel a couple of days ago without $100,000 worth of GPS equipment and 5 years of fulltime study of geodesy.
Holy hell Kent when you are in a hole for goodness sakes quit digging LOL.
> Holy hell Kent when you are in a hole for goodness sakes quit digging
You can't be serious. Loyal's desire to see wholesale use ITRF coordinates would be an incredible train wreck. Add custom projections for each of ten adjacent tracts and you've got a Zeppelin crash thrown in for good measure.
Holy
I'm glad somebody understands all that stuff like Loyal and others. I have come to the conclusion that I'm not going to ever be that guy. My hope is that when and if I get back into the GPS business that the equipment and process of measuring stuff with it is something I can understand and utilize without hurting my head. I hope that about a lot of stuff, though, and still my head hurts a lot of the time.
I apologize for even getting involved in this thread, come to think of it.
Holy
> I'm glad somebody understands all that stuff like Loyal and others. I have come to the conclusion that I'm not going to ever be that guy.
Well, you have just made my point perfectly, Steven. The object is that surveyors actually use geodetic reference systems in cadastral work. That necessarily means keeping things simple and efficient.
Kent
Could you state your point again that I made perfectly? Thanks.
I hate to be the one to break the news to ya Kent, but NAD83 (all flavors) is headed to the scrap heap in the next few years (2018 or thereabouts).
If you want to “bump” your old NAD83 Coordinates around based on what will soon be an obsolete datum, nobody is going to try and stop you.
Maybe you didn't get the memo, but the National CORS has been intrinsically based on “odd epoch” ITRF2000 Coordinate estimates for quite some time. YES....those “odd epochs” are transformed (extrapolated) to Epoch 2000.0000 (using various versions of HTDP), before the coordinate estimates are published in the NGSIDB, but they are still BASED on the “odd epoch” estimates and whatever version of HTDP that was current at the time they were published.
This (I believe) will change for the vast majority of the NGS CORS with the introduction of the Multiyear Solution later this year (in ITRF/NGS 2008), but that's a whole nuther story.
Modern geospatial positioning is continuing to evolve, and most of us will be around long enough to see the New Geocentric NSRS replace the old NAD83xxxx based NSRS.
If it makes you happy, I'm sure you can stay in your neolithic 2+1 spatial paradigm as long as you like...shucks, some folks are still living in NAD27.
Loyal
Kent
> Could you state your point again that I made perfectly?
The point is that in order to make a contribution, a geodetic reference system needs to be actually used by land surveyors who have a wide spectrum of other things to deal with in the course of surveying work. The system needs to be one that a surveyor of ordinary intelligence and experience can use with a minimum of effort but which performs the essential function for which a geodetic reference system is intended.
My new criterion may be if Cousin Steve can't use it, then it isn't going to be widely adopted.