Loyal, post: 454957, member: 228 wrote: Skeeter,
Where did I say ANYTHING about "State Plane Coordinates?"
I must be missing something...
Loyal
I assumed SPC stood for State Plane Coordinates. What other system do you use a TM which I assume is Transverse Mercator. I haven't been able to figure out what LDP stands for.
Skeeter1996, post: 454960, member: 9224 wrote: I assumed SPC stood for State Plane Coordinates. What other system do you use a TM which I assume is Transverse Mercator. I haven't been able to figure out what LDP stands for.
Skeeter, LDP stands for Low Distortion Projection, usually used when you want a small local projection with low PPM's (parts per million). Yes TM means Transverse Mercator, in Trimble you can set up an LDP for your site, you have lat, longs, projected into a local plane with defined parameters. Dr. Herb is the guy or one of them that set up the Montana State Plane system of NAD83. A calibration will do a projection of some kind, you just have little control over the parameters, they are hidden in the DC and will be very random, generally with large PPM's.
Skeeter1996, post: 454960, member: 9224 wrote: I assumed SPC stood for State Plane Coordinates. What other system do you use a TM which I assume is Transverse Mercator. I haven't been able to figure out what LDP stands for.
Nearly ALL of the Low Distortion Projections (LDP) that I use, are NAD83(whatever) Transverse Mercator Projections (I will at times, use an UNrectified Oblique Transverse Mercator Projection).
Some State Plane "systems" are also Transverse Mercator Projections, as well as obviously UTM Systems. Other State Plane "systems" are Lambert Projections, except Alaska Zone 1, which is an Oblique Transverse Mercator (rectified).
Sorry for the confusion.
Loyal
Loyal, post: 454962, member: 228 wrote: Nearly ALL of the Low Distortion Projections (LDP) that I use, are NAD83(whatever) Transverse Mercator Projections (I will at times, use an UNrectified Oblique Transverse Mercator Projection).
Some State Plane "systems" are also Transverse Mercator Projections, as well as obviously UTM Systems. Other State Plane "systems" are Lambert Projections, except Alaska Zone 1, which is an Oblique Transverse Mercator (rectified).
Sorry for the confusion.
Loyal
Your talking way over my head. You're one of the few guys on this Board who seems to know what he's talking about and I respect your responses. I just didn't connect site calibrations to your LDP relevance due to my ignorance of the subject matter you were trying to explain.
roger_LS, post: 454936, member: 11550 wrote: I don't use GPS in this area due to heavy tree cover and relatively smaller projects. Instead use resections off record calcs to get on to the bearing base of a map/deed and find more points. The resection is just to get you oriented than you've got actual side shots to everything. There are places for Compass and tape to get you started.
I trust that the bite wasn't too painful. Your presentation was misleading though, obviously others felt the same way. 🙂
We're in different worlds. I quit searching for corners your way years ago. I have my old GPS system I would make you a heck of a deal, but it's not a GNSS system and they are so much more quicker to record a position you wouldn't be happy with it. If there's just a little hole in the trees I can record a position. Deciduous trees usually move about in the breeze and you can usually squeeze out a position with a little patience.
It also stands for Lou Diamond Phillips
Loyal, post: 454962, member: 228 wrote: Nearly ALL of the Low Distortion Projections (LDP) that I use, are NAD83(whatever) Transverse Mercator Projections (I will at times, use an UNrectified Oblique Transverse Mercator Projection).
Some State Plane "systems" are also Transverse Mercator Projections, as well as obviously UTM Systems. Other State Plane "systems" are Lambert Projections, except Alaska Zone 1, which is an Oblique Transverse Mercator (rectified).
Sorry for the confusion.
Loyal
How do you correlate an older survey using map projections? Older surveys don't have any correlation to any map projections. They don't even tell you how they determined the basis of bearing. I maybe dumb, but I don't see any connection at all to what you're discribing and a site calibration.
When an older survey was laid out on the ground as a grid the surveyor was projecting his survey onto a geodetic surface. He just didn't know it, or for some old hands, he may have known, but he wouldn't have cared. After all some of the old guys would actually survey geodetically, that's why some old maps will show northing and westings.
When you show up with GPS ,what you are trying to do is create a projection with the parameters set to "mesh" into the older survey, this is what your calibration is attempting to do. I don't do that anymore, but Trimble used to use what they called a plane projection, I'm not sure what that really was but I assume it was used when calibrations were attempted.
Today I would imagine they use a TM projection for the calibration, they have to do something to get XYZ from lat, long, heights. In essence the calibration sets-up a projection probably at the point you tell it to with an origin lat long at say the section corner being the first point of the calibration then uses the xyz you assigned to that point. You then go to say a 1/4 corner locate it and tell it to rotate the calibration to that point, it sets the origin long as the central meridian through the first point and adds a rotation to a projection along the central meridian. I'm guessing about this process but it's got to be that or something similar.
I don't know what setting up a scale factor of 1 does in this situation. I do know that a scale factor of 1 for a TM projection would be unlikely to work very well. Maybe Trimble takes this into consideration and adjusts the scale somehow.
You have this powerful tool, you can set-up a predefined TM LDP in Trimble, you can get lat, longs for the corners off Google, Bing, quad sheets, GIS or even the GCDB to get search points in your system. Go to the field with the plat and set up your base then find the corners. You will probably find a rotation; that can be applied or if you want to hold the 96 bearings without a rotation you can actually slide your origin long until the bearings and the projection match, basically you retrace the 96 projection.
This way you have a defined projection with all the parameters known, it might have the central meridian on site being very close to true north and you can show record vs measured bearings, or you can slide the meridian east-west until you match the original bearings. Either way you can simply state your metadata and allow anyone to almost perfectly retrace what you have done. They don't need your lat, longs, or your coordinates on the points, although that would be nice, they do need to know your origin lat, long, scale, that it's TM NAD83, the epoch is nice, telling what CORS you tied into is good. As an added bonus you have good elevations with a Geoid model, ties to CORS, or even better bench marks if available, the calibration has to do something with elevations, a two point one is dangerous for sure, not that you will care all that much doing a boundary, but we live in a 3d world and having good elevations on each corner has value and is very quick to do since you are already there. The LDP you set up with have small ppm's a defined projection, an easily retraceable system, good elevations, and something that when you are nearby you can jump right on and do another survey and extend it much father than you would want to do with any calibration.
That's a pretty good question, but the answer varies quite a bit depending on the ??original? survey that you may be retracing.
The PLSS Rectangular Surveys (Sections, Townships), setting up an LDP is pretty straight forward (depending on the topographic relief involved). North is Astronomic North (which for most practical purposes coincides with Geodetic North), and the Distances coincide with Ground Distances.
Later Surveys within a given Section, are [usually] based on either an Astronomical Observation, or aligned with one (or more) of the Original ??Lines,? and Distances are/were measured along the Ground.
The are some Original Surveys that were returned in State Plane Coordinates, but they are pretty rare around my neck of the woods.
The are quite a few DOT Surveys that were returned in Modified State Plane Coordinates, these can be a little tricky to set up, but certainly doable.
Most of the old Town Site Surveys (again in my neck of the woods), where surveyed by US Deputies, Mineral Surveyors, Railroad Surveyors, or Civil Engineers, and it usually isn't too difficult to figure out what they did, and how they did it.
In any case, the geometric concerns involved when taking what were in many cases a Flat Earth spatial paradigm, and applying a formal mapping projection to ??best fit? it, is not without its own basket of assumptions and trade offs.
If you are trying to MATCH just one Survey (surveyor), then it's a lot easier than piecing together a dozen or more Surveys spanning 100+ years, and several thousand feet of Elevation change.
Personally, I'd much rather retrace a 150 year old Mineral Survey done by a competent US Deputy Mineral Surveyor (most were), than try and figure out what is going on with a ??modern? residential subdivision that lacks any coherent spatial integrity (or reasonable metadata).
On thing that I like about rplstoday, is that just about every ??type? of Surveyor (and survey) is represented here. Some of us are very specialized, others are ??general practitioners.? What works in (dare I say it) Texas, doesn't necessarily work in the PLSS of the Rocky Mountains, or the plains of Kansas (not to mention downtown LA or New York City).
Well, I have lost track of what we were talking about, and need to get back to work so I can get to the Geezer Club Safety Meeting this afternoon.
We can continue this later,
Loyal
Skeeter1996, post: 454857, member: 9224 wrote: I forgot to hold the scale factor to 1.00 in my 2 point calibration. That is the problem. Now I'm trying to defend why I even do site calibrations. Thanks for the tip!
Hey now!! I think I said it was not fixing the scale factor to ONE first. just sayin!
There's nothing wrong with using site calibrations as long as you are careful and understand what's going on.
1 Point "here" position gives no residuals at all, and assumes no error in seed point
2 point calibration (with floating scale factor) will also give NO residuals, because it will show the record/measured distance between those two points as errorless. But, it will use whatever scale factor it calculates to make that error disappear on every other measurement. Just try it out. key in two point pairs, then take two shots. makes no difference what the distances are, (edit... yes there are generally limits to what the software will allow. I meant only in the usual realm of survey differences) the results will be a perfect fit.
2 point calibration ( scale factor fixed at 1) here is where you can start to get useful information.... it will give you residuals.
3 point calibration is where "least squares" starts in. now it will give you mathematical estimate of the difference between the record and measured in distance and rotation. good way to toss out bad points... add shots to the calibration and see how it affects the system in real time.
of course you can add vertical or not to any of these calibrations. that's a whole nother discussion!
Andy J, post: 455079, member: 44 wrote: Hey now!! I think I said it was not fixing the scale factor to ONE first. just sayin!
There's nothing wrong with using site calibrations as long as you are careful and understand what's going on.
1 Point "here" position gives no residuals at all, and assumes no error in seed point2 point calibration (with floating scale factor) will also give NO residuals, because it will show the record/measured distance between those two points as errorless. But, it will use whatever scale factor it calculates to make that error disappear on every other measurement. Just try it out. key in two point pairs, then take two shots. makes no difference what the distances are, (edit... yes there are generally limits to what the software will allow. I meant only in the usual realm of survey differences) the results will be a perfect fit.
2 point calibration ( scale factor fixed at 1) here is where you can start to get useful information.... it will give you residuals.
3 point calibration is where "least squares" starts in. now it will give you mathematical estimate of the difference between the record and measured in distance and rotation. good way to toss out bad points... add shots to the calibration and see how it affects the system in real time.
of course you can add vertical or not to any of these calibrations. that's a whole nother discussion!
Okay Andy maybe it was you that steered me to the scale factor, Sorry. The wolves we're attacking me so ferousiously for even using Site Calibrations I may have gotten confused as to who told me what. Loyal is giving me a lesson in LDPs. I think I'm basically doing the same thing he is, but I'm still confused as to how he gets the calculated points to fit with what's on the ground.
There seems to be a lot of antiTrimble Site Calibration sentiment. I use it the same way you described. I just forgot about holding the scale factor this one job. Once you go past a three point Site Calibration things can sometimes go nuts. I always feel uneasy if the residuals go above a tenth.
Skeeter1996, post: 455085, member: 9224 wrote: Okay Andy maybe it was you that steered me to the scale factor, Sorry. The wolves we're attacking me so ferousiously for even using Site Calibrations I may have gotten confused as to who told me what. Loyal is giving me a lesson in LDPs. I think I'm basically doing the same thing he is, but I'm still confused as to how he gets the calculated points to fit with what's on the ground.
There seems to be a lot of antiTrimble Site Calibration sentiment. I use it the same way you described. I just forgot about holding the scale factor this one job. Once you go past a three point Site Calibration things can sometimes go nuts. I always feel uneasy if the residuals go above a tenth.
Okay, I'm starting to understand your "dilemma" a little better.
I have a butt load of work still in front of me tonight, but I'll try and get back to this tomorrow.
I can tell you right now, that we are talking apples and oranges, and you may very well NOT agree with my philosophy concerning "retracement."
Loyal
Loyal, post: 455103, member: 228 wrote: Okay, I'm starting to understand your "dilemma" a little better.
I have a butt load of work still in front of me tonight, but I'll try and get back to this tomorrow.
I can tell you right now, that we are talking apples and oranges, and you may very well NOT agree with my philosophy concerning "retracement."
Loyal
Loyal,
I'm simply trying to find pins set by another Surveyor by calibrating my calculated position to GPS positions in my GPS to their actual positions on the ground. Trimble site calibrations has worked for me numerous times on prior projects. On the one I'm having trouble with trying to calibrate using a not so good Surveyor's data, things went South on me.
You indicated that you used a system that did not rely on site calibrations, but somehow using LDPs you eliminated site calibrations. That process intrigues me. With my current knowledge I can't understand how that is possible.what process are you using to compute a accurate position for previously set corners without tieing into a corner on the ground and making some kind of an adjustment to create a more accurate LDP. It's just not possible in my mind, but I'm a mere human.
Hope that clarify my dilemma.
Skeeter1996, post: 454887, member: 9224 wrote: Well he ask "Why would you ever do a localizations or a Site Calibration". I assumed he didn't know why one would do one, so I politely told him why.
Know I don't know why a Surveyor would be Least Squares Adjusting his survey in this day and age. All it does is smear your errors all around mathematically. How would it ever help make a GPS survey more accurate?
why a Surveyor would be Least Squares Adjusting his survey in this day and age. All it does is smear your errors all around
Apparently there's a lot about LS adjustment adjustments you don't understand. A properly configured, accurately weighted LS adjustment isolates blunders and evaluates error. My question is why would a surveyor in this day and age not use state of the art data reduction, error analysis, and buinder detection?
In a proper network I find the one (or two) measurements that is genuinely problematic because that error wasn't smeared around.
Smearing around errors/mistakes is compass rule.
Why a surveyor would use LS adjustment? Because that's what professionals do.
Larry Scott, post: 455177, member: 8766 wrote: why a Surveyor would be Least Squares Adjusting his survey in this day and age. All it does is smear your errors all around
Apparently there's a lot about LS adjustment adjustments you don't understand. A properly configured, accurately weighted LS adjustment isolates blunders and evaluates error. My question is why would a surveyor in this day and age not use state of the art data reduction, error analysis, and buinder detection?
In a proper network I find the one (or two) measurements that is genuinely problematic because that error wasn't smeared around.
Smearing around errors/mistakes is compass rule.
Why a surveyor would use LS adjustment? Because that's what professionals do.
And then you use the LS numbers or stay with your original numbers? Are you just using it to evaluate your survey for errors and blunders or are you using the LS numbers to publish a perfect survey. I'm not trying to be insulting just trying to clarify what your using it for.
So you're saying if you don't LS adjust your survey you're not professional? I used it back in the day of transits and chains and it caused more problems than it ever found. It appears to me it's just an elitist's tool that feeds their egos. Now I'm being insulting.
Skeeter1996, post: 455197, member: 9224 wrote: And then you use the LS numbers or stay with your original numbers? Are you just using it to evaluate your survey for errors and blunders or are you using the LS numbers to publish a perfect survey. I'm not trying to be insulting just trying to clarify what your using it for.
So you're saying if you don't LS adjust your survey you're not professional? I used it back in the day of transits and chains and it caused more problems than it ever found. It appears to me it's just an elitist's tool that feeds their egos. Now I'm being insulting.
For LS to be meaningful, its application is suited to properly configured and weighted networks. A traverse, absent redundancy, LS isn't beneficial.
How about a recent example... Establishing control on 22 ac site. Initial survey was a perimeter traverse, 4 inter visible corners, with a satisfactory closure. 0.05 ft. As the project progressed 6 additional control points were established and a complex network resulted. However, the network returned a significant distance error factor. One of the distances, from the initial boundary, returned a residual far greater than any other. So to your question: use the LS adjusted value? The initial traverse looked good. That one (1000 ft) distance was remeasured and was found to be 0.10' shorter. (Slope distance mistaken for horizontal distance.) The LS adjustment isolated the error, not smearing the error around. The adjusted value was in fact correct.
Is that elitist? I'll let you decide.
Larry Scott, post: 455203, member: 8766 wrote: For LS to be meaningful, its application is suited to properly configured and weighted networks. A traverse, absent redundancy, LS isn't beneficial.
How about a recent example... Establishing control on 22 ac site. Initial survey was a perimeter traverse, 4 inter visible corners, with a satisfactory closure. 0.05 ft. As the project progressed 6 additional control points were established and a complex network resulted. However, the network returned a significant distance error factor. One of the distances, from the initial boundary, returned a residual far greater than any other. So to your question: use the LS adjusted value? The initial traverse looked good. That one (1000 ft) distance was remeasured and was found to be 0.10' shorter. (Slope distance mistaken for horizontal distance.) The LS adjustment isolated the error, not smearing the error around. The adjusted value was in fact correct.
Is that elitist? I'll let you decide.
I think worrying about a .10 error is elitist. So in short you just use the LS numbers to check for your errors and send a crew out to fix a .10 blunder? Or do you just use your LS number and call it perfect? Just asking not mocking.
Skeeter1996, post: 455206, member: 9224 wrote: I think worrying about a .10 error is elitist. So in short you just use the LS numbers to check for your errors and send a crew out to fix a .10 blunder? Or do you just use your LS number and call it perfect? Just asking not mocking.
I'm trying to find out why my GPS adjusted my whole survey and introduced a 10 foot scalar into the entire job. I don't think LS or LDP's amount to a hill of beans in my problem. I quit using LS when the Cost outweighted the benefit. The only benefit is to the programmer who writing useless software that elitist's keep sending money to so he can fix his programs bugs with updates. Hopefully you don't do alot of worrying about tenths of a foot do you? Now I'll have the programmers nipping at my heels. Just curious how do you misrecord a slope distance for a horizontal distance these days? I'm in the dark about what kind of equipment you're using so it's hard for me to comprehend your love of LS. I've never seen someone LS adjust a RTK survey so I don't have a clue how they are doing it. There can only be a few professionals out there doing it.
Skeeter1996, post: 455206, member: 9224 wrote: I think worrying about a .10 error is elitist. So in short you just use the LS numbers to check for your errors and send a crew out to fix a .10 blunder? Or do you just use your LS number and call it perfect? Just asking not mocking.
Sorry I reread your post and you do send a crew out to fix it. Now that's Elitist!
Skeeter1996, post: 455210, member: 9224 wrote: Sorry I reread your post and you do send a crew out to fix it. Now that's Elitist!
It was an ongoing project, so it was checked. If not, the adjusted value would stand.
Hopefully you don't do alot of worrying about tenths of a foot do you? Hopefully I do. High precision work returns higher fee. And steel fabrication has to fit. That's not elitist. Stake a rail yard switch, or bridge span, off a tenth and see what happens. With a properly configured network, AND with LS adjustment there's no worrying about 0.10'. That's the point!
