rfc, post: 439390, member: 8882 wrote: I'm confused. Weren't the stars around, and their azimuth's measurable to within a few seconds or so, many years before State Plane Grids, GPS, the PLSS, or the Texas' unique equivalent thereof, existed? What's the problem here?:confused:
Well SOP back in the day (except in Texas apparently), was to use astronomical observations (Sun or Polaris).
Loyal
MightyMoe, post: 439391, member: 700 wrote: You would assume wrongly
Transverse Mercator Smercator. It's still a projection with unknown parameters. However, there isn't any question in my mind but that I could more efficiently solve those parameters knowing that the basic projection is TM rather than Lambert. Thanks.
rfc, post: 439390, member: 8882 wrote: I'm confused. Weren't the stars around, and their azimuth's measurable to within a few seconds or so, many years before State Plane Grids, GPS, the PLSS, or the Texas' unique equivalent thereof, existed? What's the problem here?
The basic problem was a practical one. If a significant object of the survey was to be able to plot the boundaries of the land covered by it on the county map and thus indicate that the land had been appropriated and was no longer eligible for location from the public domain, then the task was as much to report bearings that could be plotted on the county map as to report the true bearings of the same lines as nearly as a compass could measure them.
The systematic errors in the variations used in making those original surveys were mostly the product of antecedent conditions that pre-dated the Republic of Texas. The whole problem is what you get when the map is as important as the survey.
Kent McMillan, post: 439395, member: 3 wrote: Transverse Mercator Smercator. It's still a projection with unknown parameters. However, there isn't any question in my mind but that I could more efficiently solve those parameters knowing that the basic projection is TM rather than Lambert. Thanks.
Locate a few points and do a few simple calcs and the meridian will show itself, then a projection can be setup with all the metadata desired. Thanks
MightyMoe, post: 439399, member: 700 wrote: Locate a few points and do a few simple calcs and the meridian will show itself, then a projection can be setup with all the metadata desired. Thanks
Yes, it saves some significant amount of work to know that the Trimble RTK FUGARWE projection is a Transverse Mercator projection. Thanks for sharing your experience in that department.
Loyal, post: 439388, member: 228 wrote: All of the FUGARWE Trimble "calibrations" that I have seen lately, are expressed as Transverse Mercator Projections. If you can get a copy of the "original" Data Collector (.dc) file, you can generally extract the projection parameters. That doesn't justify the use of such behind the curtain BS (IMO), especially when the USER has no clue what is going on behind said curtain.
Loyal
It is safe to assume that these are always TM if produced in the last 10 years by a yellow box by a button pusher. The ones that are not TM will include beautiful metadata on drawings because the operator really knew what they are doing. I end up converting old jobs for customers every week, sometimes as many as 10 jobs per week. As Loyal says, if you can get the .DC file you are golden.
And while I am complaining about this, I am kind of shocked how many of these jobs don't have a GEOID in play. So the base gets initialized with an orthometric height in the box that says 'Ellipsoid Height'.
If the job originates in SurvCE they are typically the underlying state plane zone, modified with a combined scale factor that makes them 'Modified State Plane'. Typically the SurvCE jobs match SPC at the scale point which is typically the base point. In the SurvCE jobs there is also an ambiguity if the bases of bearings is SPC Grid or Geodetic. You need more than one file from the data collector to fully decode. However the new 'HTML' description button on the 'Equip: Localization: Points (tab)' button generates a nice, complete report.
I wrote a FAQ on the conversion [ Converting a TBC Project with Local Projection to a SurvCE Job ] in 2013 that I still use.
Of course, this won't help you because you are not going to have access to the job files typically.
Loyal: On the yellow side, I would expect the LDP to be setup with the CM and LofO to be the first point in the file, typically the base position. But in most of the jobs I convert, the LDP is setup on what appears to be a random point 'near' the first point in the job. It is not a rounded location (like the nearest whole 5 second Lat/Lon). Do you know how the point gets chosen?
Mark Silver, post: 439402, member: 1087 wrote: It is safe to assume that these are always TM if produced in the last 10 years by a yellow box by a button pusher.
That's particularly useful since most of the KTR (backwards RTK) equipment used in Texas during that period was probably Trimble.
Mark Silver, post: 439402, member: 1087 wrote:
Loyal: On the yellow side, I would expect the LDP to be setup with the CM and LofO to be the first point in the file, typically the base position. But in most of the jobs I convert, the LDP is setup on what appears to be a random point 'near' the first point in the job. It is not a rounded location (like the nearest whole 5 second Lat/Lon). Do you know how the point gets chosen?
I don't know Mark. I'm sure that there is some logic to it, but other than the obvious NEED to select a (specific) Meridian for rotational purposes (Grid North = "local" North), the selection of the Origin Parallel doesn't usually make much sense to me.
Loyal
Loyal, post: 439404, member: 228 wrote: I don't know Mark. I'm sure that there is some logic to it, but other than the obvious NEED to select a (specific) Meridian for rotational purposes (Grid North = "local" North), the selection of the Origin Parallel doesn't usually make much sense to me.
Is it, by chance, the meridian midway between the base and the rover position where the projection is first selected?
Kent McMillan, post: 439405, member: 3 wrote: Is it, by chance, the meridian midway between the base and the rover position where the projection is first selected?
The Meridian used (selected) is a function of the "local grid North" that one is trying to HOLD. The Parallel selected is usually near the center of the various POINTS "calibrated" to. I'm sure that there is more than one way to SETUP a Trimble Calibration, but most folks seem to used Easy Button.
Now in the case of an Oblique Transverse Mercator (which may find it's way into a calibration), then the Central Meridian (Geodetic North) selected would be related to the Local Grid North by a specific ANGLE, and the meridian selected would not be so important.
Loyal
Kent,
I think we are talking about different things here. After re-reading some of you posts above, you may be asking a different question than I was trying to answer.
If (as I suspect), you are asking about a simple "one point" calibration using a fugarwe position at the Base, then I suspect (maybe even assume) that Both the Meridian and the Parallel would be the fugarwe position at the Base. I'm sure that there are plenty of these kind of short cuts going on, but it's not something that I run into.
Loyal
Kent McMillan, post: 439387, member: 3 wrote: I don't know enough about the projections that the Trimble salespeople convinced their customers to use, but I assume that they are typically Lambert projections tangent to the ellipsoid at one particular latitude that happens to be where either the base was set up or the first rover shot was taken.
Mike Potterfield wrote a routine many years ago for the yellow machines that employs an Oblique Mercator projection. A simple rotation and scale to get to ground and presto, your yellow box is oriented to an old plat with an assumed basis of bearing. A friend swore by it, esp. for initial recon work.
Loyal, post: 439406, member: 228 wrote: The Meridian used (selected) is a function of the "local grid North" that one is trying to HOLD. The Parallel selected is usually near the center of the various POINTS "calibrated" to. I'm sure that there is more than one way to SETUP a Trimble Calibration, but most folks seem to used Easy Button.
Now in the case of an Oblique Transverse Mercator (which may find it's way into a calibration), then the Central Meridian (Geodetic North) selected would be related to the Local Grid North by a specific ANGLE, and the meridian selected would not be so important.
Loyal
So, what you're saying is that when you did this using Trimble equipment, the DC queried you for the longitudinal extents of your project? Somehow that just doesn't sound right. Are you really, really certain that was how it went down?
Gene Kooper, post: 439410, member: 9850 wrote: Mike Potterfield wrote a routine many years ago for the yellow machines that employs an Oblique Mercator projection. A simple rotation and scale to get to ground and presto, your yellow box is oriented to an old plat with an assumed basis of bearing. A friend swore by it, esp. for initial recon work.
Yes, and there is every reason to believe that if the dog hadn't stopped to defecate, he'd have caught the rabbit. But is either highly relevant to the question at hand?
Kent McMillan, post: 439411, member: 3 wrote: So, what you're saying is that when you did this using Trimble equipment, the DC queried you for the longitudinanal extents of your project? Somehow that just doesn't sound right. Are you really, really certain that was how it went down?
Not me Kent, I have never owned Trimble Equipment!
I do however help folks sort out these Trimble calibration misadventures from time to time.
Loyal
Loyal, post: 439413, member: 228 wrote: Not me Kent, I have never owned Trimble Equipment!
I do however help folks sort out these Trimble calibration misadventures from time to time.
So, basically you're posting as an innocent bystander who witnessed the whole thing? I understand and I hope your licensing board does as well. Or do they even care at all about stuff like this that seems important in Texas?
Kent McMillan, post: 439414, member: 3 wrote: So, basically you're posting as an innocent bystander who witnessed the whole thing? I understand and I hope your licensing board does as well. Or do they even care at all about stuff like this that seems important in Texas?
Goodnight!
Kent McMillan, post: 439412, member: 3 wrote: Yes, and there is every reason to believe that if the dog hadn't stopped to defecate, he'd have caught the rabbit. But is either highly relevant to the question at hand?
Hey, you're the one that went off on a tangent. I was merely trying to be helpful.
Gene Kooper, post: 439417, member: 9850 wrote: Hey, you're the one that went off on a tangent. I was merely trying to be helpful.
Your attorney might want to review the facts in light of the circumstance that Intellectual Vagrancy is charged. just sayin'.
I mean, as a matter of charity, I'm willing to believe that everything you post is (in your mind) strictly relevant to the topic under discussion, but I tend to doubt that most judges would agree in the absence of any supporting evidence.
Loyal, post: 439408, member: 228 wrote: Kent,
I think we are talking about different things here. After re-reading some of you posts above, you may be asking a different question than I was trying to answer.
If (as I suspect), you are asking about a simple "one point" calibration using a fugarwe position at the Base, then I suspect (maybe even assume) that Both the Meridian and the Parallel would be the fugarwe position at the Base. I'm sure that there are plenty of these kind of short cuts going on, but it's not something that I run into.
Loyal
Looking at this issue, I will make some assumptions without having any data. The 8000 acres was surveyed using Trimble. The resulting "projection" depends on the date and the software the surveyor had. If it was pre TSO say using Trimmap or GPsurvey then it's probably what Trimble called a plane projection, if it's post TSO it will be a TM projection. Assuming it's a TM projection (or even the plane projection) then there are only two data points to resolve. You need to figure out the longitude of the central meridian and then figure out a scale factor for distances. Using located points on the actual boundary it's not difficult to do this. First principals really.
From there construct an LDP with whatever software you use and you are good to go. The Origin latitude will not be recoverable since there is no metadata but in this case put it near the site and there will be no particular rotational issues.
As far as the old plane projection Trimble used to use, I can say from experience the plane projection and a TM don't play all that well together, although on a small site like this it probably wouldn't show up "much".
If you are using Trimble it's really simple to just do a calibration to the figure created by the deed. Once you have some Lat, Long, heights on the monuments just use the coordinates from the deed description and calibrate to them. You will get a best fit of the deed with all the associated least squares reports the calibration does.
I don't like doing those I would much rather do my own LDP that "fits" the record coordinates as close as is possible, if the site was GPS you will usually find it's pretty simple to construct one that lays over the existing boundary. Then you have all the metadata to have on file and report on your survey. Or you could simply survey it in whatever flavor of canned projection you wish and report the resulting scales and rotations.
