Shawn Billings, post: 407762, member: 6521 wrote: I think that Trimble's "calibration" is synonymous, but would appreciate any definitive evidence to the contrary.
Trimble had it set up so you had some choices, calibration has been strictly a process to merge GPS data to existing control, you basically locate as many points as you want and it will calculate the "errors" it sees and gives you a report for each point located, then you get to accept or reject and apply the calibration, throw out points, keep some, it is a process that can be done in the field with RTK or in the office with RTK or Static. At one time it was even taught to do a calibration AFTER a Static control adjustment.
I don't like it much, it never made any sense to do it unless you just didn't have any choice, but if I do have to do it I want to sit in the office and use Static numbers.
You could also do a no datum, no projection, I never liked that choice either, I do know some that used it and there were/are issues with it, I don't think for most users it's doing what they think it's doing.
At one time you could do a plane projection which was what I USED to do, that is basically what I THINK is a one form of localization in Leica speak.
They quit allowing the simple Plane projection about 2000 with the advent of TGO, since then you need to project on a Transverse Mercator system, allowing you to do your own local LDP which I think is another form of what is sometimes called a localization.
There are also options to do a datum shift, apply a subtraction or addition to coordinates and to elevations, you can also rotate, possibly to simulate state plane bearings. There are many ways to mess up a coordinate system by pushing buttons.
MightyMoe, post: 407781, member: 700 wrote: There are many ways to mess up a coordinate system by pushing buttons
AMEN!
MightyMoe, post: 407781, member: 700 wrote: Trimble had it set up so you had some choices, calibration has been strictly a process to merge GPS data to existing control, you basically locate as many points as you want and it will calculate the "errors" it sees and gives you a report for each point located, then you get to accept or reject and apply the calibration, throw out points, keep some, it is a process that can be done in the field with RTK or in the office with RTK or Static. At one time it was even taught to do a calibration AFTER a Static control adjustment.
I don't like it much, it never made any sense to do it unless you just didn't have any choice, but if I do have to do it I want to sit in the office and use Static numbers.
You could also do a no datum, no projection, I never liked that choice either, I do know some that used it and there were/are issues with it, I don't think for most users it's doing what they think it's doing.
At one time you could do a plane projection which was what I USED to do, that is basically what I THINK is a one form of localization in Leica speak.
They quit allowing the simple Plane projection about 2000 with the advent of TGO, since then you need to project on a Transverse Mercator system, allowing you to do your own local LDP which I think is another form of what is sometimes called a localization.
There are also options to do a datum shift, apply a subtraction or addition to coordinates and to elevations, you can also rotate, possibly to simulate state plane bearings. There are many ways to mess up a coordinate system by pushing buttons.
You have to think more in the vertical mode on a construction project to see what the Trimble Calibration is most used for. You get a stakeout job designed from whatever control was initially set, correct or not. In order to stake or use machine control to move the dirt, you need your GPS to be tied into that control. Horizontally is usually not going to be a big deal on a dirt job, but the vertical is. You check into the control points first to see if they are all in agreement with each other to whatever tolerance you need, then do a site calibration to the ones that are good so you are working on the same vertical datum as the original control. If the control doesn't agree within itself, you've got to fix that issue before you calibrate to it.
eddycreek, post: 407793, member: 501 wrote: You have to think more in the vertical mode on a construction project to see what the Trimble Calibration is most used for. You get a stakeout job designed from whatever control was initially set, correct or not. In order to stake or use machine control to move the dirt, you need your GPS to be tied into that control. Horizontally is usually not going to be a big deal on a dirt job, but the vertical is. You check into the control points first to see if they are all in agreement with each other to whatever tolerance you need, then do a site calibration to the ones that are good so you are working on the same vertical datum as the original control. If the control doesn't agree within itself, you've got to fix that issue before you calibrate to it.
I agree, calibration was a way in the early days to simulate elevations with GPS, the main problem with doing one for elevations is that it forms a plane, for very small sites it's ok, but once the site gets very large, it can create problems. A small airport, would be one example where I have used it and been very frustrated. Much better results are achieved using a Geoid Model.
