gps measure up = antenna height
I would not call it a sloppy practice.
It does however restrict the possibility of using precisely the vertical component of the data. There could be applications where purposely choosing to ignore the HI would a preferred choice. Not sure in which case, but there could be, who knows?
I would call it more a "limitative practice", but the word limitative does not exist... You get the idea anyway.
gps measure up = antenna height
Over the years this question has come up a number of times. We have run tests to see just what will happen using RTK and changing the HI. I've never used our units much over 6 miles so that is the limit of my tests. There is just no measurable difference in XY coordinates when the HI is changed. Now, if you are doing a static or OPUS session it might make a difference. By using a CORS station 250 miles from your receiver I could see it being a problem. That isn't something I've ever looked at.
So, for short distances do you need to always measure up to get good XY coordinates?
No.
Not that I advocate ignoring HI's, but it's not going to change your XY if you input 5' for an HI when your rover is 2 miles from the base instead of 8.5' or 0' for the HI.
My advice would be to pay close attention to antenna heights and run some tests of your own to see what changing them does to your data.
No, Use a fixed height 2 m pole and keep the rod height fixed in the data collector and forget about it.
gps measure up = antenna height
If you can't bring yourself to measuring HI's, I suggest, instead of leaving it at 0, you put in an even estimated foot. That would eliminate any minor error in the x/y coordinates.
Yes.
With my software you have to enter some distance before it will initialize the base...might as well be something real.
i use a fixed height tripod and fixed height range pole, so I never have to change the defaults in my setup.
Andy J
i use a fixed height tripod and fixed height range pole, so I never have to change the defaults in my setup.
How would such a setup work? Can you expand on that tripod and it's source, a range rod is usually 4 feet so that is easy to picture in the mind? How you could have, a fixed height tripod baffles me.
jud
Andy J
here is the NGS suggested data.. they take a bit of getting used to, but the tad bit more time you spend setting up MORE than offsets the time measuring up, re-checking etc.
http://www.ngs.noaa.gov/PROJECTS/GPSmanual/equipment.htm
I have been having this argument for 25 years now. It doesn't matter IF you don't care about elevations. The first time this came up I was at Edwards AFB in California, and we were aligning radar antennas, determing the azimuth of reference objects. They did not care about elevations. I had a bunch of EE's helping me, so the HI's were all messed up. It didn't matter.
I often use temporary bases when doing photo/lidar control. I use an HI of zero. This gives me a position and elevation of the base of the antenna. Now, unless I am REALLY high above the ground, and there is some serious deflection of the vertical, the position is the same as if I had measured down to the ground.
Think of a CORS on a tower (as many of them are). Does anyone think the position is wrong because they didn't measure the distance to the ground?????
Andy J
Those who follow the cookbook and those who have spent a little time thinking about what they do and what their equipment does, often will disagree on such things as using the HI for horiz points, I put HI in the mix because it is asked for in my post processing software, not because I think it has any real value in improving the Lat. and Long. positions, if somehow the HI is not noted in the field book, not a disaster, nor am I compromising anything by using an approximation of that missing measurement in the software entry for the position, even if that calibrated gestiment is off by feet. Had an old USACE inspector tell me that speed and thoroughness in collecting survey data was not accomplished be trying to hurry and taking shortcuts, it was done by choosing good complete methods and doing everything that same way every time, that created an unconscious mental check list in your mind that would shout, tilt, if something was left out because of a distraction. So, if your doing any work where that HI has an impact on your results, then make it the habit to measure that HI every time, needed or not, just part of imprinting good technique in your mind.
jud
Andy J
Thanks, kind of like the old center leg Kern Tripods we used in the past, except the center leg was adjustable on them. Was not thinking center leg, was thinking 3 nonadjustable legs, with only one opining position, could not figure that out unless every setup was on a perfectly flat surface. Not needing to look through a scope, a non adjustable center leg should work fine.
jud
YES.
I'm a bit surprised that none of you guys suggested that if you didn't use a measure up there would be no chance of finding a blunder through the use of redundancy i.e. observe a vector more than once!:-|
A CORS has an antenna which is permanently affixed to the monument.
On the other hand, a typical passive control monument I set will have a different antenna height each time I set up (I don't use fixed height tripods). I suppose if I just guessed and always put in 5' it wouldn't make a lot of difference but I just can't do it that way.
I always measure accurate HIs, HTs and Antenna Heights; I think it is just good practice to do so.
gps measure up ''Every Time As Well As Always''
A GPS position always has an up value because the default coordinates are XYZ. If you do not have a good vertical elevation on your Lat Lon or SPC and you reoccupy that point with GPS on another day, you can actually move things horizontally. Drove me crazy for a day trying to get a network solution. I had all the correct measure ups of field data sheets but incorrectly entered one wrong.
Paul in PA
Pretty Amazing........
.......an entire thread by people whose careers and businesses depend upon taking accurate and comprehensive measurements discussing whether or not to shirk off taking one lousy ruler reading.
:-/ 😛 :-O :-S
Pretty Amazing........
> .......an entire thread by people whose careers and businesses depend upon taking accurate and comprehensive measurements discussing whether or not to shirk off taking one lousy ruler reading.
>
>
> :-/ 😛 :-O :-S
It's what people in the surveying "industry" do.
Pretty Amazing........
Well, you bring up a good point. How many surveyors have enough education in geodesy or in even using GPS equipment? How many surveyors use GPS on a regular basis?
A real "professional" would get the training or expertise s/he needs, but how many do?