And it is leaning 10°, how much error is introduced, into the horizontal position?
The Antennae is on top of a Wild Quick release.
As I understand it, the actual "Antennae" is several inches ABOVE the GPS antennae, projected like a ghost.
I guess I could test it... with a long static shot while plumb, and then lean it and see. But, these are specs... and should be knowable.
I have Leg Ant, from JAvad//Topcon.
Thanks.
Nate
Nate,
You are kidding right? or better yet, for which error are you looking?
I am serious.... I am working on a project, that will require the antenna to be cocked at some angles....
And, it is not normal...
And, IF the 'center' of the antennae is really a ghost projected UP about 6" above the antennae phase center, then cocking it some, will introduce some error... and I need to keep "Track" of it!
Nate
I hope, for your sake, that Loyal chimes in soon, but it appears to me that the electronic center in within the unit for your purposes.
Was that the right diagram for your unit? Did you peruse the OPUS site?
0.5 ft * sin(10 deg) = 0.087 ft sideways
0.5 ft * [1- cos(10 deg)] < 0.001 ft vertical
You need to find out the antenna phase center (APC) for your antenna. Are you using this as a base station? If so you can process from the APC rather than the antenna reference point (ARP) and not have to take into account the leaning. Try to keep the ground plane as level as possible even if you cannot get it over a specific point.
Peter Lazio
>process from the APC rather than the antenna reference point (ARP)
I would expect the processor to use the vertical difference between these, but not have a way to enter a leaning angle. Does it?
Why not just set remote points with a torpedo level about that far away and shoot them to get grade and calculate true position by dist and dist.
Seriously?
Bill,
If the software is provided a coordinate for the ARP the software computes the coordinate of the APC. This is usually simply the vertical difference from the APP to the APC. All processing is done using the APC coordinates. After computing the baseline the end of the vector is transformed from APC back to the ARP.
If you specify the coordinate of the APC there is no need for this transformation.
Peter Lazio
But I'm still not sure of the answer to my question, does the transformation assume vertical or does it allow for a tilt angle?
This sounds more like a “procedure” question, than a technical one.
Instead of dinking around worrying about ARP(s), APC(s), Angles, offsets, and and the FACT that a “tilted” antenna will screw-up your mask-angle...
Simply do what I do with Bearing Trees (similar to what Mr. Harris suggested), and measure (say) 10, 20, 25 ft. from said Fence post (or Bearing Tree) to three points separated by ~120 arc degrees from the center of the post (BT). You can do this solo by using a pocket full of ROMEX-staples and a pocket tape.
Then simply drop the data into a CAD program, and snap a few circles in there to intersect.
The internal computations in all GPS measurements boil down to the L1 Phase Center, and “tilting” the Antenna screws with the “mask-angle,” so DON'T DO IT!
In the case of a “tall” Fence post, or a PLSS Bearing Tree (can't put the staple in the CENTER), simply record the approximate diameter of the post/tree, and pay attention when you look at the data in CAD.
Loyal
From the normal measure point to phase center should only be a few mm (2 to 4 maybe).
If the RTK Antennae is set on top of a tall fencepost- Nate
I'm still wondering under what circumstances it becomes necessary to tilt the reciever? I think that's what you're asking; right? If the fence post is leaning then you hold the staff perpendicular and rest the reciever on top, if that's where you want the shot, or at the base if that's where you want it.
Why are you tilting the antenna?
Natester
No ghosts involved in this at all. It's just pure measurements from the ARP to the APC. Nothing hard about that. But how will you figure out the bearing of the lean? That is the crucial thing that you cannot figure out easily. The vertical is easy, but the horizontal is not. AND...and this is the important AND.
Loyal has it right though. You lean the antenna 10 degrees and your mask will be entirely screwed up. You could set the unit to a zero mask for gathering but then you would have to really do a lot of work in the post processing to see which ones to remove and which ones to use based on the skyplots.
And it's really not just your mask. The NGS has calibrated your antenna based on a stable and horizontal setup. Not some out of plumb science experiment. I would think a lot of the background processing is assuming that you had a plumb instrument. It calculates your position then applies the slope angles of the SV"s along with all the other things to derive a position.
No telling what you are mucking around with when you toss up a faulty setup.
Agree with others. Measure it in from someplace else and then shoot that point.
So why do you need to have a setup on a leaning post anyway? That baffles me.
Deral
Javad advertises
That with the umbrella option, that a plumb set up is not necessary.
There more reasons than this, but this is one reason for the question.
Nate
Javad advertises
Natester.
I got to touch one at the ESRI conference. It has two cameras and one of them faces downwards. Interesting, but Javad has always been that. Very smart man.
The camera supplies the offset to the point. I'm waiting on a review.
The doctor though is just a monster when it comes to the science of all this. I doubt that he would be wrong.
Deral
It was NOT the unit with four receivers. It was a single unit that looked like a camera.
The National (NGS) CORS site at Winnfield, LA (WNFL) is actually on a fence post.
Oops. That's < 0.01 ft vertical
If the RTK is HyJacked
Welcome back Professor Mugnier, it will be great reading your posts again.
Have a great day!
Radar
