I recently posted a picture of a setup where I needed a tripod to hold up one leg of another tripod, in order to get the antenna nicely above the surroundings.
Another way to do that would be to fabricate a longer tripod leg, say by taking an 8 ft board and using a router to cut the groove on each side. If I did that, would a common pine or fir board be be stable enough for a few hours?
I have potential target for a GPS on Bench Mark program session, shown in the picture below, that needs a tall setup. It seems likely there may be metal in the walls of the building, and certainly equipment inside. I expect I could get away with being close to the RR because it is at a public crossing. That could use a tall tripod, say by making three of those longer legs, in order to get above an obstacle. Stepladder for setting up the tribrach. At that height, the horizontal centering might not be too great, but vertical is what is critical.
Or should I get a friend with a lathe to thread fittings for a piece of EMT conduit so I could have a fixed-height (say 2.5 meter) pole? I'd have to acquire a good rod level, of course. How do you get an 8+ ft pole that is top-heavy with an antenna to remain vertical for several hours?
Since this is a hobby activity, the budget is "as little as possible." Manufactured poles might break the budget.
Bench mark target:
We use range poles to elevate receivers. They can be had for less than $30 for four foot sections. Making sure it is plumb and doesn??t move too much in the wind might be tricky.
What we do probably seems crazy to most you guys but it works great for us. We have a 5/8? stud welded on to a trailer we take to our job sites. We use the range poles to get the receiver up in the air over the trailer. We never set up on known points and collect opus data daily so all we really care about is that the receiver stays in the same spot from day to day for the duration of the job. Not that setting up a tripod is too difficult but this is a lot quicker and anyone can do it. It is surprisingly consistent this is six days of opus solutions with the receiver being taken down every night.
8' length of 1" black iron pipe. You'll have to adapt a point to a pipe cap on one end and a 5/8"-11 stud to a pipe cap on the other, but that's not hard to do if you're careful. Use a regular tripod and one of those plastic clamp adapters to secure the rod. Plumb with a rod bubble or a theodolite. Easy to come by and cheap enough.
I use a similar arrangement for my UHF antenna mast. It fits in my truck and gets the antenna high enough for most work. The only differences are that I didn't bother to carefully center the point (all it does is anchor the bottom end in the ground) and I have a custom adapter for the UHF antenna instead of a threaded stud.
I am interested in whatever solution you come up with. I have run into similar situations where I tried to use a taller rod but it just wasn't stable enough for the given wind conditions. I thought about night observations during calmer winds. But I was still uncomfortable with the setup. I also thought about a taller tripod or bipod to provide stability higher up the rod.
It also occurs to me if you are only after vertical, why not set a nail away from that building where you have clear skies but within one level setup distance from the station?
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Having an extra long leg or legs can solve difficult setups.
I use a 4ft section of aluminum pole to put on top of tribrach setups to reach 8+ feet.
Using a 3 legged pod and using all my pole extensions I can go up to around 19ft and have had to tie 40lb test braided fishing line to anchors before to maintain a setup in the wind.
On critical setups at that height I recommend using a TS to check plumb.
I've never done a high rod for a control point or a static point, with the exception of a few bench marks where I needed to set up something unusual and didn't really care all that much about the horizontal.
For RTK shots I have an extendable rod, if it won't do it then it's time for the TS.
BushAxe, post: 453371, member: 11897 wrote: why not set a nail away from that building where you have clear skies but within one level setup distance from the station?
That would be the easy way to make use of the disk for your own project, but there's no way to tell the OPUS Share process about such operations so you end up with an invalid horiz position in the data base.
As far as I can tell the GPS on BM program has to have the antenna over the mark.
I had thought about such methods for a vertically mounted disk, where the ARP could be set to the same height as the mark by using the level to direct the adjustment of the antenna tripod and tribrach. But if you tie it to the PID and then note that it isn't over it, I doubt NGS would use the data for their model checking. Is there anything written about doing this for GPS on BM?
Bill93, post: 453405, member: 87 wrote: Is there anything written about doing this for GPS on BM?
Not that I am aware. I am not very familiar with the program.
Bill93, post: 453405, member: 87 wrote: That would be the easy way to make use of the disk for your own project, but there's no way to tell the OPUS Share process about such operations so you end up with an invalid horiz position in the data base.
As far as I can tell the GPS on BM program has to have the antenna over the mark.
I had thought about such methods for a vertically mounted disk, where the ARP could be set to the same height as the mark by using the level to direct the adjustment of the antenna tripod and tribrach. But if you tie it to the PID and then note that it isn't over it, I doubt NGS would use the data for their model checking. Is there anything written about doing this for GPS on BM?
In the old days when we set a range pole for a number of days we ran guy wires. It seems with Jims idea that you could fabricate a ring with holes and anchor a tall pipe to hold it still even in a moderate wind.
Bill93, post: 453405, member: 87 wrote: That would be the easy way to make use of the disk for your own project, but there's no way to tell the OPUS Share process about such operations so you end up with an invalid horiz position in the data base.
As far as I can tell the GPS on BM program has to have the antenna over the mark.
I had thought about such methods for a vertically mounted disk, where the ARP could be set to the same height as the mark by using the level to direct the adjustment of the antenna tripod and tribrach. But if you tie it to the PID and then note that it isn't over it, I doubt NGS would use the data for their model checking. Is there anything written about doing this for GPS on BM?
It would be unfortunate if that's the only way to do bench marks for modelling, there are lots of good ones on the sides of buildings, wing walls of bridges, under trees, places where GPS isn't very usable. The horizontal location isn't all that important for GEOID modelling, a foot this way or that won't make a bit of difference. It's the elevation and height that matter more.
The scanning world has some 'portable ' rods that extend a good 20 or 30 feet with stays / anchors and a scanner on top. I have not reviewed to see about plumb or getting over a specific point.
We have a 25 foot aluminum rod. That top section is mighty shaky with a prism.
A tall rod would tend to oscillate above the reference point. Nothing to really worry about as the GPS solution is a meaned position.
I have used a 12' adjustable rod, steadied by a three legged bipod. I have also used up to 3 of the upper half sections on my standard three legged bipod GPS setups for a height of almost 6 meters. I have set up a tripod and used multiple top halves of GPS rods on a tribrach adaptor. Lastly I have based an extended rod for a GPS antenna using my megalapod approach, which is two bipods on one pole for a total of 4 legs, once setup up, tricky, it is rock solid.
Paul in PA
