These used to be very common. Now can barely find them. Anyone have an old one lying around that they'd like to part with?
Why?
do you live in Kansas?
Why?
Good question. I am experimenting with the idea of mounting ProMark3 gps receivers on top of the prisms and simultaneously collecting GPS file and being able to shoot the point with total station. Having a tilting prism will throw off the position of the gps receiver considerably, while the lack of tilting function will not considerably distort the slope distance measurement. Topcon's fixed single prism is perfect for this application.
Why?
I use them like that too (the fixed prisms have a 5/8s thread on top with a candy cane). I inherited them though; not my choice for steep work. On steep sights they can be up to 2 hundredths off which doesn't matter for small stuff but a mile of traverse in rough terrain with short sights due to vegetation and hill breaks (can't see through the dirt) it starts to add up.
Next rough forest traverse I'm either going to borrow a couple of tilting targets from my co-worker or use two of my personal ones that I own.
Why?
Exactly, Dave. Thank you. One question about your suggestion of using tilting prisms for steep work. I have several tilting prisms in my arsenal already. However, let's say you're doing that steep forested tract and you use tilting prisms. In this case if you mount gps receivers on top of the tilting prisms won't the gps solution become considerably distorted? Is your thinking to make the prism observations first priority and the gps observations a second level of information?
Why?
I don't use GPS for the most part in Forest work because there is almost no open sky other than directly overhead. I am lucky to get 2 or 3 SVs. So it's not a problem for me. Besides the tilting Topcon or Seco prisms don't have a top nut.
If I wanted to do it I would have to have some sort of mounting bracket with a tilting prism inside it and a centered bar on top. Sort of like instead of having a U shaped yoke; have a rectangular yoke.
Dang that reminds me; when I talked to our adjoining land owner the last time I was out in the Forest I forgot to ask permission to set a couple of GPS control points in her big open pasture. All of the State property is heavily forested but the adjoiner has a big open pasture that would be good to georeference my Survey. I'm sort of walking on egg shells with her because there are some sensitive issues going on so I don't want to launch a fight by just doing something like that without permission. We have a right of entry which I am using for traversing the boundary and of course finding and tie-ing boundary monuments but setting control monuments on private land may be a questionable activity without permission and even if it is legal I still don't want to unnecessarily irritate what has been a cooperative adjoiner so far.
Why?
I put a Sokkia fixed prism under my antenna. It is aluminum with a 2 1/2 inch prism.
This setup on a monument for back site while my instrument is over a hub (already collected while clearing around this monument) to tie into another monument.
Next setup was near 4,000 ft to north.
Why?
Thanks for that photo and description. Yes that is very similar to what I'd like to do. I have seen those prisms. I think they might be made by Omni, and I'm not so fond of the Omni prism. They just seem inferior in terms of quality of construction. But, yes, that's the idea. And while I had been envisioning mounting the prism/antenna combo on top of a tripod/tribrach/adapter, your photo makes it clear that the same can be done on a rod. I suppose you use the rod pictured with a bipod?
Why?
The Sokkia style is more available. The Topcon fixed prism holder I remember was thin plastic.
Picture is of my typical rover rod setup using a 3leg bipod.
Will also put on top section of a two meter pole on tribrac and tripod over control points for longer sessions.
With our rolling hills and abundance of canopy, an extra 3 to 4 feet of antenna height helps reception.
Try this assembly. It only has a 25 mm prism, but it is tiltable.
http://www.surveying.com/products/details.asp?prodID=6405-01-FOR
Phil, great suggestion. I think that's what Dave Karoly was basically suggesting. I assume the yoke which contains the prism has 5/8-11 threads, top and bottom, and thus could be outfitted in a variety of ways with adapters etc. . I'll check this product out further. Thank you.
Why?
I've read that in several places, that extra antenna height will aid in reception.
Yes, the yoke does have 5/8 X 11 threads top and bottom. They do come up on Ebay occasionally.
