Would you get from a GPS mounted on a 4 wheeler going 15 mph? A colleague caught someone doing this and we seem to think the results wouldn't be that good.
It depends on the process that you're using... We do something similar, mounting a GPS receiver on the side of our survey vehicle. We set the receiver to take an observation every 50 meters. We drive at regular highway speeds (55 mph). We do post processed kinematic and we see errors around 0.5-1.0 feet after performing a network adjustment using NYSNet CORS base data. About 40% of our data (initialized/locked) is useful. So it all depends on what you're using it for and how you're processing it...
Disclaimer: I may be recollecting this process/numbers incorrectly as I'm not the one performing the work, but this statement is based on overhearing the results explained to the department that requests this work.
I should have specified, this is for a topo and it is across pasture.
Tommy Young, post: 375109, member: 703 wrote: I should have specified, this is for a topo and it is across pasture.
I guess it depends on the terrain. We have had good resaults riding topo with atv's. I don't know if we were going quite 15 mph though, probably 10 at least. If there are breaks we slow down or grab the rover and walk them.
Tommy Young, post: 375106, member: 703 wrote: Would you get from a GPS mounted on a 4 wheeler going 15 mph? A colleague caught someone doing this and we seem to think the results wouldn't be that good.
fantastic results.
I wouldn't publish if the site wasn't driven in overlapping patterns and a post drafting site walk done. SPP auto topo has its place but demands it's own style of QC.
We get great results using a Polaris Ranger but we're driving slower than that. I don't think the speed decreases the precision, I just think it makes the ride too bumpy and you end up with too much vertical movement of the antenna. We use one of these:
http://www.surveying.com/Products/GPS-and-GNSS-Survey-Accessories/Vehicle-Accessories/5114-40-01
thebionicman, post: 375114, member: 8136 wrote: I wouldn't publish if the site wasn't driven in overlapping patterns and a post drafting site walk done. SPP auto topo has its place but demands it's own style of QC.
The nice thing about doing auto topo is that you can get as much data as you want... set it to record every second or every foot and drive to your hearts content. As flat as it is around here, outliers are pretty easy to spot in the TIN if you have enough data.
Edit: I don't actually have my guys doing 1" or 1' intervals lol. Usually 10'.
It depends on the site, not normally 15 mph, but across a flat open field that would be ok.
It also depends on the site how you set up the collection, sometimes it's best to do every 25', sometimes every 5 secs.
If you are running out broken Breaks I prefer every 5 seconds, go slow along them and be sure you get each turn.
But for dirt topo, a 4 wheeler/GPS can't be beat unless you can fly it.
Wouldn't do it for concrete/pavement/building work.
MightyMoe, post: 375122, member: 700 wrote: But for dirt topo, a 4 wheeler/GPS can't be beat unless you can fly it.
Wouldn't do it for concrete/pavement/building work.
I know of a fellow that topo'd the runway at the Nashville International Airport with a GPS mounted to a 4 wheeler.
I don't know about all that.
MightyMoe, post: 375122, member: 700 wrote: It depends on the site, not normally 15 mph, but across a flat open field that would be ok.
It also depends on the site how you set up the collection, sometimes it's best to do every 25', sometimes every 5 secs.
If you are running out broken Breaks I prefer every 5 seconds, go slow along them and be sure you get each turn.
But for dirt topo, a 4 wheeler/GPS can't be beat unless you can fly it.
Wouldn't do it for concrete/pavement/building work.
You can also use a servo total station to do the same thing if you drive slow.
Tommy Young, post: 375126, member: 703 wrote: I know of a fellow that topo'd the runway at the Nashville International Airport with a GPS mounted to a 4 wheeler.
I don't know about all that.
yeah, that is not a good idea, after working with FAA regs, I wouldn't even think of doing that.
I also wouldn't walk it with GPS, wrong tool for that.
Tommy Young, post: 375106, member: 703 wrote: Would you get from a GPS mounted on a 4 wheeler going 15 mph? A colleague caught someone doing this and we seem to think the results wouldn't be that good.
I wouldn't personally. I walk it all the time just gives me more confidence in what I am producing.
MightyMoe, post: 375151, member: 700 wrote: yeah, that is not a good idea, after working with FAA regs, I wouldn't even think of doing that.
I also wouldn't walk it with GPS, wrong tool for that.
That is what I was gonna say. He may have Topoed it, but not to FAA spec.
What I've found is if the antenna is on a mast, it gets whipped around. And the antenna will be subjected to greater than 4G acceleration. And cycle slips.
By spec 4G is an upper limit to prevent unauthorized (extra-military) uses.
We use the one I posted above with no problem; however, in addition to the two U-clamps provided, we bungee it tightly to the upper part of the roll cage. You don't want to go any higher than you need to with it.
Going slower would be better. I did 20 acres before lunch one day. This included about 5 check sections and a few break lines that we walked and took shots with a fixed height pole. This was a one foot topo. I would never recommend this for all sites or projects. It is just another tool in the tool box.
Larry Scott, post: 375232, member: 8766 wrote: What I've found is if the antenna is on a mast, it gets whipped around. And the antenna will be subjected to greater than 4G acceleration. And cycle slips.
By spec 4G is an upper limit to prevent unauthorized (extra-military) uses.
Are you saying that the 4G acceleration limitation is something built into the civilian GPS signal?
That is one of several safeguards built into civilian receivers to prevent them from being used for military purposes. My understanding is that there are limits on acceleration, velocity, and altitude.
I stay around 3-4 miles per hour using my gator. As others stated, much faster and the ride gets to bumpy.