Yesterday's Base Setup

[Shawn Billings]

Yesterday I had a small job to do in a residential subdivision. I've been pretty amazed at how fast I can do small lot surveys by myself. If you had asked me a year or more ago, I would have thought RTK was a poor choice for such jobs. The sacrifice in accuracy across short distances compared to a total station and the limitations posed by typical overhead obstructions on most lots, would be my main reasons. However, I have found the LS capable of a lot of shots that I would have never dreamt possible and the accuracy loss (if there is any) compared to a total station is negligible in my view. The average lot survey requires about 5 hours in field, depending on several factors. Yesterday I finished this small lot in 3 hours. RTK also gives me the ability to tie into block corners and adjoining lot corners easily without any need for traversing, so I end up with more data at the end of the job than I normally would have. This including recovering and tying in five lot corners for my lot as well as three adjoining lot corners.

With a two man crew and total station, I would:

• Arrive at the job site
• Use Locator, Shovel and Cloth tape to find as many corner monuments as possible
• Set up total station traverse points to tie in monuments
• Perform total station survey
• If some monuments were not recovered in initial search, perform calculation to search for missing monuments, stake to calculation, use locator and shovel, set if missing

With RTK and one man, I:

• Arrive at the job site
• Find suitable base location and setup/start base
• Use LS with J-Tip to find first easiest to recover monument. Tie in.
• Use Stake Out or (Distance to Last in Collect) to Stake collected monument, effectively making the LS a tape, to measure distance to next monument.
• Use LS with J-Tip to recover and tie next monument, repeat.

In effect I replace the first pass search, traverse setup, and total station setup with a single pass search and tie, with no regard for visibility to a control point. I'm finding that in most cases I'm as efficient or more efficient than a two man crew. I sacrifice speed in locating buildings. Sometimes I will setup the total station to tie in to buildings but recently I'm using distance/distance intersection with 4' offsets to building corners. I've been able to produce very accurate results this way, and while not as fast as a two man crew, the savings in time in all other aspects of the survey make up for the somewhat slower building ties.

As I mentioned above, finding a suitable base point is my first order of business. I have used Javad's method of putting the base on the work truck. Works well, but I thought that I might need to move my vehicle on this job at some point so I opted against that. Instead I noticed the brick mailbox had a flat top, so I put it on the mail box. I left the radio in the truck parked next to the mail box.

 

[Darren Clemons]

Great write up Shawn, thanks for sharing. We've basically come to the same conclusion you have on residential lot surveys. Javad makes them much, much more feasible for one man than any of the "other" GPS systems we ever had. The buildings are the most difficult. We've tried the offset using set bearing by compass but it's tricky with calibration needed on most every site. Your offset method is what we've went to mostly as well. I had never thought of putting a base in such a spot, I still am stuck on having to have the nail or pin in the ground to set on but it's not really needed.
Only thing we do nowadays is with the world files and digital mapping so good, we will punch in 5 or 6 surrounding lots and have around 20 or so design points that are in my selected state plane coordinate system when we get to the job site. We rotate the "old" plat bearings to the digital mapping NOT using the plat bearings so we're pretty much on grid bearings when we get there. It's usually easy to do this with road center lines or visible property lines and such. As soon as I start base I can usually stake to within 3'-5' or so of any lot corner. As soon as we find the first one, we "move" the entire batch and then off to the second. Many times we're so close on bearing using our maps as a guide we don't even need to rotate or anything like that IF we find all original corners. Of course, usually some are missing and we'll snap and rotate accordingly to reset any of those.
Oh, and I can't find my first corner with my Jtip like you did but I'll be able to soon. Mine has shipped and will be here Tuesday! Can't wait to try it out.

 

[Shawn Billings]

I don't miss wagging around a metal locator one bit, Darren. As a solo guy, the J-Tip makes a LOT of sense. For a two man operation, it's still nice I'm sure, but for a solo guy, freeing up a hand is a very big deal.

Now when I do my corner search (which is also when I do my corner ties), I have the LS with J-Tip, my trusty, heavy-duty folding NATO shovel, a 25' tape in my vest pocket and a deed sketch or copy of the plat. As needed I also have a machete or loppers depending on the job. Not having to keep up with a locator with all of the other stuff is really nice. I don't have to carry it around and I don't have to remember to pick it up when I move to the next point.

Regarding RTK for residential lot surveys, I was almost embarrassed to mention it. It seems odd to do such small jobs with such a powerful tool, but it works so well at it. The biggest advantage to me is the ease of tying in multiple corners from adjoining tracts. Last week I tied in an adjoining tract corner that was over 3000' away. It took an extra ten minutes. By traversing along the roads it would have taken a couple of hours or more. I also went 1500 feet in the other direction to tie in a few offsite adjoining tract corners that way. Took me an hour to grab an extra 5 or so corners (mostly due to search time). It simply would not have been practical to do this by total station or by post-process static GPS and total station methods.

From a business standpoint, this is how you build a database that is truly valuable.

 

[Adam]

I did the same 14 acre boundary twice this week. Once with LS, I had a found corner that didn't check very well. About 3 ft out from where the math put it. I had found all the other corners, all were capped and undisturbed far as I could tell. It was in a crappy area so Tim traversed around to it tying corners as he went. Most of the corners were checking a couple hundredths. The farthest out was .12. It took me 3 hours to do it with the LS and I picked up a bunch of fence locations with it. When tim traversed he only shot the corners for check and it took about 6 hours. If there is something funky going on I like to check it old school and never have I found a bad shot when I allow J field to do its thing and run thru the minimum criteria that I have set.

 

[Shawn Billings]

I've been thinking about that since you mentioned it the other day. Do you suppose the previous work that established the monument that was off by 3' was done by RTK?

 

[Adam]

I've been thinking about that since you mentioned it the other day. Do you suppose the previous work that established the monument that was off by 3' was done by RTK?

I don't think so, but I haven't dug that deep yet. From my experience in the mountains, no one works in the woods with GPS unless they have an LS.

 

[Nate The Surveyor]

Shawn, I know someone that used to drive a piece of 5/8 all thread into the top of a post and that was his base station I suppose I could do the same thing with some quarter inch. Cut it off, with a hacksaw, after driving it, to remove the mangled top. Then lightly tool it with a flat file.

 

[Shawn Billings]

Shawn, I know someone that used to drive a piece of 5/8 all thread into the top of a post and that was his base station I suppose I could do the same thing with some quarter inch. Cut it off, with a hacksaw, after driving it, to remove the mangled top. Then lightly tool it with a flat file.

I don't mind setting a nail and setting a tripod over it for jobs that may take more than a day, but for these that I know I'll finish in under a day, it seems like overkill. You remember when we were at the Arkansas convention last spring and we set the Triumph 2 on a retaining wall and set the radio down next to it?

Last week, I did a small one and didn't want to take the time putting the radio antenna on a pole, so I just set it in the grass next to my base setup (which was on a tripod). The ground plane kept the antenna upright.

I have though of what you are talking about Nate. Probably be more efficient to have a nut of some sort to put on the top of the bolt so that when you hammer it in, the threads don't get burred to begin with.

 

[Adam]

Shawn, I know someone that used to drive a piece of 5/8 all thread into the top of a post and that was his base station I suppose I could do the same thing with some quarter inch. Cut it off, with a hacksaw, after driving it, to remove the mangled top. Then lightly tool it with a flat file.

Only thing is how you know a bull ain't backed up and took a good scratching at the post which is probably in tall grass so you can't see the bottom to judge for movement?