Surveyor's Footsteps: How Close Is Close Enough?
If you work for the Army Corps of Engineers, never say something’s “Good enough for government work.” It’s doubtful the Corps will find that humorous. Though it was 40 years ago, I still recall the remark, but I’m not sure which one of us said it in front of the Corps supervisor.
For the most part, the Corps were good to work for, up until the allotted funds were used up. For the three crews and the supervisor my employer had contracted to provide, it appeared we would have plenty of work until the spring. It was three weeks before Christmas, my wife was seven months pregnant and we lived in rural Missouri when our company was notified we had one more week of employment. We were assured there was no reason to worry; Congress will allot us more money in the new budget. But, when spring came and the company called me back to work, I had already found a new job with better pay and opportunities so I did not return.
The reality of working for the Army Corps was, it was the most precise work our company had ever performed. “Good enough for government work” was actually our very best. It was unfortunate we chose to joke about it in front of our government supervisor. Throughout the experience, we learned quite a lot about how to be accurate using proper procedures. I wonder if anyone today uses the kind of control points we ran cross country – the shortest a traverse leg must be was at least 1,600 feet and level run turns had to be within 3 feet of the back sight distance.
After we turned in our field work, the Corps would “adjust” our work so that it was more accurate. I would think that the company supervisor of our three crews wished he had been able to sit beside them as they crunched the numbers. To my knowledge, all of our crews gave a good day’s work, were given top-quality equipment to use and were well compensated.
A few years later, I was back on the East Coast and running a crew of my own. The transit man, Charlie, said he had two speeds: wrong and accurate. I never did seem to speed him up, but he sure was precise. How precise? Here’s one memorable example:
While performing a large boundary survey of a tract that bordered Valley Forge National Park, we used a 200-foot tape and probably a 20-second transit at best. (The transit I went into business with has a 20-second Vernier.)
One of the best things about employees is having them do an occasional task that requires heavy lifting. While Mike was up in the attic putting an old computer into my electronics repository, he found something. Arriving back in the office, he said, “I saw a wooden box up there with an old instrument in it. Can I bring it down here and put it up on the file cabinet?” I dusted it off and found a magnifying glass. Thus, I can now repeat, I have a 20-second transit. It is actually surprising it has such precision.
Getting back to Charlie and his precision, Charlie took his time turning up sets of angles, and we implemented slope chaining. Using a 200-foot chain, you can slope out 200 feet from the gun, and on the next set up, slope 200 feet back from the gun. Between chaining points the plumb bob measured the horizontal difference. I know we had a great closure on that survey, and would probably feel proud of my excellent chaining work, but all I recall is that Charlie’s “sets” with their five-second interpolations did add up to five seconds from a perfect angular closure. I was sure to tell him immediately just how precise he had been. I was astonished.
Few people today “chain” distances. I doubt party chiefs under the age of 35 understand the hieroglyphics in the field books and know why they are there. Taking a field book off the shelf, I could see how I used the cosine to convert my slope chain 200 feet to a horizontal distance. On the extra pages of a field book was much information at the fingertips of a party chief circa 1980.
I have retraced surveys back to 1900 that closed just as precise as our Valley Forge National Park traverse and I was following them up with a total station. Yes, there are times when compensating errors produce what appears as an excellent closure, but generally, when we use good procedures we all get good results.
Today, I was bringing my field control survey into a 12-year-old CAD drawing created by a company in whose work I have little confidence. Why don’t I have confidence? My last interaction with them was 15 years ago (yes, I realize some people do change with time). But, I had prepared a boundary survey for the engineering firm and they phoned to ask about my inaccuracies. It took some time to explain to the engineer who was preparing the subdivision plan, that 0.001 feet was from rounding and it did not make any difference. My computer printout was set to three places, so the fourth place rounded. This “error” was at the point where the right of way line intersected the property line. I backed away from them and moved on to survey greener pastures. Thinking about it, the coordinates may have been off by 0.0001, but what’s the difference? Was it “close enough?”
Comparing my recent work with this recent CAD plan, there was a bit of play in the monuments of up to 0.3. That does not worry me and I will return to look for more boundary points before I stake out the new garage. What I did find, which concerns me, is that when dissecting other surveyors’ plans the circles that appeared to be on the corner were not. I’ve seen this before in various ways. In this particular drawing the corner circles were graphically placed and, unless you used a CAD system, it would not be possible to see the difference. Generally, surveyors locally want to keep their precision guarantee to their paper prints at the printed scale and try to avoid responsibility for CAD accuracy.
When placing coordinate points on plans created by others, I have seen lines trimmed to the edge of the circle. Should you snap a coordinate to the end of the line, it will be off by the radius of the circle if the circle is at the actual corner. I have found pins on a property line 1 foot from the actual corner. I believe it was a case of snapping a point to what appeared as the end of the line. It’s always prudent to mistrust someone else’s drawing until you get a feel for their style. There is nothing wrong with trimming the line at the circle when the bearings and distances reflect good closures.
While researching a project at the recorder of deeds, I overheard title people talking about a local company and remarking that they always draft their plans upside down. I’m sure I looked like the RCA dog while processing the statement. They explained to me that north is always down for that company, whereas all the other companies had north generally up. I had seen many of those plans and they were dependable to be correct, but never did I realize they were upside down. The problem the title people experienced was in writing descriptions for the lots since they must be constantly aware of the direction of bearings. I have no idea why they draft them with south up, but the only reason I generally put north up is because it’s what somebody taught me to do.
Have you ever received a CAD plan to use for stakeout and the building is not square? I have, and it’s difficult to understand why. If I were to use the dimensions on a foundation plan and draft the building, it’s easier to make it square than off by small angles. Perhaps the engineer knew for their purpose they did not care about a tenth or minute of angle. So they may have closed the building and not realized it was good for scale but not for stakeout. That would be close enough for printing, but not for building. For this reason, we always request the most current version of the foundation plan on building stakeouts and we usually enter the foundation into the CAD drawing ourselves. In my opinion “close enough” for concrete is 0.01 feet. I believe if you try to be accurate all the time with proposed building corners, there won’t be any phone calls from contractors about inches out of square.
This also applies to steel work where bolts are going to be set. I recall a contractor talking about workers getting pretty angry when they have to start burning plates to get them over the bolts. I sure remembered his words. If your accuracy of 0.01 feet slips to 0.02 feet they can probably work with it.
Years ago, my employer had me survey a 300-acre tract. The traverse had a 1,000-foot error in closure. I was pretty upset telling him how terrible my work turned out. He responded, “That’s a good error. A foot would be bad error and hard to find. Let’s look at your plotting and search for a long line. Most likely it will be in one of your long traverse lines.” It took another person looking over my field notes to see that I was repeatedly incorrectly adding up my sub distances on a very long line running down the side of the turnpike, which was one line of the boundary. The closure was better than “close enough.” I was slope chaining a run of about 3,000 feet along the paved shoulder of the Northeast Extension of the Pennsylvania Turnpike.
Because this old farm was in a rural area, the deeds had poor closures and the tract was made up of many parcels. After our employer performed the boundary calculations, he wanted to join my crew in the field to see where the corners we set would fall so that he could see if they “looked good.”
The transit man turned the angle and our employer head chained to set a steel pin in what was basically a rock pile. I was carefully watching him to see how much effort he put into getting the pin into position. He banged, measured, banged more, measured more, on and on until “close enough!” was declared.
I commented, “Wow, that was a tough pin to set.”
He responded, “Yea, and you gave me that bent pin!”
Inside I laughed because I had purposely given him a pin that just happened to be bent because I wanted to see how hard he would try to set the pin precisely. He did a great job under the circumstances. That day was a learning day for me as to how close is “close enough.”