Thirty-six years ago, when I first entered the land surveying profession, the typical survey crew consisted of 3 persons:
- The Party Chief
- The Instrument Operator
- The Rod Person
Much of the technology that we enjoy today had not been invented yet. For instance, our total station had a built-in Electronic Distance Measurer (EDM). We all thought this was pretty slick, because we no longer had to drag around a 200 feet long steel tape. Using a tape meant we had to stretch it to the proper tension, correct for sag, correct for temperature, make sure we kept it level, and each end of the tape had to be suspended over a precise spot by dangling a plumb-bob from the ends of the tape. Compare this to using an EDM, where all we had to do was stick the rod with a prism on top over the point being measured to, and “Beep … beep … beep … BEEEEEEEP” the EDM would display the distance between the total station and the prism.
Data collection had not been invented yet. This meant that we had to record each shot in a field book with a pencil… God help the person who lost their pencil and didn’t pack a spare! What else had not come to pass was the capability of the total station to electronically display the measured horizontal and vertical angles. So the instrument operator, after carefully sighting the cross-hairs on the target in the scope, had to look into the second eye-piece which displayed a micrometer. There he/she would first dial in the precise degrees, minutes and seconds of the horizontal angle (relative to the backsight) and read it out loud to the party chief, who would write it in the field book. The instrument operator and party chief would then repeat this for the zenith angle (relative to straight up). Therefore, each shot had five (5) components:
- Point number
- Description of the shot
- Horizontal angle
- Zenith angle
- Slope Distance
We also had to keep a record of the Height of the Instrument (HI) and Height of the Rod (HR) with each shot. Can you see the potential for human error in any of these steps?
Notice I said the distance given was a “slope distance”. This meant we had to later “reduce the notes”. This involved several calculations for each shot.
Horizontal Distance = sin(zenith angle) * slope distance
Vertical Distance = cos(zenith angle) * slope distance
Shot Elev. = Ht.of traverse point + HI + vertical distance – HR
If you’re feeling adventurous, go ahead and see if you can determine the horizontal distance, vertical distance and elevation of point #536 above.
Most topographic shots were plotted on a large sheet of paper using a protractor (plotting the horizontal angle from the backsight) and a scale (plotting the horizontal distance).
Shots that needed more precision, such as monuments, iron pins and traverse points, were determined to 4 decimal places. This was done by calculating the change in Northing (latitude) and change in Easting (departure) from the traverse point. I won’t bog you down with those equations.
On an exceptionally good day, a field crew could shoot & record up to 250 points!!! If you really want to be tortured, ask me about how we did construction stake-out.
Fast forward to the year 2023.
I am fortunate enough to work at Howell Surveying, where there is a policy to invest in the latest & greatest technology. We have robotic total stations that follow the rod & transmit, via blue-tooth, the measurements to the data collector hundreds of feet away. The data collector then calculates the northing, easting and elevation of the point, stores it, and plots it on the hand-held display. The 3-person crew has now been reduced to a 1-person crew.
We have drones equipped with GPS and LIDAR that can fly over a 20-acre site and create thousands of ground points in a matter of minutes. Computer software plots these points, generates linework and surfaces, and enables surveyors to produce plans of exceptional quality.
My, how times have changed !!!
Answers:
- Horizontal Distance=31.83’
- Vertical Distance=11.36’
- Elevation of Point 536=485.09
