A weekend of ups and downs

Starting before dawn on Saturday morning, and ending after dark on Sunday evening, I was away from home at our Raccoon Creek Community site with our surveyor and his assistant surveying most of our property. The two of us who carried the "sticks" probably each walked about 10 miles, up and down, up and down, ...

The finished product of the survey will be a topographic map of the site with 1-foot contours. Currently, the best topo we have is the USGS 10-foot contours. That only gives a rough idea of the site, not enough detail to plan any building locations, roads or ponds and water catchment locations.

We did not survey the entire site, partly because there is a "tail" section that we aren't likely to "develop" to the extent that a 1-foot topo is needed, and partly because we wanted to take all the "shots" within two days.

The process was very instructive. Modern surveying equipment makes the job way different from when I played surveyor as a kid with a scope and a friend with a marked stick. The primary piece of equipment, the transit or theodolite, is a complex box about the size of a few bricks. It calculates direction, angle of elevation above or below, and, using infrared beams, the distance to the "stick" to within thousandths of a foot.

The "stick" is an extendable pole with a point on the top and bottom with a very precise circular mirror at a fixed height. Markings on the inside pole tell one how far from the ground the point is. These mirrors are remarkable. They are actually made of six mirrors that each are precisely 60 degrees of the circle. These are precisely set in a concave six-sided pyramid so that no matter from which direction one looks into the assembly, one sees the same picture of oneself. Move up or down, left or right, and one still sees the same part of one's face. This is very important, of course, because the mirror needs to precisely bounce the infrared beams back to the transit, and the stick holders cannot possibly get a precise 90 degree angle on the transit from sometimes hundreds of feet away.

So the process is to set up the transit on a point and take "shots" of the sticks at various points within sight of the transit. Each of these sightings are stored in a computer as data points. When all the points that can be shot from the transit are taken, the transit is moved to another point. A stick is placed where the transit was, and a shot is taken from the new point back to the previous point to verify their relationship to one another.

This process continues across the entire site, setting transit points by "backshooting" to earlier ones, and taking shots in every direction from each transit point. The more shots, the more precise the end product will be.

The trick is to take enough shots to get all the contour changes so the computer, where all the data points are processed, can place the data points on the map and interpolate between them to describe the contour lines. To get the best detail one must take shots on the center line, the "center of flow", of each stream, and the "toe" and "top of bank" on both sides. These five shots are taken at points along each stream where the route or the elevation changes. Shots are taken where there are changes in the slope, and also at scattered points across the entire area.

Again, the more shots, the better the product, but, obviously, there's a point beyond which the cost would outweigh the value of the extra precision. With two days to take the data points, we had to decide where to spend more time to get more shots and more detail, and where more detail wouldn't be all that useful, and, consequently, we could take fewer shots and still get what we need.

Within a week we should see the result of our work.