ON-SITE MEASUREMENT SYSTEMS

Regardless of the need or amount of on-site measuring required, it is a task that is best accomplished by the designer and an assistant using a metal or cloth tape measure, preferably 100 feet long. Two people can more accurately locate both ends of the tape measure and pull it taut to ensure correct measurements. When only one person can do the measuring, a long-necked screwdriver, stake, or similar item can be used to secure one end of the tape by inserting it through the hook at the end of the tape and pushing it into the ground (Figure 6—16). Although this is not always the case, it is usually best not to permit the homeowner to do the site measuring because of the lack of experience and appreciation for precise measurements. If the homeowner does the site measuring, the designer should double-check key measurements to verify their accuracy.

There are three techniques for measuring distances on a site: (1) direct meas­uring, (2) baseline measuring, and (3) triangulation. One needs to be acquainted with all these techniques because each serves a different purpose in locating existing site elements.

Direct Measuring Direct measurement is the most common method for taking measurements and is used between edges that are parallel to each other. The tape measure is simply stretched perpendicularly between the two edges, and the meas­urement is read. Figure 6—17 illustrates the use of direct measurement to locate (1) the edge of a sidewalk from the edge of a brick wall, (2) the edge of a concrete ter­race from the face of the house, and (3) the edge of the sidewalk from the face of the house.

Baseline Measuring Baseline measuring is used to locate a series of points or ele­ments that are on or very near a straight line or “baseline” such as a property line, fence, walk, or house wall. The tape measure is stretched along the line and meas­urements are taken where key points and edges are located. The top half of Figure 6—18 shows the tape measure stretched from the face of a house to the nearby property line. The fence is located 23 feet from the house and extends to a distance of 63 feet from the house. The tree is located at 79.5 feet from the house and the prop­erty line is 93.5 feet from the house.

It is recommended that the end of the tape measure be fixed in one location and that all the measurements along the baseline be taken in relation to this single beginning point. As can be seen, four separate measurements could have been taken in the

preceding example (bottom of Figure 6—18). However, moving the tape measure con­sumes time and increases the possibility of misreading the tape measure.

The baseline method of measuring is strongly suggested when measuring the lo­cation of doors and windows of the house. Figure 6—19 illustrates the tape measure stretched along the side of the house. Each door and window jamb (side) is located a specific distance from one end of the house where the front end of the tape measure is

placed. A separate baseline is used for each side or wall of the house. Another example of baseline measuring is to locate where the edges of the driveway cross the property line (Figure 6-20).

Triangulation The triangulation method of measuring is used to locate a point in relation to two other known points. For instance, assume there is a tree on a site that needs to be accurately located (Figure 6-21). To do so, two nearby corners of the house are used (Point A and Point E) as reference points. Simply measure and record the distance from each house corner to the center of the tree. Later when preparing the base map, each of the same corners of the house serves as the center of a circle with the radius being the distance measured to the tree. When the circles are drawn on the base map, they will intersect at the center point of the tree. This method of locating specific points is useful in locating other individual elements such as poles, lights, and utility boxes.

Triangulation is also a good method to use when lines or elements are not paral­lel to each other. Figure 6-22 shows a row of trees that are not parallel to the house. To locate these trees, both the southernmost tree and the northernmost tree are first independently measured using the triangulation method. Then the other five trees are found using the baseline method by stretching the tape measure from the southern­most tree to the northernmost tree.