Distance Azimuth Survey

Introduction

Figure 1. Measuring diameter of a tree
using a standard tape measure

The purpose of this lab was to explore different ways of surveying for when certain technology, such as a GPS device, may fail or be unavailable. Three different sites were surveyed, each using a different method. Each method involved measuring the diameter of the trees with a measuring tape (Fig. 1) and the latitude and longitude were measured from each focal point for spatial reference (Fig. 2). One method used a TruPulse laser that calculated the distance in meters as well as the azimuth in decimal degrees (Fig. 3). A second method used a regular compass for the azimuth and measuring tape for distance (Fig. 4 & 5). The third method required a device called "Sonin Combo Pro" (or rangefinder) (Fig. ) which sent a signal from the device at the focal point to a person holding another device next to the tree in order to measure the distance, and a compass. This data was considered to be implicit, which means it is all relative or approximate. Explicit data is exactly tied down to a geographic point.

Figure 2. GPS used to find longitude and
latitude at each focal point.

Figure 3. TruPulse laser device used to measure
distance and azimuth in the field

Figure 4. Normal compass for finding azimuth.

Figure 5. Excitedly using a measuring tape to measure distance

Methods
Study Area

Figure 6. Study Area in Putnam Park.

The three sites from which data points were collected were all located within Putnam Park on the UW-Eau Claire campus in Eau Claire, Wisconsin. Each location had snow cover as well as a number of red/white oaks of diameters ranging from 18cm to 86cm. The three sites were chosen to be spread apart from each other, but other than that, there were no criteria for site selection. Each focal point was chosen to be in the center of the woods rather than on the edge near the street so that the lasers could accurately reach the trees being measured (Fig. 6).

Data collection
Points were handwritten as they were measured in the field and later entered into an Excel spreadsheet and normalized (Fig. 7). The latitude and longitude where measured at the focal point of each study sight using a GPS device. The distance (from focal point to tree) was measured in meters, azimuth was measured in decimal degrees, and diameter of each tree was measured in centimeters.

Figure 7. Sample of data in Excel spreadsheet after normalization

Map Creation

Figure 8. Results after using
"Bearing Distance to Line command"

Figure 9. Results after using "Feature
Vertices to Points command"

Before the data could be brought into ArcMap, it needed to be normalized. This was done by taking the latitude and longitude values and dividing the minutes by 60. The data table was then brought into ArcMap using a tool called "Bearing Distance to Line Command" which is found in the toolbox under Data Management and the Features. This created a series of lines outward from the focal point (Fig. 8). Next, a tool called "Feature Vertices to Points Command" was used to turn each of the trees into points on the map (Fig. 9). This tool is found under the same category as the first tool, and what it does is it creates a feature class points from vertices of the input features. After this, basic mapmaking techniques were used to create a study area map (Fig. 10) and individual maps of each study site (Fig. 11).

Figure 10. Final map of study area including all three sites with tree locations at appropriate azimuths and distances.

Figure 11. Individual study sites using three different survey methods. Site 1: TruPulse device. Site 2: Compass and measuring tape. Site 3: Sonin Combo Pro device.

Results/Conclusions
This lab provided three new techniques for surveying which do not rely on heavy technology. This is very useful for varying conditions as the outdoors can be very unpredictable in terms of weather. It is also helpful because sometimes time or money restrictions do not allow for expensive gear or repairing broken gear. It is very important to have a back-up plan when doing field surveying so that the job can still be done under any circumstances. Each of these methods seemed reliable enough, however the basic measuring of each element with an old school device such as compass and measuring tape always seems to be the most reliable technique because there is no allowance for technological glitch. It seems that drone surveying has replaced this type of surveying because it is just so much faster and easier and can include tons of data in just one field survey.