Low-tech Distance Azimuth Survey Practice

Introduction

Sometimes technology fails. For times when GPS and other technology has failed or cannot be used, low-tech options need to be understood for supplemental implementation. One of these low-tech options is distance azimuth surveying. In its most basic definition this is the collection of a single coordinate point, a distance, an azimuth (bearing), and data about the object being located.

We practiced this method on Putnam Drive, behind the Phillips science building and the Davies student center on the UW - Eau Claire campus. We measured distance of ten trees from each of three points, each point's GPS coordinates, the azimuth of the tree from the point, and each tree's circumference. Though GPS coordinates may not be available for collection of the initial point in situations requiring this type of survey, a landmark could be picked to measure distance and bearings from, and this could be pinpointed later in georeferenced or orthorectified aerial imagery to find the coordinates.

Methods:

Like stated before we went as a class to Putnam Drive to survey in three groups of about 6 each. Trading jobs periodically each member of each group did every job for practice. At one of the three points being surveyed from a compass (of the type that is looked through with one eye to see the azimuth while the other eye is fixated on the appropriate point) and a tape measure were used. At another area, a compass and a distance measurement device with two pieces (one with the measurement reading and one that the other unit used to get its measurement) were used. At a third point being surveyed from a laser gun was used that gave both distance and azimuth readings. At all points being surveyed from a small tape measure was used for measurement of the circumference of each tree. This was measured in centimeters, while the distance to the tree was measured in meters and the azimuth was measured in degrees.

After collecting this data in the field on paper the table was brought into Microsoft Excel. The table created for this project is shown in Figure 1. One important detail with the creation of this table is that capitals and spaces should not be used for the column titles. ESRI software will choke on processing the data later if these are used. Also note that the GPS coordinates observed from the three unique survey points are stored in the x and y fields.

Figure 1

After creation of this table the data could be brought into a new ArcMap map. The table contained within the excel file was brought into the table of contents. In ArcMap a new file geodatabase was created and named the default geodatabase for the map file. This can be seen in Figure 2.

Figure 2

The data was now converted into lines by using the Bearing Distance to Line tool. This was run with the parameters as seen below in Figure 3. All tools used in this project were found using the search function in ArcMap. This function can be seen alongside the tool in Figure 4.

Figure 3

Points were then created from the lines that were created in this last step by using the Feature Vertices to Points tool seen in Figure 4.

Figure 4

After creating these lines the final maps displaying the data were made which can be seen below under results in Figure 5. These were created in ArcMap by using a data frame for each map and adding the layers needed for each in each separate data frame (added by selecting the Insert menu, then Data Frame). Base maps were added by using the Add Data button  down arrow, then Add Basemap, finally selecting the topographic map in the resulting window. Text was added via the draw toolbar, and north arrows, scale bars, titles were added using the Insert menu.

Results:

The resulting maps created are shown below in Figure 5. Clearly seen in the top locator map are the three separate points surveys were conducted from. Below that map are the three separate areas surveyed in at a greater scale.

Figure 5

In reflection on the accuracy of the data, there are a few concerns. First is that after adding the basemap it was apparent that the initial GPS coordinates which marked the points from which the other points were taken (using distance and azimuth) were not accurate. These errors could either be attributed to poor GPS data or inaccurate basemaps, but it is far more likely that the error was caused by the GPS data accuracy. This is speculated because basemaps were created by ESRI, of whom the highest accuracy is expected, and because the data was collected at the base of a steep hill and under dense tree cover, where low GPS accuracy could be a possible issue. Also, the inaccuracy of the GPS coordinates made the points move to both sides of the road on which point one and two were collected from, and if the issue was bad digitization by ESRI the points would likely have only been on one side of Putnam Drive indicating a slight north-south inaccuracy in digitization. A different reason this GPS data could be wrong is that the coordinates were recorded by hand from the GPS unit, and the GPS unit may have simply not updated fast enough to the new location or a user could have written down a wrong digit. This GPS error would not be a problem however if a marked landmark or something else was used instead, possibly one seen from aerial imagery whose coordinates could be found later. In a situation in which you would not have a GPS unit, you would have no GPS coordinates!

Another concern is simple user error in reading the compass bearing. The compass with which one looks through and uses double vision to read is especially concerning. It is slightly difficult to get the correct reading. Instructions worth reading before attempting to use one of these compasses can be found here. This was not a problem however when using the laser distance measuring instrument which displayed a bearing at the same time as the distance to the object being pointed to with a click of a button.

Conclusion:

In a pinch, a distance azimuth survey works! In situations in which GPS technology is not available or cannot be used, and especially if practice has been had with the equipment that would be available,   moderately accurate data can be collected.