Conducting a Distance Azimuth Survey

Introduction

  Sometimes, technology fails; whether it be dead batteries or bad pixels on a GPS screen, technology is never 100 percent reliable. When this is the case, a distance azimuth survey can be conducted using basic non-technologically advanced tools. There are two different kinds of survey data: explicit and implicit. Explicit survey data is collected using a GPS unit or another geospatial device which will provide a point's exact geographic location. Implicit survey data is location data relative to a specific geographic location. A distance azimuth survey is a good example of using implicit survey data. This is because a distance azimuth survey is based off of a single reference point which all other survey points will be based on. The reference point is collected using a GPS unit, but all the other survey points can be collected using tools as simple as a compass and measuring tape.

Fig 7.0: Photo of the Study Area Where the Survey
was Conducted

  In this lab, a distance azimuth survey will be conducted in Putnam park which is about 100 meters south of Davies Center's front entrance on UW-Eau Claire's campus in Eau Claire, WI. This is a fairly wooded area which is located at the base of the hill which separates lower and upper campus. A photo of the survey area is shown on the right in figure 7.0.
   The survey will consist of measuring the distance and azimuth of random trees from the survey reference point. The diameter of each tree will also be measured. The survey will be broken up into three different sections each located in slightly different areas. Each area will have a survey of 10 trees which will correspond to a reference point. Also, in each area, a different combination of tools will be used to gather the distance and azimuth. However, the GPS and diameter tape will be used at each area to capture the geographic coordinates of the reference point, and to measure each tree diameter. An image of the GPS unit used is shown below in figure 7.1. In total, there will be three different reference points and
30 different trees surveyed.

Fig 7.1: GPS Unit Used to Capture Explicit Survey Data

Methods

Area 1

Fig 7.2: TruPulse Laser Used to Capture Azimuth and Distance 
Survey Data

  This area is located at the base of the stairs between McPhee and Davies Center. First, the GPS unit was used to find the coordinates of the reference point. Then, 10 random trees were chosen to be used in the survey. The azimuth and distance of these trees were then measured based off of the reference point using the TruPulse laser which is shown on the right in figure 7.2. The laser was pretty simple to use. When collecting the azimuth and distance data with the laser, one just needs to press the top button on the top to shoot the laser at the tree while making sure that the laser was on the correct setting. When doing this, it is important to make sure that there isn't anything in-between the laser and the tree so that an accurate reading is made. After this, the diameter of the trees were collected by using the diameter tape. After the data for the 10 trees were collected, they were then written down in a notebook to be used later.







Area 2

Fig 7.3: Using the Azimuth Compass
to Measure the Bearing

  This area is located about 100 meters southeast of area 1. The GPS unit was used again to record the reference point which would be used to base the survey on. Next, 10 more random trees were chosen to surveyed. Then, the unique tools were to collect the azimuth and distance for each tree. These unique tools included the azimuth compass which was used to measure the bearing (displayed in figure 7.3) and measuring tape which was used to measure the distance between the reference point and the trees. The azimuth compass was fairly difficult to use. One eye had to read the bearing on the compass while looking through a very small lens and the other eye had to be looking at the tree to make sure the bearing was on line. Lastly, the diameter tape was used to measure the tree diameters at chest height. Figure 7.4, below, shows Alex using the diameter tape. On the diameter measuring tape there was a metal hook which hooked into the tree and then the tape was wrapped around the tree and measured at the hook to see what the diameter was. After this data was collected for the 10 trees, it was written down in the same notebook as before.

Fig 7.4: Using Diameter Tape to
Measure Tree Diameter

Area 3
  Area 3 is located 100 meters southeast of area 2. Once again, the first step was to record the coordinates of the reference point using the GPS unit. The second step was to choose 10 random trees to survey out. Then, the Sonin sound wave device was used to measure the distance from the reference point to each selected tree. An image of our group using the Sonin device is shown below on the left in figure 7.5 and a closer image of just the Sonin device is shown below on the right in figure 7.6 . It took two people to use the Sonin device as there are two parts to it. One person had to stand at the reference point with one part while another had to stand at the tree with the other. Then, the person standing at the reference point would shoot the sound wave from their part of the Sonin device to the other Sonin device and the distance reading between the two Sonin devices would display on the screen. Then, the azimuths were measured using the azimuth compass tool just like in area 2, and the the tree's diameter was measured with the diameter tape. Then, this data was recorded in a notebook next to the other data.

Fig 7.6: Close up View Of the Sonin Device

Fig 7.5: Using the Sonin Sound Wave Device

Normalizing the Data in Excel

  Since all of the data collected for the survey was recorded in a notebook, the data had to be entered into excel. 24 entries out of the 30 can be seen below in figure 7.7. Each field was given a very standardized name such as X, Y, or Azimuth so that the data will be easier to add to ArcMap when making the maps. The Distance field is measured in meters, the azimuth field is measured in degrees, and the diameter field is measured in meters.

Fig 7.7: Excel Survey Standardized Data

Bringing the Data into ArcMap
  The Bearing Distance to Line tool was used to bring the the data into ArcMap. This tool asks for the reference coordinate values, the distance values, and azimuth bearings of the surveyed trees. From this, the tool will generate a series of azimuth lines which will represent the distance and bearing of each tree from the reference point.
  After that, the Feature Vertices to Points tool was used. This tool creates vertices at the end of line segments for a feature class. All that had to entered in was the line feature class just created above, and the new output point feature class. Doing this created points for each individual tree and for the reference points. Unfortunately, it created 10 points at each reference point because there were 10 line segments which had a vertex there. These extra points were deleted within an edit session because they were unnecessary. A new feature class was created and three points were added manually to display the reference points.
  After both of these tools were ran, there were both lines and points which represent the location of the trees, and the distance and azimuth of them.

Issues Encountered While in the Field
  The first issue encountered happened while using the TruPulse laser to measure the distance and azimuth in area 1. Sometimes it was difficult find the tree while looking through the lens because there was some brush in the way and the people measuring the diameter of the tree not standing by the right tree. This was overcome by having the person measuring the diameter of the tree go back the tree needing to be measured and then verifying that the measurement was taken with the person with the laser.
  Another issue happened when traveling from the different areas. Each area used a different set of tools to measure the distance and azimuth. However, the same tools were used to measure the coordinates, and tree diameter. Because there were three different groups, there was some confusion whether all the tools were to be left at the area when done surveying the trees in that spot. Some people thought that all the tools should be left at the area, and  some thought that only the tools that changed should be left at the area. This issue happened each time our group moved areas. This issue was never really solved, but was temporarily fixed when arriving at each area. Often, one person had to walk over to the previous area to either drop off some tools or pick some up.
  One other issue encountered happened while collecting data with the Sonin sound wave device. Because it took so short to record the distance and azimuth compared to measuring the tree diameter, the person measuring the tree diameter was consistently behind. For example, the azimuth and distance would be entered for trees one through five, but the diameter would only be through tree three. Eventually, this caused some error in the data because the wrong trees were being measured with the diameter tape and the trees surveyed with the Sonin and azimuth compass had been forgotten. This issue came about after all 10 trees had been surveyed. To fix this issue, a new set of 10 trees was picked out, and our group made sure to record everything very carefully and to not move from tree to tree so quickly.

Results

Maps

  Only one map was created for this lab as there was simply little enough data to fit all the attributes and features on a single map without making it too busy. This map can be seen below in figure 7.8. It is a proportional symbol map where the circles represent the location and diameter of the surveyed trees, the azimuth lines represent the bearing and distance to these trees based off of the reference point, and the yellow stars represent the survey reference points.
  Looking at the map, there isn't any clear spatial connection between tree diameter and anything else. This makes sense as the diameter was the only attribute collected about the tree. It wouldn't logical for the distance or azimuth to be related with tree diameter because they are arbitrary data to the tree and are based of a reference point. The largest tree diameter was 87 cm which is quite large while the smallest tree diameter measured was 18.4 centimeters. In general, the trees surveyed at areas 1 and 2 had a larger range in tree diameter than the trees in area 3 did.

Fig 7.8: Proportional Symbol Map Showing the Diameter, Location, Distance,

and Azimuth,  of the Surveyed Trees

Data Accuracy
  When first creating the map, the area 1 survey points didn't show up in the correct location. They showed up on the top of the hill near McPhee. This happened because the GPS unit was unable to get a good reading for the reference point. The large hill to the south and the densely wooded area made it difficult for the GPS to receive an accurate signal from satellites. To fix this issue, the actual location of where the reference point was supposed to be was determined by using the information tool and clicking on the correct location in ArcMap with a loaded base map. This gave a new set of coordinates which then had to be reentered into Excel and brought into ArcMap again using the same process as before. The points for areas 2 and 3 looked to be accurate, so those remained unchanged.
  There could have possibly been some data error when using the tools for gathering the distance, azimuth and diameter of the trees while in the field. The diameter of the trees were measured at chest height, but different people measured the diameter of the trees. This could have led to possibly some inconsistency in the measuring location for the diameter. Error could have also occurred if the wrong tree was measured when using the laser or azimuth compass. One error can be seen in area 1 where the one tree located just above the legend is placed. It is unlikely that this is actually the correct location of the tree because this is where the large hill is and our group didn't measure any trees on the hill. Fortunately, the rest of the tree locations look to be accurate.

Conclusion 

  A distance azimuth survey worked well for this lab, but in reality this method should only be used when other better ways of surveying isn't an option. A couple other ways include using a GPS unit to measure every survey point explicitly or creating and using a coordinate system if the study area is small enough such as done in the sandbox lab. The benefits of using an azimuth survey include that it can be performed relatively quickly, it doesn't require expensive tools, and that it is a good backup option when technology fails. Potentially, a distance azimuth survey could be used to map out things such as a golf course, tree type, or even property boundary if the surveyor was careful enough.