Introduction
The distance azimuth survey technique is useful in trying to determine and pin-point the exact locations of certain features. This method can be applied to many fields and has numerous applications. The distance azimuth calculates the distance between two points and the angle from true north. This is helpful when you want to return to a specific location, a coordinate point may not be accurate enough.
The objective of this activity was to select a study site and feature to survey and obtain the distance and azimuth of each feature. Then it was required to import the data into ArcMap and display the study site with the distance azimuth lines and points to see how accurate we could be.
Study Area
Date: 1 October 2015, 11am-12pm
Location: Owen Park, Eau Claire, Wisconsin
Conditions: Sunny, Average temp. 65°F (retrieved from Weather Underground)
Methods
Materials
TruPlus 200 Rangefinder
GPS Tour App
Data Table
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| Figure 1. TruPlus 200 Rangefinder. |
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| Figure 2. GPS Tour app. |
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| Figure 3. Set up for the data table used in this activity. |
Collecting the Data
We selected a location in Owen Park where we could easily view one hundred trees. We chose trees as our feature because there are many in Owen Park and we knew we would be able to reach one hundred data points.
First, we took our GPS location by using the GPS Tour App. According to the app we were at E-91.500481 and N44.803508.
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| Figure 4. Study area Owen Park, Eau Claire, WI. |
When using the TruPlus 200, we kept all electronics and metal objects far away from the device in order to not skew where true north was.
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| Figure 5. Alyssa Krantz taking points with the TruPlus 200. |
Trees were chosen as the attribute information field type because we wanted to record one thing that was abundant in the Owen Park area. The 100 trees surveyed for this activity were the trees that could be seen from the point of origin.
Importing the Data into ArcMap
Create a new file geodatabase
Set this geodatabase as the default geodatabase by going into the Page and Printer Set Up from the File tab
Right-click on the geodatabase and select Import Table (single)
In the Table to Table menu:
Select the Table and sheet containing the data
Review that the Output table is set to the default geodatabase you created
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| Figure 6. Within the ArcToolbox Data Managment Tools, Bearing Distance to Line and Feature Vertices to Points was used to create the map. |
In the Bearing Distance to Line interface select the sheet from the imported data table
The output feature class should again be set to the default geodatabase.
The X-field refers to the longitude of the where the data was taken and the Y-field refers to the latitude. The distance field is as it implies the distance measurements of the data (taken from the laser) and the Bearing Field is the azimuth the laser calculated.
After clicking ok, ArcMap will draw lines from the point of origin (latitude and longitude) to each of the data points. To clearly see where the feature lies on the map it is necessary to use a different tool from ArcToolbox.
In ArcToolbox select Data Management Tools and Features again. This time choose the Feature Vertices to Points.
Within the Feature Vertices to Points window set the input feature to the sheet of the imported data table and the output feature class should be set to the default geodatabase.
As for point type, this should be set to END because for the distance azimuth activity it is only desired to show the end of the line, where the feature is.
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| Figure 7. Distance azimuth of trees in a section of Owen Park, Eau Claire, WI. Map made using ArcMap. |
Metadata
Who: Morgan Freeburg and Alyssa Krantz
What: Collecting Data using Distance Azimuth
Where: Owen Park, Eau Claire, Wisconsin
When: 1 October 2915
Why: To collect data by distance azimuth
Discussion
The results from our survey were somewhat accurate. On the map it appears some of the trees appear to be on the sidewalk or edge of the road. Obviously, this was not the case. The error could lie in the lack of precision of the GPS device used to record our point of origin. Another source of error could have been the perception of the trees through the laser distance finder. Alyssa mentioned it was difficult to see some of the farther trees and get a steady reading from the device. This could be because a tree may have overlapped another somewhat blocking the view of another behind it or the fact that it was too far away in the first place. On the other hand maybe if we selected a different basemap with more detail, the points would lie more accurately on the map.
Some problems we encountered specifically using ArcMap was the data table was incorrect and only displayed half of our points. Originally, a handmade table was used and then the data was entered into an excel spreadsheet. If the data had been originally entered into an excel these problems could have been easily avoided and personally saved me two hours of time trying to fix the errors. There were only two values entered incorrectly, but ArcMap would not import the table for unknown reasons. Finally, with a BRAND new data table, ArcMap allowed the importation.
Another item that we would change for the future is how to obtain the point of origin. As said above we used a GPS point. Our origin would not be easily identifiable from a google earth image or bing image because of the tree cover and an arbitrary start point. It would have been better to place our origin at the corner of a street or near a landmark of some sort. The downfall for our specific experiement to that alternative would have been would couldn't have seen as many trees.
The laser distance finder was a great tool to use in order to analyze the distance and azimuth of the features, which can be applied to just about anything. It streamlines the process of using a compass and measuring tape taking hours and hours to get a handful of points. To obtain the distance azimuth data for 100 trees it took only one hour. This method of obtaining data is very efficient. On the other hand, some disadvantages we ran into was if a certain feature was blocking another feature behind it. That would prove important if an individual needed to record the location of a feature away from a certain point. The feature would be missed altogether. Also, this method heavily relies on the accuracy of how you obtain your point of origin. By using a GPS the location could be somewhat unreliable, or if a map was used to pin-point the location to the origin a specific map of the study area would be needed.
Conclusion
In conclusion, this method of surveying a large area in a short amount of time was very effective. There were some inconsistencies of points being in the incorrect places, however this could have been due to the fact of the GPS app, human error of moving while taking the measurements, etc. Otherwise, displaying the data in ArcMap went smoothly after the data table was corrected. It seems that conducting a distance azimuth survey is very user friendly (with the equipment we used), effective, and efficient.
References
http://www.forestry-suppliers.com/product_pages/Products.asp?mi=38721
https://itunes.apple.com/eg/app/gps-tour/id492684276?mt=8
http://www.mc.edu/rotc/files/6413/1471/7292/MSL_201_L03b_Land_Navigation.pdf
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