Assignment #4: Distance Azimuth Survey

Introduction

For this exercise, we were to learn how to do surveying without a GPS.  We were to use a rangefinder to measure slope distance and azimuth and then record points to create our survey.  The Azimuth compass starts at 0 degrees as true north, and then going in a clockwise rotation, 90 degrees is found to be east, 180 degrees as south, and 270 degrees as west.  Slope Distance is more accurate than straight distance when measuring distances along the Earth’s surface as it takes into account the curvature of the Earth in its measurement.  If you know the coordinates of one starting point and are able to take several slope distance and azimuth readings of other stationary objects visible from the starting point, you can accurately map where they are.

Methods

We used a TruPulse 360 Laser Rangefinder.  This device allows you to take a reading of a stationary object and immediately get its slope distance and azimuth from the starting location.

The TruPulse 360 Laser Rangefinder

We proceeded outside to the location of our first starting point, in front of the railing in the center of the stairs in front of the Schofield Administration building.  We took twenty-five readings from this point.  To take a reading, the instrument was held up to the eye and directed at a stationary target.  The crosshairs of the instrument we held in place on the object while the button on top of the device was held down for a couple of seconds.  This captured the distance to the object and displayed it as a digital display on the viewing window of the device.  Next, by pushing a button on the side of the device (the down arrow), twice, the device was switched from taking the distance reading to taking the azimuth reading.  We did this work as a group, so we rotated between one person using the instrument and taking a measurement, another person recording the information in a notebook, and the third person helping the instrument-user keep track of the objects being recorded. 

Zach using the TruPulse at our starting location

We took twenty-five readings at the first location and then moved on.  Owing to the thick layer of snow on the ground, we were forced to take readings of items with enough height to be visible.  The majority of the readings we took were off of trees.  We were able to capture readings from park benches, heating vents, road signs, and light poles as well.  We walked across the way and stood at our second point, at the edge of a railing near the UWEC campus footbridge.  From this position, we took an additional twenty-five readings.  When this was done with, we moved along a path in front of the walking bridge and took our remaining twenty five readings. 

The view from our third location

Once these were collected we returned and copied the readings from our notebook into Excel.  If we had used a laptop or tablet device in the field to record our readings and had been able to directly record them into Excel we could have been able to skip this step.  Anyway, we got our Excel spreadsheet set up.  The next step was to import the Excel spreadsheet into Arc Map.  First we set up a geodatabase.  This was done by going into Arc Map, opening up the Catalog tab (typically found along the right side of the interface) and navigating to the folder where we want to save our work.  Then, by right-clicking on the folder, we choose “Create new file geodatabase.”  This opens the Table to Table dialog box (figure).  For Input Rows, use the folder to find the spreadsheet and select the sheet where the data is kept.  Output Location is already filled in, and the only other thing to do is to provide a name for the imported table in the Output Table box.  Click OK and the table is imported.

Next we need to create a feature to display the numbers visually in Arc Map.  We will use two Tools from the Arc Toolbox: Bearing Distance To Line and Feature Vertices To Points.  Bearing Distance To Line is found in Arc Toolbox under Data Management Tools, Features, Bearing Distance To Line. 

The Bearing Distance To Line Tool and its location in the Arc Toolbox

To use this tool, specify the imported spreadsheet for Input Table by using the dropdown arrow and matching the fields up from the spreadsheet for each of the four boxes likewise.  The Azimuth column goes in the Bearing Field box.  Click OK and the feature is created.

The created feature after running the Bearing Distance To Line Tool

Since what we want to show are the ends of these lines on the map, as they are the objects that we took our readings off of in the field, we need to use the Feature Vertices To Points Tool.  This Tool is found in the same folder in Arc Toolbox as Bearing Distance To Line. 

The Feature Vertices To Points Tool and its location in Arc Toolbox

For Feature Vertices To Points, simply choose the feature created in the previous step for the Input Features box with the dropdown arrow and click OK.  Points are now created at the ends of all the lines.

The Point features created after running the Tool

Finally, our basemap of satellite imagery is added to Arc Map.  The colors of the lines and points can now be changed to stand out better against the basemap.

The finished survey



Discussion and Results

The survey turned out all right, although there were a few problems with it.  First of all, there are some points that are way off, appearing to be in the center of buildings or in the water.  These points could have resulted from not having the rangefinder totally steady when taking measurments.  If we had used a tripod to steady the rangefinder we could have greatly improved the accuracy.  Second, the starting locations on our map appear just slightly off from where they should be, by a matter of a couple of feet.  This is not horrible, but could also have been more accurate.  All in all, this was a good exercise.  We learned how to create a survey of an area without the use of GPS.  If GPS is not available, this method would be very valuable.