Digital Elevation Survey I & II

Digital Elevation Survey I

Introduction

The purpose of this assignment was to create a surface terrain and survey this area without standard survey techniques.  In order to do so, we had to come up with a suitable coordinate system and survey technique that would account for our study area.  Geospatial and critical thinking were essential because only a tape measure, rope and a meter stick were available to conduct the survey.  Unfortunately, migraines don’t take class assignments into consideration and I wasn't able to attend the actual survey.

Methods

Because I was sick and unable to attend the survey, so I am using the data of my group members Phil and Tonya.  The first step in this assignment was to construct the terrain (Figures 1 and 2).  Our terrain included a ridge, hill depression, valley and plain.  This was done by hand in our study area which was planter box in the courtyard of Phillips.

Figure 2- Creating the terrain

Figure 1- Creating the terrain

The next step was to set up the coordinate system for the survey.  Before the physical collection of the survey, we had discussed what the best coordinate system would be.  We decided that the short end of the planter box became the X Axis and the long edge became the Y Axis.  When it came time to collect the X and Y measurements, my group members decided it would be best to use a mobile X Axis for accuracy.  A meter stick was taped to a larger stick for the mobile X axis.  Because the mobile X axis would be gliding on the outer wooden edges of the planter box, all elevations had to be lower than this height.  Phil and Tonya had to “shave” down some of the previously formed ridges and hills.  The Y axis also had a tape measure taped to the edge of the planter box.  This helped not only for an accurate Y measurement, but also an X measurement because the mobile X axis could be measured with the Y Axis so it was completely straight.  The origin of our coordinate system was very traditional at 0,0.

X and Y measurements were taken at 5 centimeter intervals where the surface had in increased amount of terrain features and 10 centimeter intervals where the surface was smoother.  As seen in image 3, once the measurements were taken for the length of the X axis, the mobile axis was shifted up to the Y axis.  The Z measurements were taken with a meter stick vertically placed along the terrain (Figure 4).  This was done for the entire study area.  The measurements were recorded onto an Excel spreadsheet.

Figure 3- Collecting X, Y and Z coordinates

Figure 4- Collecting X, Y and Z coordinates

Figure 4- Excel Spreadsheet

After the survey was conducted, the measurements were digitally imported into the Excel spreadsheet (Figure 4).  All Z measurements were in negative numbers, so 17 was added to each measurement.  The number 17 was added because the lowest Z measurement was -16.  This ensured all measurements were a positive number which allows for easier calculations.

Discussion

I am really disappointed that I was not able to help with the physical collection of our data.  Being absent from the most important part of an activity really shows how important this aspect of the assignment is.  My group members would not have struggled as much if I would have been there because it is a hands-on activity and as they say, “more hands make for lighter work.”  Also, it is hard to comprehend the data because I was not present in the collection.  This can be thought of in ways outside of just this assignment.  Data interpretation is essential in geography because it can manipulate the meaning of the data if it is misinterpreted.  It is essential in this activity to be present to really comprehend the importance of Geospatial thinking.  Without being physically present in the data collection, I missed out on the problems and wasn't able to suggest ideas to overcome these problems with the survey.

Conclusion

The biggest thing I have taken away from this assignment is the great necessity of being physically present in data collection of our study or survey.  Without being present, you can miss important aspects to the data and you are not able to solve problems with group members.  I look forward to revisiting our study area and hopefully the weather will cooperate so our surface terrain is similar to the state we left it.

Digital Elevation Survey II

Introduction

This week, we revisited our "Digital Elevation Survey" activity.  The goal was to refine our survey area and tweak our methods for the best representation of our terrain.  Before we could refine our data, we imported our X and Y coordinates into ArcMap.  In ArcMap we used the IDW, Kriging, Natural Neighbor and Spline Raster Interpolation tools to visualize the terrain.  We also used ArcScene as a 3D interpretation.  Below is an image of the Spline technique in ArcScene (Figure 1).  This method was the best representation of our terrain.  The spline tool uses a 2D "minimum curvature technique" to interpolate the raster surface.  This tool differs from the other because the resulting surface passes through the input points exactly and creates a smoothing effect.

Figure 1-Spline Interpolation of the first digital elevation survey

Methods

Once we had visualized our survey, we came together as a group to discuss ways to better our research.  We decided to tie string at 10 mm intervals on the Y axis so our coordinates would be more precise (Figure 4).  The next step was to replicate the activity from the previous week.  Because it had snowed, we had to recreate our terrain (Figure 2).  After the terrain was recreated, we tied the string at 10 mm intervals on the Y axis (Figure 2 and 3).

Figure 2-Creating the terrain

Figure 3-Tying string at 10 mm intervals

Figure 4- 10 mm intervals on the Y Axis

  

After the string was tied, we began to collect our survey data in the same process as before.  For most of the survey, we took X, Y and Z coordinates at 5 mm intervals.  This would give us more data points and therefore a more precise digital elevation survey.  Like the previous time, we used a mobile X axis (Figure 5) to measure from X, but because we had string tied at every 10 mm on the Y axis, the measurements were more precise.  In areas where the terrain was flat, we took measurements every 10 mm (Figure 7).  We used a Microsoft Excel spreadsheet to record the data points.

Figure 5- Mobile X Axis

Figure 6-Laurel and Phil collecting data points

Figure 7- Meter stick with mobile X Axis to collect data

Once the entire planter box (112.5 cm by 224 cm) was surveyed, we converted the Excel spreadsheet into a digital copy.  We then imported this spreadsheet into ArcMap.  Again, we used IDW, Kriging, Natural Neighbors and Spline Raster Interpolation tools to visualize our data.  In the first attempt at this activity Spline Interpolation resulted in the best terrain model, this technique produced the best visual as well in the second attempt (Figure 8).

Figure 8- Spline Interpolation for the second survey

The second time we conducted the survey elevation features were more pronounced.  This was most likely because we took more data points and the data points were more precise.  The features were not vague representations the second time, they were replicated extremely similar to the real world features in our planter box.

Discussion
By revisiting our activity, we were able to use our previous data and outcomes to produce a better product the second time around.  We made two major changes between the first survey and the second.  We collected more data points and used string to collect more precise Y locations.  There is an obvious difference between the first Spline interpolation visual and the second.  The changes we made allowed for a more detailed representation of our digital elevation survey.  To make our survey even better, we could have used a measurement tool other than a meter stick.  A meter stick is rather wide, so our measurements would only account for the general elevation of a point.  If we used a thinner tool, the data points would be represented more accurately.  We were somewhat restrained from using this tool because we were instructed to use a meter stick.  Also, I didn't think of this until we were about halfway done collected the data for the second survey.

Conclusion
This activity really advanced my ability in the Geographic realm.  It is easy to sit at a computer and import XY coordinates and project them into a visual display, but it is harder to come up with your own data collection technique and import that into ArcMap to produce a visualization of our survey data.  This activity pushed me to think more critically about data collection and the importance it has on the desired outcome.  My group performed very well together.  We were able to account for each other's weaknesses and use our strengths to come up with the best possible survey.