Creating a Digital Elevation Surface

Introduction

A general map of the University of Wisconsin-Eau Claire campus.  The red
star shows approximately where our plant box is.  (Google Maps, 2014)

     This exercise provided a great way to break into geospatial thinking.  While other classes have cookie cutter directions that a monkey could do, this class requires critical thinking to create our own steps to figure out problems.  Each group in this first assignment was allocated one flower box in the courtyard of Phillips Science Hall with dimensions of about 235 cm long by 110 cm wide to create a terrain.  The requirements were to have a hill, valley, ridge, plain, and a depression in our terrain somewhere within our given space.  It did not matter where they were in the box or in relation to one another and it did not matter how large or small they were.  The groups were required to determine a sea level point (zero elevation) in our designated area.  Next, the groups needed to come up with some sort of coordinate system for the designated area.  The coordinate system is arbitrary and does not need to correspond to true north in the real world.

Google Earth imagery of Phillips Science Hall.  The red star shows approximately where our plant box is.

I was part of group three along with Zachary Howard, Jeremy Huhnstock, Blake Johnson, and Cody Kroening and we built our terrain and conducting our surveying of that terrain on January 29, 2014.

Methods

Jeremy and Cody building a
mountain.

     An infinite number of paths could have been chosen for how to complete this project.  Our group decided to have the top edge of the plant box to be our sea level (elevation of zero). One of the first things we noticed in our plant box was a large chunk of soil protruding upwards towards one of the ends of our plant box.  We decided that we would put our ridge there, so we would not have to worry about digging out this frozen soil.  Other than that spot, we smoothed over our terrain with a large wooden board, which allowed all of our building to start at our zero elevation level.  In hopes to make our three-dimensional digital models of the terrain to really stand out, we wanted to create a dramatic landscape.  To fulfill this goal, we built above the line that marked the edge of the flower bed, and we dug into the snow that filled it up.  We wanted to make our terrain unique, so we made a three step terrace, making the deepest one down to the soil, without having to dig any out.  This feature marks our series of river valleys.  Another aspect making our terrain unique was our idea of putting the depression feature above our sea level plane.  We built up a large mountain feature towards the middle of our allotted area, then formed a depression in that mountain, making it look like a caldera. Beyond the mountain is where the plain and the hill reside.  Below are two pictures that show a view of our terrain from each end of the plant box.

     For our coordinate system, we decided to mark off each direction by increments of 5 centimeters.  To do this we simply held a tape measure across the edges of the plant box and marked off each increments directly on the wooden box with a sharpie.  Those measurements became our x and y coordinates.  At each coordinate, we then took a measurement of the elevation at that point, creating the z coordinate.  To take these measurements in the more simple areas, it was sufficient enough to hold up a meter stick and approximate where our elevation level was.  As we worked our way across our terrain, the complexity grew.  We needed to change our technique in order to get more accurate readings of the z value.  To do this, one person held a meter stick perpendicular to "ground surface" and another person held a meter stick parallel to the ground surface at the correct height corresponding to that features' elevation about zero.  Another person read off the measurement from the first meter stick to ensure that each person could concentrate on holding their meter sticks straight and in the correct place.  The photo below can help illustrate how we did this.

More accurate way of measuring the complicated terrain.

Discussion

     We started the day with very ambitious intentions.  Our caldera feature was very high above our zero elevation level, which we wanted in order to show interesting digital models later.  We hadn't realized how difficult it would be to measure this kind of feature given the tools we had to do it.  This was especially true for the depression feature in the mountain/caldera.  Our methods did work, but things would have been easier given a more simplistic terrain.  Given a minimal amount of tools, I think our group took useful survey data.

Conclusion

Rite in the Rain field notebook to record data before we acquired a lap top.

     After spending five hours outside in the Wisconsin winter weather, we had over 1000 points of data for the terrain we had built in a 110 cm x 235 cm plant box.  We had a large range of elevation data collect, the lowest elevation being 17 cm below our sea level, and the highest elevation at 37 cm above our sea level.  The next step is to ensure all of our data is in an Excel spreadsheet then import it into ArcGIS.  From there, we can run different kinds of terrain analysis on the data.