Monday, May 13: Handheld GPS

Introduction:

                This semester’s last exercise will be based on digitization of real world features with a handheld GPS unit. For it, we will be returning to the Priory and dividing into groups of three that will navigate the land in order to collect field data from three different categories of information.  This is the same property that has been traversed by the class four times over the course of the semester, and from experience we know that it has a number of trails crisscrossing well over one hundred acres of wooded hills. 

Figure 1: The Priory

               The goal of this project is to prepare and deploy a geodatabase which employs domains and ranges to assist in data collection, then after collecting the data to import the information found into a GIS and display a professional-level map of what was found in the field.  Furthermore, information that was considered of potential importance to the project was determined and collected with the location of material collected in the GPS.  The trio in which I was digitizing data selected benches, erosion, and the invasive species buckthorn to collect and analyze data from.

 Methodology:

                The first task in our final adventure is to develop a geodatabase that can be deployed to a mobile GPS unit for data collection.  For this, the typical steps in developing a geodatabase in ArcMap were followed (as outlines in earlier posts), along with the creation of a point feature class for benches, erosion, and invasive species.  For each, domains were developed and included in the geodatabase in order to improve and speed data collection.  For bench data, the quality or condition of the bench was included (as useable, useable but needs repair, or unusable).  With the invasive species of buckthorn as well as erosion, the amount encountered was included in the data collection as well (low, medium, high).  Finally, a notes field was included to each feature class to provide an outlet that could record any unforeseen but still important or useable data collection.

fig 2: Creating a Domain

fig 3: Setting a domain in a feature class

                After developing these domains, the ArcPad Data Manager Extension was used to import this geodatabase to the chosen GPS unit.  In addition to returning to the Priory for this project, the final installment of our field methods class includes the return of the Trimble Juno handheld GPS unit (fig 4) which was what the database was uploaded to before heading into the field.  This process was simplified by the “Get Data for Arc Pad” wizard, activated by clicking the “Get Data for Arc Pad” button on the ArcPad toolbar (fig 5).  This program helps guide a user through selection of which data to export to the Juno, along with photograph options for feature classes and output options and extraction criteria.

fig 4: the JUNO

                Data collection was a fairly straight forward process:  our group simply set out a path which trekked through the priory following a major foot path and digitized the locations of our selected features as we encountered them.  Being that none of the selected features were continuous, each individual group member decided to collect each feature in the event of problems arising with the data collected by one (or two) of the group members.

figure 5: the ArcPad toolbar
First button with arrow is to deploy to a GPS, button with left arrow is to import from 

Finally, once satisfied with the data collected it was returned to the GIS and prepared into a map that displayed the data collected by feature.  The importing was also done through a wizard accessed from the tool bar called “Get Data from ArcPad” (fig 3).  Esri doesn’t fool around with the names for their tools, which is nice because it makes them easier to use.   After completing the steps outlined by this program (which merely consist of selecting the data to upload onto the computer), the data was successfully imported and manipulated into a useable map.

 Results:

fig 6: the Final Product

The first takeaway that I had from this exercise, and the first bit of advice that I have for any trying to recreate it, is to know your technology.  Twice the technology failed my group in this exercise, first in my attempts to upload my database to a GPS unit that was known to be faulty (unbeknownst to myself), and again when my team member Joey was mysteriously unable to acquire a satellite fix with his Juno unit.  Countless minutes of my life were washed away in a futile effort to do something that would not ultimately be done, and an opportunity to gather data was similarly wasted by the technology failing to work.  I could not help but appreciate the irony that the final project done in this class harkened back to one of the very first lessons imparted on us by professor Hupy: don’t trust technology, if it can fail, it will and often at the worst possible times.  Fortunately, Brandon and I had also been collecting data that would otherwise have been Joey’s domain, and the group successfully completed the task of mapping three different features at the Priory.

Another takeaway would be that the handheld GPS is not always the most accurate data collection unit, especially when the sky is obscured by trees.  While much of the data collected by Brandon and myself matched closely, some simply did not and this combined with the earlier paragraph is a lesson in the limitation of GPS data and a reminder about the importance of knowing how much you are willing to trust the data given to you.