Introduction and
Background:
For
this lab, the objective is to simply digitize a handful of real-world features
into a GIS by using a Global Positioning System (GPS). Martin Goettl and the UWEC Geography Department
provided the students with Trimble Juno handheld GPS units with which we would
collect point, polyline, and polygon features nearby on campus. Before collecting the data, we will need to
familiarize ourselves with geodatabase construction and deployment of a
geodatabase to a mobile device using ESRI ArcMap and ArcPad. Finally, we are going to import the data back
onto the computer and develop a cartographically pleasing product which shows
three trees and lightposts, three triangular plots (which will turn to lawn in
the spring), a nearby circular sidewalk feature and the nearby bridge.
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| fig 1 The Juno. Pulled from the interweb, this was not my exact Juno. It is the right model though. Virtually identical. |
Methods:
Step
one is to develop a geodatabase using the Arc platform. In our case, using ArcCat 10.1, this is
accomplished by right clicking on the folder where the database will be stored,
then under ‘new’ either “File-” or “Personal Geodatabase” is selected (fig 1). Using a similar method, but clicking this time
on the database, three new feature classes were developed: one point, one line
and one polygon. The feature classes
were created using the NAD83 Wisconsin HARN in meters because it is a fairly
accurate projection which is common throughout the state. Also created was a field for each labeled “type.”
The ArcPad Data Manager extension in ArcMap
was then used to export the data to the Juno device.
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| fig 2 adding a geodatabase |
With
the important information loaded onto the handheld GPS, it was taken outside to
collect the required feature data. Before
doing so, it needs to be ensured that the GPS unit’s almanac is up to date and
if it needs updating the user should be sure to do so (fortunately, mine was
fully updated). To digitize the data, I
used point averaging to collect the lights and trees (points) as well as the
vertices of the triangles and circle. Instead of using point averaging, I tried a
tracklog for the bridge over the creek (which collected my position at points
over a time interval).
Finally,
the data was uploaded to the computer using the Data Manager described earlier.
As a couple of triangles had extraneous
vertices, possibly from user error, I edited these points out of the data. It was then symbolized and made into a map.
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| fig 3 My raw data was contaminated by extra vertices. They could either be GPS burps, or user error. It is impossible to say for certain. |
Results and
Discussion:
Completion
of the project itself required relatively few steps), though learning to
successfully navigate the foreign ArcPad controls was something of a headache
for myself, which perhaps led to my interesting polygon features (fig 3). This can be easily fixed in the Juno unit or in ArcMap though. If I were to redo the project, I would definitely
rely on point averaging for the path across the bridge, because -not
surprisingly- the tracklog does not provide as accurate data as the point
averaging. This is not to imply that the
average of ten points with the small Juno unit is necessarily accurate, because
as can be seen in the final result it is not.
Well, it is to a point. That
point just happens to be small features such as the smaller triangles and
circle. In fact, I am a little surprised
that my circle is as circular as it is.
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| fig 4 My final Presentation |
The background aerial imagery given
for the project was a year or so old, and had not been updated to reflect the
fact that a fairly large neighboring building had been demolished, and a
replacement built to its south. The
sidewalks over the area have been completely altered, and another completely
new building in the north is in the process of going up, so the features I
processed seem fairly out of place on the given image. I pulled a more recent image from another
class which was aerially mapping campus and had taken an image less than a week
before I digitized the features. The
difference in the presentation of the final project is staggering.
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