Introduction
There are many techniques used to
conduct an accurate survey on a plot of land. With the advancement of
technology, surveys can be done using GPS technology and survey stations,
however one cannot always rely on technology to complete the task. This study
conducts a basic survey technique using distance and azimuth as the principal
recordings. Several of the criteria includes surveying out a quarter hectare
plot of land on UW Eau Claire’s campus and gathering a minimum of 50 points
with simple survey instruments. This project will include a description of the
surveyed study area, a breakdown of the methods, and the accuracy assessment of
the survey results.
Study Area
One of the study’s criteria requires
a survey of a ¼ hectare plot of land or a parcel of 50 meters by 50 meters anywhere
on UW Eau Claire’s campus. My group member and I chose to do the southeast
corner of the Hibbard Parking Lot as our survey site as it includes a variety
of different features. These features include street signs, parking signs,
trees, bushes, stop lights, houses, light posts, and many more different types.
The site was also chosen because the campus is undergoing construction of the
new education building and from the new davies center, which is not shown on
recent aerial maps of the university. The Hibbard parking lot has many of the
same features as the Phillips Parking lot, which was mapped in our field
methods class for an in class activity a week prior. The only differences
between these two locations is that our study area does not have art
sculptures, however it has more street signs and features from residential
homes because of its adjacency to state street and Eau Claire’s third ward
neighborhood. Figure 1 shows an aerial view of the surveyed study area that
encompasses a quarter hectare.
Figure
1: Southeast Corner of Hibbard Parking Lot Study Area
Methodology
There are many steps in conducting a
distance azimuth survey of an area. This study gave the class an opportunity to
be paired in groups of two and survey a 50 by 50 meter area of UW Eau Claire’s
campus using simple surveying equipment. This project is laid out in the following
methods: gather the survey materials, conduct the actual survey at the study
area location, enter and organize the data into Microsoft Excel, Import it into
ArcMap and manipulate the data using the tools in ArcToolbox, and superimpose
point data over an aerial image of the surveyed area to assess accuracy.
The materials needed in the survey
process include the following: TruPulse 360 laser rangefinder, compass, pen,
and paper. The main instrument that was used during the survey is the TruPulse
360 laser rangefinder, which measures standard distance and azimuth for each
feature in the study area shown in Figure 2. Although these were the two
measurements that our group recorded with this device, it also provides other
measurement solutions such as vertical distance, angle of inclination, and
other types that can be used in a more detailed survey. The magnetic compass is
another instrument that we utilized on some of the features. This tool is used
in surveying to find the azimuth of the features and requires the need to adjust
for magnetic declination. Magnetic north, the point at which the planet’s
magnetic field points vertically downward, is always moving and is also not the
same as true north, which stays fixed in one spot. Magnetic declination is the
angle that measures the difference between true north and magnetic north and
varies depending on where one is located on the planet. The rule of thumb for
adjusting it on the compass is to subtract an east variation and add a west
variation. The city of Eau Claire is 0.58° west thus 0.58° must be added to it
to equal 0°.
Figure
2: TruPulse 360 Laser Rangefinder
The
next method is to go out to the study area and survey the site in a 50 by 50
meter parcel. The point of origin is shown in Figure 3 as a sign with a cement
base, which was chosen because it is a permanent feature and it could easily be
distinguished on an aerial map. As aforementioned, the standard distance and
azimuth were measured using the laser instrument to conduct the survey. Standard
distance is measured in meters to each feature from the point of origin.
Azimuth is defined as the horizontal direction expressed as the angular
distance between the direction of a fixed point (point of origin where the
observer stands) and the direction of the object. The survey consists of 50 data
points of the features in the Hibbard parking lot ranging from street signs to
trees. Since the Hibbard parking lot has not gone through any major changes in
the past few years, most of these features that were surveyed should show up on
an older aerial map.
Figure
3: Parking lot sign representing the Point of Origin
After the field work has been
conducted and the measurements for the survey have been recorded, the next step
is to enter the data into Microsoft excel shown in Figure 4. The excel
spreadsheet includes six fields: point ID, origin x coordinate, origin y
coordinate, standard distance, azimuth, and point description. The x and y
point of origin coordinates were found by adding an aerial basemap by bing in
ArcMap and clicking the exact feature with the identify button after zooming in
to the study area. This gave the location in decimal degrees, which could be
copied and pasted in excel. The point of origin coordinates are the same for
every point in the spreadsheet. After this step is completed, the cells under
the x and y columns have to formatted to display at least 6 decimal places. This
is done so that the point of origin is located on the exact spot of the feature
(Figure 3) that we designated to be our observing point on the aerial map.
Figure
4: Excel spreadsheet of surveyed data points
The next method is to import the
data from excel to ArcMap. However, before the data is imported, it is
necessary to create a new geodatabase for this table. This will not only help
maintain the data, but it will also make the tools in ArcMap run smoother. It
has occurred in the past that not storing data in a geodatabase could bring
problems when running some of the tools in the software.
Once the data is imported into
ArcMap, a series of tools are utilized to display all of the recorded features
spatially. The first tool is called Bearing Distance to Line, which is found
under data management and features in ArcToolbox. This tool shows the bearing distance
from point of origin to the feature (Figure 5) by creating a geodetic line to
each point that was recorded with the TruPulse 360 Laser. Feature Vertices to Points
is the other tool, which is also found under data management and features in
ArcToolbox. The tool creates a new feature class of points that are generated
from vertices or the endpoints of the bearing distance lines shown in Figure 6.
Figure
5: Bearing Distance to Line Feature Class
Figure
6: Feature Vertices to Points Feature Class
The
last method is to superimpose point data over an aerial image of the surveyed
area. Even though this has no effect or alteration on the study area, the added
aerial image was taken before the construction of the new Davies center
sometime in the summer of 2010. Having the image overlay the data makes it
possible to assess the accuracy of the survey. Figure 7 shows the final map of
the study area after the application of the two tools in ArcMap.
Figure
7: Superimposed Image overlaying Surveyed Study Area
Discussion
The distance azimuth survey
technique proved that it can work for almost any geographical location as long
as the features are viewable from the point of origin. An advantage of this
survey approach is that a researcher does not need to rely on technology to
conduct a survey in the field. Although technology has its advantages, it can
fail at any given moment thus creating a risk of wasted time and effort in the
field only to yield no results from it. Another advantage is that this method
can be used anywhere and it is easy to move the equipment around because of the
small size and weight. However, a disadvantage of using this technique is
risking the accuracy of the survey. There are many factors that result in human
errors, which may affect how accurate the survey is. When my group was
conducting the survey with the laser pointer, we noticed it was hard to hold
the instrument still to shoot at an object close to 50 meters away from the
point of origin. This most likely resulted in the laser either shooting right
past the object or landing short by a few meters.
Although
this survey technique has been utilized for many different types of
environments, it has been replaced mostly by growing technology such as GPS and
survey stations, which use more sophisticated equipment. These new techniques
also produce fairly accurate results compared to the distance azimuth
technique. In Figure 7, it is evident that some of the points collected in the
survey are off by a few meters in certain locations. Even though we recorded features
that lined the sides of the State and Garfield intersection, some of the points
on the map appear to be on the actual street pavement. This could be from the
human error associated with this type of survey technique. Overall the distance
azimuth survey showed that it can be convenient to use in many geographical
settings, however after displaying the results our group found that it is not
as accurate compared to other techniques.
Conclusion
The goal of the study is to survey a
50 by 50 meter parcel of land on UW Eau Claire’s campus by utilizing a TruPulse
360 laser rangefinder and a compass. Although there are many advantages to
using this survey technique, the results of our survey were inaccurate in some
locations in the study area. Despite the slight inaccuracy, I have taken a lot
out of this experience by learning how to conduct a survey over a large parcel
of land by using a simple handheld laser and compass and displaying the results
in ArcMap to show the results.
No comments:
Post a Comment