Due to the complex nature of balloon mapping, the task was
broken up into two parts that spanned over two weeks of class. The first week,
outlined by this blog, entailed experimentation with the mapping rigs created
in week three. The purpose of experimenting with the different rigs prior to
collecting the final imagery that would be used to create a seamless, mosaicked
map of campus was to observe how the rig behaved when deployed to 400 feet and
troubleshoot any problems that may arise. Preliminary methods of how images
generated from the balloon mapping rig are to be processed and mosaicked will also
be outlined and discussed.
Methods
Because of the short window of time
that spanned our three hour class period that required the assembly, transport,
launch and retrieval of the rig; delegation of duties was essential. The class
was broken up into small groups (one-four people) who were assigned to be responsible
for a single element of the rig launch. To document all aspects of the
experimentation day, fellow classmate Tonya O. was outfitted HD video camera to
provide video footage.
The rig used for balloon mapping
would resemble the HABL platform. The Styrofoam box would hang from the helium
filled weather balloon and would house a Lumix digital camera that was set to
continuous shoot mode. Also tested within the same rig housing was a Flip
Camera that was set to shoot video. Connecting the balloon/ camera rig to the
pilot on the ground would be 400 feet of rope that was marked off in 50 foot increments
to allow for observation of the balloons altitude. Once the balloon reached its
service altitude of 400 feet, the time was observed to be compared to date
stamps on the pictures to confirm the camera rig was shooting imagery at the
correct altitude. Once deployed the pilot controlling the balloon from the
ground was to experiment with different flight paths by walking around the
campus courtyard.
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| Figure 1: Shown here are teammembers inflating the weather balloon used for the mapping of campus with helium. |
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| Figure 2: Shown here is the balloon mapping rig suspended from the helium filled weather balloon. |
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| Figure 3: Shown here is the balloon mapping rig at its maximum altitued (around 100ft). Notice its horizontal drift from being directly overhead due to the wind out of the NW. |
Imagery generated by this
experimental launch were to be mosaicked using three different approaches outlined
by Dr. Hupy. The methods to be tested were a freeware website called
Mapknitter, a geospatial raster processing software program called ERDAS
Imagine, and ArcMap Image Processor. For each of the programs, imagery was
uploaded as .jpeg files.
Our Team consisting of Tonya O. and
Chuck P. stitched the balloon imagery together using Mapknitter. After
uploading an image into Mapknitter, tools within the program allowed for image
manipulation. Once uploaded and projected over a Google Earth basemap of the UWEC campus tools
such as rotate (to scale the image), distort (to shift the image by dragging
the corners), and toggle (to adjust image transparency) were used to manipulate
the image to mimic that of the basemap.
Discussion
After much discussion as a class, we
decided to use a rig similar to the HABL platform instead of the plastic bottle
prototypes generated for lab three in class. By incorporating the HABL rig into
the balloon mapping exercise, testing for both could be done simultaneously. The
first observation that was made was that the camera would have to be firmly
secured within the Styrofoam rig housing to prevent the lens from slipping out
of the slot cut into the bottom of the rig due to any turbulence encountered at
400 feet. The second observation made was that nearly windless conditions would
be necessary to both get the balloon to reach 400 feet directly overhead, and
to also keep the camera steady to prevent it from swinging like a pendulum.
Although the line connecting the balloon to the ground snapped from such high
winds, we decided that higher pound test line would not be necessary when
flying it in calmer conditions. Any image that was taken as the camera was
swinging would obviously be blurry, but also it would be oblique because it was
not pointed directly downward; thus useless for image mosaicking. Although windless
conditions would be optimal for image collection with the balloon, we observed that
the addition of some sort of fin on the bottom of the rig would help mitigate
its effect and allow us to fly the rig even if there was a slight breeze. It
was also decided that the Lumix digital camera would be used because after processing
the images from both the Flip camera and the Lumix, the Lumix took higher
quality imagery.
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| Figure 4: Shown here is a low oblique image of UWEC taken by the rig as it swung out of control underneath the balloon. |
Aside from observations made from
the experimental flying of the balloon, many were also made in regard to image
processing. I found Mapknitter to be extremely straightforward and user friendly
but I was not able to achieve the level of accuracy needed for this project by
using it to mosaic the images. Although it generated cartographically pleasing
maps, it lacked the georeferencing component needed to tie our imagery to
ground control points which is our end goal, so either ERDAS Imagine or ArcMap
Image Processor will be used for mosaicking the second time. Both programs
allow for georeferencing so either will suit our needs.
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| Figure 5: Shown here is the mosaic output from MapKnitter overlayed on a Google Earth base map. |
Conclusion
Even though Mother Nature won out and
snapped the line at the base of the balloon due to such extreme wind
conditions, we were able to gather valuable data that will be applied to the
final launch of the balloon mapping rig. By applying the knowledge gained by this
experimental day, I have no doubt that a seamless, high resolution mosaicked map
of campus will be generated.
Shown in the video above is the balloon rig plummeting into the river when the 400 foot tether snapped at the base of the balloon.
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