Introduction
The goal of this activity was to explore the basics of image gathering using a simple helium balloon and picavet rig apparatus. Originally this activity was to be completed using a large kite, however the activity began with very low wind conditions therefore making a balloon a better option. By using one of the most simple methods of aerial photography and data collection, we were able to gain an appreciation for modern unmanned aerial vehicles which can be programmed to survey a given area automatically.
The goal of this activity was to explore the basics of image gathering using a simple helium balloon and picavet rig apparatus. Originally this activity was to be completed using a large kite, however the activity began with very low wind conditions therefore making a balloon a better option. By using one of the most simple methods of aerial photography and data collection, we were able to gain an appreciation for modern unmanned aerial vehicles which can be programmed to survey a given area automatically.
Study Area
This activity was carried out at the Eau Claire Soccer Park in Eau Claire, Wisconsin. The facility, consisting of mainly soccer fields, indoor sports complex and a parking lot, also contained a concessions building, small playground and a basketball court. A picture of the study area is provided below courtesy of google earth. The weather changed from overcast with calm winds at the beginning of data collection to overcast with a light rain and stronger winds to the West near the end of data collection. The goal was to survey the whole area between the sports complex on the West end to the tree line on the East end, however, the weather conditions in the end did not allow for the completion of this goal.
This activity was carried out at the Eau Claire Soccer Park in Eau Claire, Wisconsin. The facility, consisting of mainly soccer fields, indoor sports complex and a parking lot, also contained a concessions building, small playground and a basketball court. A picture of the study area is provided below courtesy of google earth. The weather changed from overcast with calm winds at the beginning of data collection to overcast with a light rain and stronger winds to the West near the end of data collection. The goal was to survey the whole area between the sports complex on the West end to the tree line on the East end, however, the weather conditions in the end did not allow for the completion of this goal.
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Figure 1: The area studied is outlined in red with the red arrow depicting the direction of North |
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| Figure 2: Inflating the balloon with helium |
Methods
The first step in collecting the data for this activity was the assembly of the necessary apparatus. The first step in this process involved inflating a large balloon (Figure 2) with helium which would lift the camera rigging and GPS into the air. The balloon was filled until to a point where it had enough buoyancy to lift the camera rigging, GPS and tether into the air with ease. Once it was determined that this criteria was met, the balloon was removed from the helium source and the neck of the balloon was folded over a metal ring while one person pinched right above the ring so as to not release any helium from the balloon in the process. This metal ring would be used to tie the tether to.
Two zip-ties were then tightly fixed above the ring, holding the folded over balloon neck tight so that helium would not escape and the ends of the ties were clipped off to avoid any danger of them puncturing the balloon, while giving the balloon a nice, clean look. Finally a long tether from a spool was attached to the ring to be used to adjust and maintain the height of the apparatus.Figure 3 depicts the final product of the balloon set up.
The next apparatus in need of assembly was the picavet rig. A picavet rig is a system consisting of an X-shaped platform for mounting camera/GPS equipment attached to series of cords used to stabilize the platform and is used in aerial photography to mount a camera to objects such as a kite or in our case a balloon (see figure 4 for usual picavet design). The picavet rig we used (Depicted in figure 5) contained a metal platform with two camera mounts and a strip of Velcro in the middle to attach the yellow GPS. The hook of the rig were attached to the tether of the balloon several feet below the ring and was leveled out so that the cameras were facing straight down at an angle of 90 degrees, also known as nadir.
The two cameras on the picavet rig were cannon point and shoot digital cameras, one regular camera and one that was modified to be partially infrared, and both had CHDK or Cannon Hacker Development Kit firmware installed on it. What CHDK does is modify the camera on top of its original functionality to allow the user to take time lapse photos or photos at a set rate. This is especially useful for aerial photography when you cant be in physical contact with the camera for an extended period of time. For our purposes while walking with a balloon, we decided to take pictures every 6 seconds. With a faster aircraft you could modify that time to take pictures faster since you will be covering more area faster, or you can set up your camera in a way to take pictures in increments dependent on a certain distance you travel. Both cameras were set to this setting and once they began taking pictures, the balloon was raised 100' into the air. A DJI Phantom drone was used to capture the video below of the rig in action.
When the balloon was at it's maximum height, we began walking the field starting at the East edge and moving North to South. At the end of the field we paced out 30' to the West and began walking the opposite direction until the end of the field (beginning of a sidewalk). Again we paced 30 feet to the West and proceeded back the opposite way we came. The purpose of going only 30' to the West instead of pacing out the entire focal range of the camera was to allow for enough overlap in the pictures so that they could be stitched together and analyzed This process continued for about an hour when we reached the concession building and it began to rain. At the end we walked back to our base in the parking lot and disassembled the rig.
The first step in collecting the data for this activity was the assembly of the necessary apparatus. The first step in this process involved inflating a large balloon (Figure 2) with helium which would lift the camera rigging and GPS into the air. The balloon was filled until to a point where it had enough buoyancy to lift the camera rigging, GPS and tether into the air with ease. Once it was determined that this criteria was met, the balloon was removed from the helium source and the neck of the balloon was folded over a metal ring while one person pinched right above the ring so as to not release any helium from the balloon in the process. This metal ring would be used to tie the tether to.
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| Figure 3: Final set up of balloon apparatus |
Two zip-ties were then tightly fixed above the ring, holding the folded over balloon neck tight so that helium would not escape and the ends of the ties were clipped off to avoid any danger of them puncturing the balloon, while giving the balloon a nice, clean look. Finally a long tether from a spool was attached to the ring to be used to adjust and maintain the height of the apparatus.Figure 3 depicts the final product of the balloon set up.
The next apparatus in need of assembly was the picavet rig. A picavet rig is a system consisting of an X-shaped platform for mounting camera/GPS equipment attached to series of cords used to stabilize the platform and is used in aerial photography to mount a camera to objects such as a kite or in our case a balloon (see figure 4 for usual picavet design). The picavet rig we used (Depicted in figure 5) contained a metal platform with two camera mounts and a strip of Velcro in the middle to attach the yellow GPS. The hook of the rig were attached to the tether of the balloon several feet below the ring and was leveled out so that the cameras were facing straight down at an angle of 90 degrees, also known as nadir.
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| Figure 4: Usual picavet set up http://www.kapshop.com/How_To/index.php?page=picavet-lacing |
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| Figure 5: Picavet rigging used in our activity |
When the balloon was at it's maximum height, we began walking the field starting at the East edge and moving North to South. At the end of the field we paced out 30' to the West and began walking the opposite direction until the end of the field (beginning of a sidewalk). Again we paced 30 feet to the West and proceeded back the opposite way we came. The purpose of going only 30' to the West instead of pacing out the entire focal range of the camera was to allow for enough overlap in the pictures so that they could be stitched together and analyzed This process continued for about an hour when we reached the concession building and it began to rain. At the end we walked back to our base in the parking lot and disassembled the rig.
Discussion
The vertical or nadir view images that were captured are especially helpful for measuring and mapping the area of study. At this point in the curriculum we have not yet discussed how these images can be processed and interpreted, and they have yet to be stitched together, but below in figures 6 and 7 you can see the different types of photographs that were taken in both visible light and near infrared both of which have their own advantages.
Visible light imagery is useful for plotting a map using colors people are more familiar with and gives the imagery a google earth "satellite view" feel. The near infrared imagery, while still able to be stitched together to form a recognizable map has purpose way beyond being a unique looking picture. Infrared imaging can be used to discover many things such as monitoring plant growth/health, the heat radiating off the rooftops of homes, and even detecting oil spills. With this near infrared photograph you can use the colors of the plant life as a baseline and use subsequent imagery on a later date to visualize a change in infrared light to monitor changes we wont be able to see with only visible light.
The next data that was collected was from the GPS module that was also attached to the picavet. This data was plotted into a Google Earth file to show the path that the balloon was taking while we were walking the field.
From these pictures we can see that the path the balloon was not a straight vertical line, which could cause problems with image stitching on top of the fact that the camera was not fixed, but allowed to freely spin during data collection. Also note that the spacing started to expand halfway through. This was the point in data collection where we began to worry about the rain and sped things up by spacing our paths out. Spacing the lines out could also provide it's own challenges with image stitching. In figure 9, you can see that the plot on Google Earth is in fact three dimensional. This depicts the altitude of the picavet rig at any given time during collection, which is an interesting feature to note.
The vertical or nadir view images that were captured are especially helpful for measuring and mapping the area of study. At this point in the curriculum we have not yet discussed how these images can be processed and interpreted, and they have yet to be stitched together, but below in figures 6 and 7 you can see the different types of photographs that were taken in both visible light and near infrared both of which have their own advantages.
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| Figure 6: Visible light imagery |
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| Figure 7: Near infrared imagery |
Visible light imagery is useful for plotting a map using colors people are more familiar with and gives the imagery a google earth "satellite view" feel. The near infrared imagery, while still able to be stitched together to form a recognizable map has purpose way beyond being a unique looking picture. Infrared imaging can be used to discover many things such as monitoring plant growth/health, the heat radiating off the rooftops of homes, and even detecting oil spills. With this near infrared photograph you can use the colors of the plant life as a baseline and use subsequent imagery on a later date to visualize a change in infrared light to monitor changes we wont be able to see with only visible light.
The next data that was collected was from the GPS module that was also attached to the picavet. This data was plotted into a Google Earth file to show the path that the balloon was taking while we were walking the field.
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| Figure 9: Example of the 3D nature of the Google Earth Plot |
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| Figure 8: Google Earth map depicting the route of data collection |
From these pictures we can see that the path the balloon was not a straight vertical line, which could cause problems with image stitching on top of the fact that the camera was not fixed, but allowed to freely spin during data collection. Also note that the spacing started to expand halfway through. This was the point in data collection where we began to worry about the rain and sped things up by spacing our paths out. Spacing the lines out could also provide it's own challenges with image stitching. In figure 9, you can see that the plot on Google Earth is in fact three dimensional. This depicts the altitude of the picavet rig at any given time during collection, which is an interesting feature to note.
Conclusion
Image gathering with a simple aerial apparatus like the balloon used in this activity has both its advantages and disadvantages. On the downside, the camera equipment isn't fixed and therefore freely swings and spins in the air making image stitching (I'd assume) more difficult than using a straight flying airplane with a fixed camera. Another down side is the balloon apparatus would probably only be practical in an open field setting as the stings could be easily tangled in an area with trees or larger structures. On the plus side, however, this apparatus is simple, way cheaper than a drone that could carry the equivalent equipment and an easy introductory method for collecting aerial photographs. That being said, now that I have an appreciation for the process of collecting aerial photographs, I look forward to learning more advanced methods and how to process the collected data. Stay tuned!
Image gathering with a simple aerial apparatus like the balloon used in this activity has both its advantages and disadvantages. On the downside, the camera equipment isn't fixed and therefore freely swings and spins in the air making image stitching (I'd assume) more difficult than using a straight flying airplane with a fixed camera. Another down side is the balloon apparatus would probably only be practical in an open field setting as the stings could be easily tangled in an area with trees or larger structures. On the plus side, however, this apparatus is simple, way cheaper than a drone that could carry the equivalent equipment and an easy introductory method for collecting aerial photographs. That being said, now that I have an appreciation for the process of collecting aerial photographs, I look forward to learning more advanced methods and how to process the collected data. Stay tuned!
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