Balloon Mapping II

Balloon Mapping II

Introduction

This week we set out to improve upon our aerial photography skills via balloon mapping again. This week we got lucky and had significantly less wind to work with and this would prove key to attaining high quality, usable photographs. We took a lot of lessons we learned last week and tried to act accordingly this week. We lost our balloon from last week when the rope snapped so we had to work with a completely new balloon this time around. We also took care to secure our balloon so we wouldn’t lose it again through another freak accident.



Figure 1:An ovierview of our study area. We were looking to map as much of campus as possible

Methodology

Following in last weeks steps, we split into different groups and completed our individual tasks before descending on the garage out by Phillips to fill our balloon. Once we filled the balloon we again walked out to Phillips mall and launched our balloon. (Figures 2, 3)



Figure 2: One of the first images taken from our balloon camera as it takes off



Figure 3: A good image for photo mapping. Notice the angle at which the camera is facing the ground is almost directly straight down.

 

This week however, I had a different task. A select few members of the class were in charge of taking ground control points with 3 Trimble Juno units. We went around campus and took ground control points at various light posts and trashcans and other landmarks.

The purpose of the ground control points was to have something to reference to later when we added the photos to ArcMap we could georeference these photos and the landmark on the image, to the gps coordinates we collected. This gives the pictures a ‘place’ in the real world so they have the utmost accuracy.

I was not a part of the launching or walking of the balloon since I was taking ground control points but you can refer to any of my classmates blogs for the narrative of that event. (http://people.uwec.edu/hupyjp/webdocs/geog336_Reports_spr13.htm)

Once we returned inside the images were uploaded to the computer and we could begin to search for usable ones. (Figure 3 shows a good example of a very usable photo.
 

Results/Discussion

Overall the pictures were far better quality than last week’s images and we were able to cover a lot more of campus, AND most importantly we returned with our balloon in hand.

Once we sorted through the images we realized that as a class we had far more areas to cover than one single person could stitch together. My innovative classmates decided to split up the study area into our 6 groups so that we could each stitch a little piece of it. Then ideally we could stitch our mosaics together to make a large image of all of campus.

This week we mosaicked with a different tool. In order to provide a more accurate orthophoto we decided to use ArcMap to do the mosaicking. This allowed us to add ground control points to our images.

Within arc map, you need to add a basemap to the project. This will allow you to assign points on our collected pictures, to the points on the base map. Then ArcMap can attach a geographical location to each picture. If you add enough of these points to each picutre you can avoid distortion as well as provide a highly accurate mosaicked image. It's all pretty simple within arcmap. You simply open your georeferencing tool and then add the individual pictures to the map. then you can select each picture, add reference points, and then the program stitches it together for you.
 (Figures 4, 5 show the final georeferenced area)

Figure 4: Overiew of the geo referenced photo area. It appears 'rough' in some areas because of all the recent changes in campus area buildings.

 

Figure 5: Same area as previous figure, but a bit bigger.

Conclusion

Overall this was a great addition to last week’s activity. All the things that went wrong last week, seemed to go right this week. We were able to use a new different software to stitch together a section of our study area and with more spatial accuracy than the first time. This was a great exercise to practice our mosaicking skills and teach us how we could do low cost aerial mapping of nearly any type of study area.