Why are proper cartographic skills essential in working with UAS data?
Being able to make a cartographically pleasing representation of the area of interest is very important. A viewer should be able to look at a map and understand what it is representing and where it is. It should also have important information on where the data came from and when it was gathered.
What are the fundamentals of turning either a drawing or an aerial image into a map?
The data can be imported into a program like ArcMap and put into a geodatabase.
What can spatial patterns of data tell the reader about UAS data? Provide several examples.
Spatial patterns can tell the reader a number of things, for example, if looking at UAS data of a crop field and the crops in one area of the field are yielding less growth and production, that could mean the soil is not as good there or less water is getting to that area. Having a birds eye view of the area of interest gives the opportunity to discover patterns that are not so easily recognizable from the ground.
What are the objectives of the lab?
The objective of this lab is to create a map that demonstrates good map building fundamentals and data management.
Methods
To create a map the first thing that needs to be done is bringing the data into a program that can work with it. An orthomosaic and a Digital Surface Model (DSM) were brought into ArcMap of the outdoor track on the UW-Eau Claire campus taken from a DJI Phantom drone at 50m. These files were then turned into functioning maps, three maps were created. The first map is an orthomosaiked image map to show what the area looks like from above in standard RBG imagery. An orthorectified mosaic (orthomosaic) is an image that is actually tied to the coordinate system, This is constant throughout the image and eliminates distortion . A georeferenced mosaic is similar to an orthorectified mosaic but it is not actually tied to the coordinate system, it is juist dies down by reference points and can still be distorted. Many people publish georectified images to be orthorectified when that is not true. The second map is a Digital Surface Model that shows the elevation changes of the track and the surrounding area. A Digital Elevation Model shows the elevation of the ground level, this comes from the last returns of the data. A Digital Surface Model shows the elevation with trees and other objects that are not the surface of the terrain. The third map is a hill shade model shows the shadows of the DSM, this is exaggerated and hows elevation even more. This was done in ArcScene by giving the DSM vertical exaggeration.
Figure 1: Orthomosaic Map of Sports Track
Figure 2: DSM
Figure 3: Hillshade Relief Map
Results
The orthomosaic (figure 1) gives a good idea of what the area of interest looks like but in order to understand in more depth of the area of interest other maps and models were created. To understand elevation in the AOI, a DSM was created (figure 2). The DSM shows that from the southwest portion of the map to the northeast portion, the elevation slowly increases. This aligns with the statistics from the DSM descriptive stats by staying in the proper range from 17-23. Using the DSM and the orthomosaic, more can be understood about the AOI. To understand even further, the hillshade map shows that there are buildings, trees and other vegetation surrounding the map. This also explains some of the descriptive statistics.
Conclusion
UAS data is very useful as a tool to a cartographer and a GIS user because it enables the user to get high quality data from a specific area of interest in a short amount of time and for little cost. Getting centimeter level accuracy from a satellite image would be nearly impossible and very expensive. The limitations of this data is that it comes with a lot of extra data that needs to be cut out. The user needs to know how to do various tasks to get the data into a form that is useful. UAS data could be combined with other data to make it extremely useful. In this situation, rainfall and water run off analysis could be done with the additional elevation, soil type, and other information.
References
http://resources.arcgis.com/en/help/main/10.2/index.html#/Fundamentals_of_orthorectifying_a_raster_dataset/009t000000ms000000/
http://resources.arcgis.com/en/help/main/10.2/index.html#/Fundamentals_of_georeferencing_a_raster_dataset/009t000000mn000000/
