Working with and understanding Geospatial Data

Introduction

Briefly described, geospatial data is any data referring to a specific position on earth. For example, this could be a house, trees, mountains, and buildings. The spatial component for most geographic data is geographic coordinates, latitude, and longitude.

What differentiates an ordinary digital map from data in GIS is that GIS is more or less something that professor Joseph Hupy refers to as a "smart map". Integrated with the digital map, there is a database with attribute data. To see an example, click the hyperlink of hurricanes through time.

Having a notion of geospatial data is fundamental when working with UAS data for numerous reasons. UAS is deeply involved in keeping track of earthly positions. The geographical information one can extract from a single image is mindboggling. Today, most companies, maybe unknowingly, rely heavily on geospatial data in their everyday business activities. Customer address records, customer locations, and areas of interest linked to sales, are all considered geographic data.

There are two basic types or forms of geospatial data: vector and raster. The vector format uses points, polylines, and polygons to represent spatial features such as buildings and roads. The less complex raster format uses pixels to represent spatial features.

This lab will focus on how one can apply UAS data into ArcMap. Different features and a more hands-on approach to understanding the concepts of how coordinates work will be demonstrated.

Methods/Lab Assignment

Why is file management so key in working with UAS data?
In a GIS-file, there are multiple file types. The different file extensions for the Tornado-file is shown in Figure 1. When working with UAS-data one will gather a lot of information. In order to separate them, using file management is key.

Figure 1.

ArcCatalog

What is the purpose of establishing a folder connection?
What is the difference between viewing the files in Arc Catalog vs. Windows explorer?
Why is it so important, beyond maintaining proper file management/naming, to use Arc Catalog for managing your GIS data?

During the semester we will have space at the server in order to save and access a file that we are going to use. Having an own folder will facilitate to locate the data one is searching for. But the most important things, as one can see below in Figure 2, is that each shapefile includes a lot of information. The information from Figure 1 is all covered in a single shapefile, in this case, TORNADO_tracks.shp in Figure 2. Using the ArcCatalog will keep track of the important files, but without losing any data. The information one wants to work with is transparent and easily accessible when adding files into the ArcMap.

Figure 2

What do those icons mean?

These are all vector data. The icons to the left of the text displays if it is a single point, polylines or polygons in that direction:

What topic/term relates to this description tab?

This all relates to metadata.

Why is having this information so important in the UAS realm?

This information is crucial for geospatial technology to work. The planning phase and ultimately making decisions is based on metadata. Examples of UAS metadata could be; pilot, flying date, UAS platform, sensor type, altitude, Ground Control coordinates, and UAS coordinates.

What does it say?

The "20170613_wolfpaving_dsm.tif" in the Wolfpaving_X5 folder is stating that "Statistics have not been calculated".

What types of tasks rely on statistics?

Statistics is important when performing certain tasks on imagery. For instance, applying a contrast stretch or different types of classifications.

Min elevation of the DSM:    281.04708862305

Max elevation of the DSM:   323.08865356445

Mean elevation of the DSM: 296.9669108356

Why would this information be important for data processing, analysis, and communication with the client? 

The client could be a company and in order for them to make good decision making, they need statistics. UAS will provide companies with a bunch of statistics which they can use for various interests.

Cell Size (X,Y): 0.02077, 0.02077

Format: TIFF

XY Coordinate System: WGS_1984_UTM_Zone_16N

Linear Unit: Meter

Datum: D_WGS_1984

Pixel size in square cm: 2cm*2cm = 4cm^2

ArcMap

One way of adding data to ArcMap is by using the in-ArcMap ArcCatalog and dragging a shapefile to the screen and it will show up as a layer. Another way is to have ArcCatalog open in another window and drag it into ArcMap. Also, there is a third way to open the desired data, and that with a shortcut button with the name "Add data".

What basemap did you use? Why?
I choose to open a Street map cause my goal was to choose an easy-navigated map. I thought that maybe choosing a map, which displays streets in an easy manner could be good.

What type of GIS data is this? This is Polygon data. Each polygon in Figure 3 represents a specific state.

Figure 3: Polygons

What type of GIS data is this? The tornado data is represented through vector polylines as shown in Figure 4:

Figure 4: Polylines of tornadoes

Figure 5: Zoomed in polylines

What type of GIS data is this? Adding the "dams00x020.shp" new vector points appear representing dam locations. In Figure 6, one can clearly see that some points have been added to the base map:

Coordinate systems for the three layers:

Tornado_tracks: 

Projected Coordinate System (PCS): NAD_1983_UTM_Zone_16N

Geographic Coordinate System (GCS): GCS_North_American_1983

Dams: 

Geographic Coordinate System (GCS): GCS_North_American_1983

States:

Projected Coordinate System (PCS): USA_Contiguous_Equidistant_Conic

Geographic Coordinate System (GCS): GCS_North_American_1983

Are all of these coordinate systems the same? Why might that be an issue?

The tornado tracks and the states layers have different PCSs. Using two different coordinate systems can and will cause problems. Using different framework when determining real-world locations, will place global attributes on different spots and provide misleading information. A physical location on Earth has a different coordinate value in a different GCS. When these layers do not refer to the same coordinate system, a datum transformation needs to be executed.

How might the need for metadata relate to coordinate systems?

The metadata should illustrate what kind of coordinate system is used. It is of highest interest to know what coordinate system is used. a GCS uses a 3D spherical surface to define locations on Earth, while a PCS defines a flat 2D surface. Among other, what differs these two is that a PCS has constant lengths and angles across the map plane.

Think of some different types of attribute data that could be used in conjunction with UAS data and list it here with a useful example. UAS data that could be useful in a GIS-environment and added into the attributes table would, for instance, be flight height, the flying date, flight pilot, sensor type, what kind of coordinate system etc. This refers to the metadata.

What type of data is this? This is raster data with 4 different bands. Every pixel represents a single value (integer). 

What is the format? The orthomosaic file extension is TIFF, which is preferred format cause it keeps the information lossless.

What is the projection? The projection coordinate system here is UTM, which provides a mechanism to project maps onto a 2D Cartesian coordinate plane (XY).

Figure 7: illustrates the transparent mosaic layer of Wolfpaving

What is the projection? This is a UTM-projection from zone 16N.

Does this projection match the Ortho? The orthomosaic shapefile is also a UTM-projection,

Why is this so important? The reason why this is important has been stated above.

Do the points line up with the markers on the ground? As Figure 8 illustrates it seems like the ground control points are well placed to the markers but as one zooms in, one finds out that there is a deviation. As displayed in Figure 10, the accuracy was about 10 centimeters from where it was supposed to. This makes sense since we from the metadata found out that every pixel was 2 cm long and from the image, it looks like the deviation is 5 pixels. From the image, it looks like it is a bit steep, which could play in.

Figure 8

Figure 9

Figure 10

Measure tool: Measure several features on the map. How might this type of tool be useful in working with UAS data? This is a tool that one can use to find distances between objects, like above for example. In Figure 11 the one can also choose area if that is preferable. One can choose different units like meters and inches.

Figure 11

Identify tool: Use the identify tool on several of the GCP points. Also, turn on the DSM and identify pixels on that layer. How might this tool come in handy when working with UAS data? This tool will be very useful to find specific locations on the Earth. As Figure 12 shows, both East, North and the height is displayed.

Figure 12

Swipe tool: Use the swipe tool to move between the Orthomosaic and the DSM. How might this tool be useful when working with UAS data? Beneath in Figure 13, the swipe function is illustrated. This will come in handy to separate between Digital Surface Models and other kinds of Digital Elevations Models.

Figure 13

Conclusions

Like illustrated in this post it is obvious, using UAS data gives the GIS-user various opportunities to display maps and adopt geospatial technology into their own specific needs. However, concerns do exists. When pairing points from the UAS data to the ground, the accuracy and quality is not interesting if the coordinate system is totally off. Using UAS data in combination with Forestry brings a lot of interesting options.