Cartographic Fundamentals

 Cartography

Understanding cartography and its fundamentals are an essential aspect of processing UAS data. As mentioned in previous posts, you can collect all of the data in the world but it means nothing if you do not have an effective means to display it. In this lab, I was tasked with taking a dataset and applying various tools such as DSMs and hillshades. After that, I took the data and created a map for each one with various cartographic components. In this post, I will explain and describe those components and why they are important for UAS data.

How does a map differ from an image?

A map has many visual components that make it differ from an image. These aspects create a visual infographic that helps to explain what is being displayed in the image. Giving an individual an image, especially an image captured with a drone, would probably confuse them and not get their intention past a simple glance. With a map, the individual will be able to see the image and understand what is going on and decipher the data. Here are some of the biggest components that a map should contain that will help it deliver.

• Locator Map - To show the area (on a larger scale) that is being displayed.
• Detailed Insets - These are zoomed-in frames of a specific object in the image such as a GCP.
• Title - This gives an overall quick description of the map.
• North Arrow - For applicable maps, this will help give a sense of orientation.
• Scale - This helps to give a sense of size.
• Watermark - Displays who created the map

Working with the data

Now that we understand the components it is time to turn various images/datasets into a readable map. However, the first thing that needs to be done is to take a look at the metadata. Metadata is a detailed look into the flight information. Metadata is important for every flight because it gives detailed information like the altitude, aircraft, date, sensor, etc. It is crucial that this information is copied down after every flight and held for records. Metadata is especially important when there are various members of the crew performing different tasks. If an individual of my flight crew handed me the images from their mission and asked me to process them into an orthomosaic, I might be able to, but it would be much easier with the above data. Below is a table that outlines the metadata for the flight we are processing.

Date Flown	June 13th, 2017
Platform	M600 Pro
Sensor	Zenmuse X5
Altitude Flown	70m
Ground Control GPS	Trimble UX5
Ground Control Coordinates	UGS84 UTM Zone 16
UAS Coordinates	WGS 84 DD
Pilot	Peter Menet

(Figure.1 Metadata Table)

The next concept that we learned in this lab was working with DSMs. A DSM is a digital surface model which shows the elevation values for all aspects of an image including cars, trees, signs, etc. This differs from a digital elevation model that only shows the surface elevation values. For UAS data we want a DSM because it gives us more depth for analysis. Digital surface models can be complemented with various shading tools that highlight different features in the images. Below are images of the tools we used.

The DSM in figure 1 uses a color ramp in order to highlight some of the elevation values for the area. The legend in the top left shows the spectrum for the elevations and their respective colors. The DSM was created with images from a dredging operation. The large areas of orange are the piles of material that are being created.

(Figure.2 Shaded DSM)

Figure 3 is a shaded aspect. You can see that the elevation is shown more sharply compared to the DSM above. A downside is that the key aspects like the buildings and piles are hard to differentiate which can cause issues. However, if the client simply wants pure elevation then this would be perfect.

(Figure.3 Shaded Aspect DSM)

The next map is of a shaded slope. This one does not show elevations as well as the others above but it does give some detail into the key objects like buildings. The bright white ring is a large tank that can be easily seen. 

(Figure.4 Shaded Slope)

Digital surface models are amazing at showing elevation values for an image but what happens when a client wants an actual image? This is where orthomosaics come in. Orthomosaics take multiple images and stitch them together to create one large detailed image. This can be done with hundreds or even thousands of images. Orthomosaics offer very high detail to the point where one can see small cracks in the ground even from 400 feet above. Below is a map created with an orthomosaic of the same area as above.

(Figure.5 Orthomosaic)

As you can see, I was able to create insets of the GCPs by zooming in fairly far. The detail of the insets are still high quality and you can see the spray paint for the GCPs.


Reflection

Spatial patterns of data can tell the reader much more information than what the image shows inherently. Patterns such as shaded slope, shaded dsm, and shaded aspect can show elevation levels of various images. In this lab, we took a DSM and added multiple hillshades which highlighted the higher and lower points of elevation. Furthermore, we took an orthomosaic and created insets with great detail to show ground control points. In future projects and jobs, we will collect data via unmanned aircraft and be tasked with turning those images into meaningful data. The objectives of this lab are a solid foundation for teaching us the basics of cartography. Cartography is an important aspect of UAS data because it allows us to create very detailed maps and display information. The maps above can be delivered to a client that wants aerial information about their dredging operation. ArcGIS Pro offers an array of tools that help to turn images into maps.