Building Maps With UAS Data

Being a UAS student at Purdue, I occasionally find myself being given opportunities to experiment with new things.  A professor of mine offered me a chance to get to learn the data processing side in his lab.  I ultimately ended up crating a cartographic map from the data set and compiled a list of FAQ’s that should give ideas on what separates data processing from aerial photography.

  • Why are proper cartographic skills essential in working with UAS data?

Cartographic skills are a critical component of managing UAS data.  Without proper measurements and ground control points, the data gathered is only functional as ‘pretty pictures’ and holds no quantitative data.  Quantitative data can only be collected by creating a map with metadata.

  • What are the fundamentals of turning either a drawing or an aerial image into a map?

Creating a map from aerial imagery requires a coordinate system to be present.  This can be done using lat/long coordinates or a more local coordinate system.

  • What can spatial patterns of data tell the reader about UAS data? Provide several examples.

Spatial patterns can be analyzed to create a topographic map of a local area.  This can be particularly useful for surveying areas where potential landslides are possible.  Similarly, the DEM can be used to measure the volume of hills which is of particular interest in mining industries.

  • What are the objectives of the lab?

The lab was created to introduce us to the data analysis side of UAS.  The lab uses the data created from the orthomosaic and combines it with ground control points and other metadata to set up a GIS that can be queried.

  • What key characteristics should go into folder and file naming conventions?

Caution should be used when naming the files in the folder.  The files are all named with the location and coordinate system as well as a brief description of what the file is.

  • Why is file management so key in working with UAS data?

Some UAS data projects can become very data intensive with hundreds or thousands of files.  For this reason, file management is critical to being able to properly find data at a later date.

  • What key forms of metadata should be associated with every UAS mission?

Every mission should include the coordinate system used, the altitude flown, and the platform and sensor used to gather the data.

  • What basemap did you use? Why?

I used the World Light Grey canvas because of its easy to view contrast and the fact that the ground control points show well on the map.

  • What is the difference between a DSM and DEM?

A Digital Surface Model is a height map with the datum being the lowest point in the map and representing 0ft of elevation.  A Digital Elevation Model is similar but instead places the elevation datum at sea level.

  • Why are the statistics Cell Size, Units, Projection, Highest Elevation, and Lowest Elevation important?

These pieces of information show the scale of the map in each of the directions.  For example, the highest and lowest elevations show the scale of elevation change while the cell size and units state horizontal scales of the map.  The projection identifies how the map is being created and therefore how the map will be distorted.

  • What does hillshading do towards being able to visualize relief and topography?

Hillshade adds a color gradient to the DSM so elevation changes can be more easily identified.  

  • How does the orthomosaic relate to what you see in the shaded relief of the DSM

The orthomosaic allows the cartographer to create a map in color which can be more easily compared against the DSM to interpret high and low areas.

  • What is the purpose of vertical exaggeration? What settings do you have for your data?

Vertical exaggeration sets the scale of what color should be used to show the lowest point and the highest point of the DSM.  If too little vertical exaggeration is used, the color difference may be difficult to see.

  • What color ramp did you use? Why?

I chose to use the inverted red to green diverging dark ramp because of its easy interpretation of elevation change.

  • What are the advantages of using ArcScene to view UAS DSM data vs. the overhead shaded relief in ArcMap. What are the disadvantages?

ArcScene is a visualization tool which makes it very easy to see the changes in elevation.  It does however have limitations in that it can’t add metadata into the map such as scales or titles.

  • Is this export a map? Why or why not?

The export from ArcScene is not a map because it lacks metadata.  There is no scale listed and it doesn’t define a coordinate system.

  • Summarize what makes UAS data useful as a tool to the cartographer and GIS user

UAS data is very detailed and offers extremely high resolution imagery when compared to a satellite.  It also offers greater temporal resolution which can be used for analysis of a region of interest over time.

  • What limitations does the data have? What should the user know about the data when working with it.

The data is often very large and can be difficult to process.  For this reason, the data analyst will need a computer or server with decent amounts of power to keep up with the demanding processing.

  • Speculate what other forms of data this data could be combined with to make it even more useful.

UAS data can be combined with the data from satellites to identify areas where higher resolution is needed.  It can also be combined with spectrometer measurement data when doing multispectral flights to calibrate the ranges of the camera.  GPS data from ground control points can also be used to improve the positional accuracy of the map.

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