Building Maps with UAS Data

Introduction: 

Why are proper cartographic skills essential in working with UAS data?
            Cartographic skills enable one to be able to organize and filter the data so that when one communicates with the client, it is easy to understand which can have a large impact on perceived expertise and professionalism.

What are the fundamentals of turning either a drawing or an aerial image into a map?
            In order to turn an image into a map, it must include a scale bar, north arrow, locator map, watermark of who created the map, the data sources and, metadata.

What can spatial patterns of data tell the reader about UAS data? 
            Spatial patterns allow the reader of the data to determine where areas of interest are in relation to other areas. Without spatial patterns to locate data relative to other data, the reader will have difficulty using the data to make useful analyses. For example, if one were to map a particular mountain but misplaced or didn't record the geospatial coordinates of the imagery, one would have difficulty accurately locating the the data in space and comparing it to the surrounding terrain.

What are the objectives of the lab?
            The objectives of this lab are to learn how to clarify digital surface model DSM data using ArcMap with hillshade, how to create a cartographic map with ArcMap and, how to use ArcScene to manipulate DSMs.

Methods/Lab Assignment:

Working with the Data:

What key characteristics should go into folder and file naming conventions?
            When naming folders and files, folder names should go from general to specific while file names should be relatively specific with a date (organized by yyyy-mm-dd), the project name (use meaningful abbreviations) and, the file type.

Why is file management so key in working with UAS data?
            When working with UAS data, good file management is key in keeping the data organized in a clear logical manner as files tend to be large and contain key metadata that if misplaced, could cause the data set to be incomplete, inaccurate, or not openable at all.

What key forms of metadata should be associated with every UAS mission?
            When flying a UAS mission, key metadata that should be recorded includes the location, date, time, aircraft platform used, sensor flown, altitude flown, name and coordinate system of the ground control GPS, coordinate system of the sensor, coordinate system of the aircraft platform, image overlap and sidelap settings, visibility, sky conditions, wind and, the pilot’s name. Below is table 1 which provides the key metadata for the data that will be worked with during this lab.

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Table 1: Key Metadata for Wolfpaving_X5

            In addition to key metadata, certain additional metadata is highly recommended to capture as it may be useful in processing certain data. This additional metadata includes the time flown, flight duration, image overlap and sidelap, sky conditions, sun angle and, wind.


            ArcMap
            The first step in this lab after recording the flight metadata was to open ArcMap, add a basemap, and save the project in the Lab3_Building a map with UAS Data folder.

What basemap was used? Why?
            The topographic basemap was used as it shows the features of the surrounding environment such as lakes, rivers, towns, etc... When one zooms in, it includes contour lines of the surrounding terrain. Figure 1 below shows surrounding features and contour lines as compared to the digital surface model DSM with hillshading applied.

Figure 1: DSM with Hillshading and Topographic Basemap

            Once the topographical basemap was added, the 20170613_wolfpaving_dsm.tif DSM and 20170613_wolfpaving_transparent_mosaic_group1.tif orthomosaic were added and the statistics were calculated for the DSM. Table 2 below shows the statistics for the 20170613_wolfpaving_dsm.tif DSM.

Table 2: 20170613_wolfpaving_dsm.tif Statistics 

            In addition to the calculated statistics, certain other important descriptive statistics pertaining to the DSM were recorded and displayed below in table 3.

Table 3: Descriptive Statistics

Why are these important?
            Descriptive statistics can provide useful information such as the ground resolution, pixel size, the type of coordinate system used and the highest and lowest elevation values of the data. This can aid in correctly processing the data, adding GCPs and, investigating the data.

What is the difference between a DSM and DEM?
            A digital surface model DSM and a digital elevation model DEM are similar in that they both show the features and relationships between features on the Earth’s surface. The difference between the two is that a DSM includes all the buildings, trees, bushes etc., while a DEM shows only the surface terrain features. Because a DEM shows the terrain, it is sometimes referred to as a digital terrain model DTM.  Below, figure 2 compares a DSM to a DEM (DTM) of the same area.

Figure 2: DSM and DEM/DTM Comparison.
Image source: www.http://www.gisresources.com/confused-dem-dtm-dsm/

            Once the previous steps and answers were completed, the next task was to generate a hillshade for the Wolfpaving DSM, apply a color ramp to the DSM and, overlay the two.
What does hillshading do towards being able to visualize relief and topography.
It increased the ability to see areas of detail that were hidden before. Figures 3 and 4 show difference in a particular area between the plain DSM and the DSM with hillshading.

Figure 3: DSM Without Hillshading

Figure 4: DSM With Hillshading

            Next, the hillshaded DSM was compared to the orthomosaic using the swipe tool.

How does the orthomosaic relate to what you see in the shaded relief of the DSM?
            Having the overlay of the hillshaded DSM over the orthomosaic helped visualize the height of various features on the orthomosaic. For example, a certain hillmound that in the orthomosaic appeared flat, was not (See Figure 5).

Figure 5: Hillshaded DSM Compared to Orthomosaic

            ArcScene
            The next software used in this lab was ArcScene. ArcScene is a 3-dimensional visualization software that allow the Wolfpaving DSM to be manipulated and explored. First, the DSM was added and the base heights were set to their elevation values. Then the vertical exaggeration was adjusted.

What is the purpose of vertical exaggeration? What settings do you have for your data?
            The purpose of setting the vertical exaggeration is to increase or decrease the changes in terrain so that features may become more apparent or become more muted to the viewer. In this case, the exaggeration chosen was a factor of 1.5.

What color ramp did you use? Why?
            The color ramp used was Condition Number because it brightly highlighted the elevation changes from low, depicted in green, to hight, depicted in red.

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

• An advantage of using ArcScene is that the viewer can move around a DSM and inspect it at various angles, or perform drainage modeling on it.
• A disadvantage of using ArcScene is that it is more difficult to create a map using it.

            Once the all the settings were adjusted, the image was exported and is shown in figure 6 below.

Figure 6: ArcScene Wolfpaving DSM Looking NW with 1.5 Exaggeration

Is this export a map? Why or why not?
            No, this is not a map as there is no scale bar, no north arrow, locator map, watermark, or data source.

Building a Map

            The next and final portion of the lab assignment was to create a map (or series of maps) of the DSM and orthomosaic that each had a north arrow, scale bar, locator map, watermark, data sources and, metadata (sensor, altitude, UAS platform, pilot). Figures 7 and 8 below are maps of the DSM and orthomosaic respectively.

Figure 7: Wolf Creek Paving DSM Map

Figure 8: Wolf Creek Paving Orthomosaic Map

Conclusion:

What makes UAS data useful as a tool to the cartographer and GIS user?
            It can allow the cartographer to gain high temporal resolution and high ground resolution (relative to satellite imagery) view of an area, allowing them to create DEM, DSM and, orthomosaic maps of said area relatively cheaply (relative to scouting with aircraft) and easily.
 
What limitations does the data have? What should the user know about the data when working with it.
            In order to work with the data, one has to have an understanding of how to operate the sometimes unintuitive software.

            The user should be aware that the geospatial software used in this lab can be quite costly.
One should have a good grasp of what geospatial data is, how to use it and, some of its particulars such as different coordinate systems. See my previous blog post below on geospatial basics for more information.

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

• The 3-dimensional DSM in ArcScene could be used to model water flow and areas at risk of high erosion.
• The DEM of a localized area could be combined with a DEM created a particular city for planning purposes.