Geospatial Basics: Working with and Understanding Geospatial Data
Introduction:
Geospatial data is data that references its position relative to the earth’s surface. It contains locational components in the form of coordinates that reference the data to the earth. There are two main geospatial coordinate systems: Geographic Coordinate Systems (GCS) and Projected Coordinate Systems (PCS). GCS use a three-dimensional spherical surface, angular units of measure, and latitude and longitude coordinates to locate points on the sphere (or spheroid). PCS reference the GCS however it projects it onto a flat, two-dimensional surface where linear units of measure (meters, centimeters, feet, inches, etc.) are used to locate specific points. While PCS may be very useful, they do have some drawbacks, because they distort certain aspects of a map such as direction, shape, area or, proximity.
What makes data in a GIS different than a digital map?
GIS is a ‘smart map’ where different aspects of the map can be queried, filtered, and manipulated. These aspects are called attributes, containing information about specific points, pixel values, lines, areas, etc that the viewer wishes to investigate.
Why is having an understanding of geospatial concepts and geospatial data so fundamental to working with UAS data?
Without the understanding of geospatial concepts, how they work, what their limits are, and their quirks, one is hampered in the ability to collect, process, analyze, and manipulate data. As an example, if one does not understand the difference between projected and geographic coordinate systems and collects ground control points (GCPs) in one of these coordinate systems then flies a drone that collects data using the other, when trying to use the data to rectify the images, the difference between the two could be off by a substantial margin making any rectification inaccurate.
What are some of the key geospatial concepts and fundamentals that this lab addresses
Understanding the difference between GCS and PCS, how to navigate ArcMap and ArcCatalog, the different types of files and how they differ from each other, and the ‘smart’ aspects (attributes) of GIS data.
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.
ArcCatalog
What is the purpose of establishing a folder connection?
The purpose of establishing folder connections in ArcCatalog is to organize the data around different information types, so one can easily access the relevant data set one is working on without having to sort through files for the correct one. This is shown in figure 2.
What is the difference between viewing the files in ArcCatalog vs. Windows explorer?
The files viewed in ArcCatalog show whether they are a raster file or a shape file, such as a point file, polyline file, or polygon file. When viewed in Windows File Explorer, one cannot determine these aspects without first opening the files.
Why is it so important, beyond maintaining proper file management/naming, to use ArcCatalog for managing your GIS data?
ArcCatalog mixes files and merges certain files into one in ArcCatalog, whereas File Explorer does not; so when opening data directly from File Explorer, certain aspects may not be displayed.
What do those icons mean? Hint: Use the preview tab to view the file.
The icons indicate whether the file is a raster file, text file, point file, polyline file, or polygon file. Below is figure 3 showing images of these geospatial data types along with examples of each.
Within each of the files above there is a section containing key information called metadata. This metadata can be made visible by clicking on the description tab in ArcCatalog.
Why is having this information so important in the UAS realm?
Metadata is essential in making sense of a UAS data set. Without it the data set is useless as the metadata describes all the conditions in which the flight took place; such as altitude, coordinate system of the imagery, coordinate system used to measure the ground control points, sensor type, sensor overlap, time of day, sky condition, reflectance calibration values, sun angle, and much more. While not all of these may be used in one flight, a majority of these conditions are absolutely essential in gathering good useable data.
Of almost equal usefulness are the statistics values generated in ArcCatalog. To view them, expand the Wolfpaving_X5 folder. Right click on the 20170613_wolfpaving_dsm.tif raster, and then select properties then scroll down to the statistics section.
What does it say?
In this case it says "No Statistics Calculated." if this the case, exit the section, right click on the file properties again and click on "Calculate Statistics." If one were to hover over calculate statistics, a small information window stating what types of tasks rely on statistics.
What types of tasks rely on statistics?
In this case the information window listed applying a contrast sketch and applying a classification to data.
Once calculated, the statistics for 20170613_wolfpaving_dsm.tif listed the minimum, maximum, and mean elevation within the Digital Surface Model (DSM). Below are listed these values:
Why would this information be important for data processing, analysis, and communication with the client? (Think of what was discussed in lecture/demo)
It could allow checking of the accuracy of the data when processing and could allow the client to keep tabs on contractors to keep them honest as to how much earth was removed from a particular site when excavating.
There is even more useful information listed in the window along with the statistics. The list includes:
Methods/Lab Assignment:
Working with the Data
Windows File Explorer
When viewing the files in Windows File Explorer, the data is organized into groups by type of geospatial data with each group containing different file types as shown below in figure 1. |
| Figure 1: Files Within One Geospatial Data 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.
ArcCatalog
What is the purpose of establishing a folder connection?
The purpose of establishing folder connections in ArcCatalog is to organize the data around different information types, so one can easily access the relevant data set one is working on without having to sort through files for the correct one. This is shown in figure 2.
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| Figure 2: ArcCatalog Folder Connections |
What is the difference between viewing the files in ArcCatalog vs. Windows explorer?
The files viewed in ArcCatalog show whether they are a raster file or a shape file, such as a point file, polyline file, or polygon file. When viewed in Windows File Explorer, one cannot determine these aspects without first opening the files.
Why is it so important, beyond maintaining proper file management/naming, to use ArcCatalog for managing your GIS data?
ArcCatalog mixes files and merges certain files into one in ArcCatalog, whereas File Explorer does not; so when opening data directly from File Explorer, certain aspects may not be displayed.
What do those icons mean? Hint: Use the preview tab to view the file.
The icons indicate whether the file is a raster file, text file, point file, polyline file, or polygon file. Below is figure 3 showing images of these geospatial data types along with examples of each.
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| Figure 3: Geospatial Data Icons and Specific File Examples |
Why is having this information so important in the UAS realm?
Metadata is essential in making sense of a UAS data set. Without it the data set is useless as the metadata describes all the conditions in which the flight took place; such as altitude, coordinate system of the imagery, coordinate system used to measure the ground control points, sensor type, sensor overlap, time of day, sky condition, reflectance calibration values, sun angle, and much more. While not all of these may be used in one flight, a majority of these conditions are absolutely essential in gathering good useable data.
Of almost equal usefulness are the statistics values generated in ArcCatalog. To view them, expand the Wolfpaving_X5 folder. Right click on the 20170613_wolfpaving_dsm.tif raster, and then select properties then scroll down to the statistics section.
What does it say?
In this case it says "No Statistics Calculated." if this the case, exit the section, right click on the file properties again and click on "Calculate Statistics." If one were to hover over calculate statistics, a small information window stating what types of tasks rely on statistics.
What types of tasks rely on statistics?
In this case the information window listed applying a contrast sketch and applying a classification to data.
Once calculated, the statistics for 20170613_wolfpaving_dsm.tif listed the minimum, maximum, and mean elevation within the Digital Surface Model (DSM). Below are listed these values:
- Min DSM Elevation = 281
- Max DSM Elevation = 323
- Mean DSM Elevation = 296
Why would this information be important for data processing, analysis, and communication with the client? (Think of what was discussed in lecture/demo)
It could allow checking of the accuracy of the data when processing and could allow the client to keep tabs on contractors to keep them honest as to how much earth was removed from a particular site when excavating.
There is even more useful information listed in the window along with the statistics. The list includes:
- Cell Size (X,Y): 0.02077, 0.02077
- Format: TIFF
- XY Coordinate System: WGS_1984_UTM_Zone_16N
- Linear Unit: Meter (1.000000)
- Datum: D_WGS_1984
- Use the Linear unit and write the pixel size in square cm: 2.077cm x 2.077cm = 4.31cm^2
ArcMap
In ArcMap, in order to get started using the program, one must add data. One can add data by clicking on File then clicking on Add Data, by clicking on the sand colored diamond icon with a black plus located next to the map scale, or by dragging a file from the ArcCatalog tab located on the right side of the ArcMap screen. The very first data set added was a basemap.
What basemap did you use? Why?
For the purposes of this exercise, the basemap chosen was a topographic map as it included streets, towns, and topographic data. Figure 5 below shows the topographic basemap chosen.
Once the topographical map was added, the states.shp shapefile was added from the Tornadoes folder and the reference basemap was turned off as it could slow down the computer. See Figure 6 below.
What type of GIS data is this? Justify your answer.
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| Figure 5: Topographic Basemap |
Once the topographical map was added, the states.shp shapefile was added from the Tornadoes folder and the reference basemap was turned off as it could slow down the computer. See Figure 6 below.
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| Figure 6: States Shapefile |
The states shapefile is a polygon file as each state is an enclosed shape with an area within which the data attributes for that state is contained.
Once the states shapefile was added, the TORNADO_tracks.shp file was added.
What type of GIS data is this? Justify your answer.
The tornado shape file is an example of a polyline file and all attribute data of these tornadoes is contained within each of the lines that represent them. If one clicks on one of these lines, the attributes for that particular tornado will appear (see figure 8).
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| Figure 8: Tornado Polyline File with Attributes |
After opening the Tornado polyline file the dams00x020.shp shapefile was added from the hydrofeatures folder.
What type of GIS data is this? Justify your answer.
The hydrofeatures shape file, see figure 9, is an example of a point file where each hydrofeature is represented by a single point with individual associated data attributes.
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| Figure 9: Hydrofeatures Point File with Attributes |
Once all the files mentioned above were opened, the coordinate systems of each file were recorded by right clicking on the file then clicking on properties and navigating to the source tab. These Coordinate systems are listed below:
- TORNADO_tracks file coordinate system: NAD_1983_UTM_Zone_16N
- Dams00x020 file coordinate system: GCS_North_American_1983
- States file coordinate system: GCS_North_American_1983
Are all of these coordinate systems the same? Why might that be an issue?
The Dams00x020 file and the States file both used the GCS_North_American_1983 coordinate system while the TORNADO_tracks file used the NAD_1983_UTM_Zone_16N coordinate system. GCS_North_American_1983 is a geographic coordinate system that uses angular distances to find specific points referenced by the dam and state files to create their shapes whereas the tornado file references the NAD_1983_UTM_Zone_16N coordinate system which uses a linear unit of measure by taking the globe and flattening it out into a projection with different segments called zones. The use of these two different coordinate systems together will cause the dam and state data to be misaligned.
The Dams00x020 file and the States file both used the GCS_North_American_1983 coordinate system while the TORNADO_tracks file used the NAD_1983_UTM_Zone_16N coordinate system. GCS_North_American_1983 is a geographic coordinate system that uses angular distances to find specific points referenced by the dam and state files to create their shapes whereas the tornado file references the NAD_1983_UTM_Zone_16N coordinate system which uses a linear unit of measure by taking the globe and flattening it out into a projection with different segments called zones. The use of these two different coordinate systems together will cause the dam and state data to be misaligned.
How might the need for metadata relate to coordinate systems?
If one does not have the metadata stating what type of coordinate system is being used, the data cannot be fit together well sets as it will be skewed.
After the coordinate systems were viewed, the attribute data was viewed for the TORNADO_tracks file by right clicking on the file and selecting attribute data. Figure 10 below shows this attribute data.
After the coordinate systems were viewed, the attribute data was viewed for the TORNADO_tracks file by right clicking on the file and selecting attribute data. Figure 10 below shows this attribute data.
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| Figure 10: TORNADO_tracks Attribute Data |
Attribute data can be used used in conjunction with UAS data to aid in mission planning such as viewing the location of roads and their condition where one is operating for the purpose of planning landing zones for a fixed wing UAS.
After examining the attribute data and learning how to navigate ArcMap, specific UAS data was added and examined. The files that were opened were an orthomosaic and DSM located in the Wolfpaving_X5 folder. Once opened, the DSM was turned off and the orthomosaic and associated information. See figure 11 and questions below.
What type of data is this?
After examining the attribute data and learning how to navigate ArcMap, specific UAS data was added and examined. The files that were opened were an orthomosaic and DSM located in the Wolfpaving_X5 folder. Once opened, the DSM was turned off and the orthomosaic and associated information. See figure 11 and questions below.
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| Figure 11: Wolfpaving_X5 Orthomosaic |
A Raster file with 3 bands and integer values for red, green, and blue.
What is the format?
TIFF
TIFF
What is the projection?
Universal Transverse Mercator, specifically WGS_1984_UTM_Zone_16N.
Once the previous questions were answered, the XYWOLF_PAVING_UTM16_massaged.shp file was added and the questions were answered.
What is the projection?
Universal Transverse Mercator, specifically WGS_1984_UTM_Zone_16N.
Universal Transverse Mercator, specifically WGS_1984_UTM_Zone_16N.
Once the previous questions were answered, the XYWOLF_PAVING_UTM16_massaged.shp file was added and the questions were answered.
What is the projection?
Universal Transverse Mercator, specifically WGS_1984_UTM_Zone_16N.
Does this projection match the Ortho? Why is this so important?
Yes. If the points and marks on the ground do not line up, the data is not representative of what is actually there.
To check how well the projection lined up with the image, the orthomosaic was zoomed in on over a few of the GCP points. See figure 12
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| Figure 12: Orthomosaic overlaid with Projection |
Do the points line up with the markers on the ground?
yes
yes
ArcMap Tools
After the GCPs were overlaid, a few of the tools in ArcMap were investigated.
Measure: Several features were measured using the measuring tool
An example see figure 13.
How might this type of tool be useful in working with UAS data?
Measure: Several features were measured using the measuring tool
An example see figure 13. |
| Figure 13: Measuring Tool Example |
The measure tool shown here can allow the measurement of certain aspects of the data including distance and area. This can be helpful when for example, one needs to check the size (area) and position of objects in real life so that it can be compared with plans. It can also allow people to measure objects that are not on said plans so they may be added.
Identify: The identify tool
was then used to investigate several of the GCP points.
How might this tool come in handy when working with UAS data?
The identify tool allows the user to query attribute data of specific data on the smart map. An example of this would be to view the specific attributes of a particular tornado in Indiana as seen in figure 8 and 9 above.
was then used to investigate several of the GCP points.How might this tool come in handy when working with UAS data?
The identify tool allows the user to query attribute data of specific data on the smart map. An example of this would be to view the specific attributes of a particular tornado in Indiana as seen in figure 8 and 9 above.
Swipe: The swipe tool
was next used to move between the Orthomosaic and the DSM. Figure 14 shows the swipe tool in action. |
| Figure 14: Swipe Tool Example |
The swipe tool depicted here allows the user to compare the differences between multiple layers.
Conclusions:
What makes UAS data useful as a tool to the GIS user?
It can allow the GIS user to get overhead views of an area with relative ease using multiple different sensor packages to gather different types of data such as RGB, NIR, infrared, and LiDAR. The UAS data enables a more up-to-date and accurate means of ascertaining what is happening on a small scale and communicate it with a client.
What limitations does the data have? What should the user know about the data when working with it.
What other forms of data this data could be combined with to make it even more useful?
It can allow the GIS user to get overhead views of an area with relative ease using multiple different sensor packages to gather different types of data such as RGB, NIR, infrared, and LiDAR. The UAS data enables a more up-to-date and accurate means of ascertaining what is happening on a small scale and communicate it with a client.
What limitations does the data have? What should the user know about the data when working with it.
- When viewing and working with the data, files become large very quickly and can require additional storage space. These large files can slow down the computer when viewing too many at the same time. In addition, when one is processing large data sets the processing time can be very long because they are very resource intensive.
- When one is working with the data, the attributes that the user utilizes or creates can be as simple or as complex as the user wishes.
- When using a GIS program the program may be costly to acquire and depending on the program if it is a cloud based program, the company may own your data and may be able to sell it to a competitor.
What other forms of data this data could be combined with to make it even more useful?
- Aviation airspace charts and LAANC information as a UAS preflight planning process to examine the type of airspace one will be operating in.
- Satellite and UAS data to get a larger overview of an area as well as high resolution imagery of specific areas.
