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What are the names of 4 fields in this data file?Name, X, Y, and Z.Do you know what the numbers and units are for each field? Speculate what each field contains in terms of the information and units of measure.X = latitudeY = LongitudeZ = AltitudeHow does the concept of metadata relate to the dearth of information here?The dataset given to us provided very little metadata. The only information given was the location and the coordinates for the GCPs and datums.Move the mouse over the center of the map and write down the coordinates in the space below. What is the X coordinate? What is the Y? What is the latitude? What is the longitude? In what order are they listedX = longitude= -99.412410Y = latitude= 40.526056They were listed in this order.Does this appear to be a projected or unprojected coordinate system? How can you tell?Unprojected because the spatial reference is GCS_WGC_1984.Open the GCPs_ground_xyz file in Windows Explorer and tell me what might be wrong with this dataset in terms of how the fields are labeled.XYZ needs to be YXZ.What is the coordinate location provided on the bottom of the screen?43.4833745E 90.4739198SWWhere are the points located? Why?In Antarctica, because the XY coordinate system is flipped in ArcGIS Pro, so X-coordinate is longitude, and the Y-coordinate is latitude.
Control 0 Z = 280.1Control 1 Z = 246.7Control 2 Z = 243.69Control 3 Z = 241.37Control 4 Z = 247.98Control 5 Z = 271.96Control 6 Z = 280.58Control 7 Z = 270.51Control 8 Z = 266.98Control 9 Z = 249.04Flag 3 Z = 263.61Northernmost point: 280.58 - control 6Southernmost point: 241.37 - control 3What are those values? What is the difference between the survey value and the elevation value? What do you suppose is going on?Northernmost point: 312.33 m ... difference = 31.75 mSouthernmost point: 273.13 m ... difference = 31.76 mHow do you plot geodetic marks on the map?Press on a spot and right-click click and press add markerWrite down the information for that marker when you click on it.It gave me the GEOID height, which was the difference between the Ellipsoid Ht. and the Ortho Ht. In addition, it provided the model used, the orthomosaic height, location, network accuracy, and more.What is the difference between the Ellipsoid Ht. and the Ortho Ht? How does that relate to the difference you noted?The difference between the Ellipsoid height and the orthomosaic height is 33.852 meters. This is slightly more than the difference that I calculated, which was around 32 meters; however, it is relatively close.
272.77 m849.9 ftGEOID12A33.852 m33.853 mThese values are 33.852 meters more than the elevation values given to us. Refer to Figure X. 
Geographic Datums
Introduction
Geographical datums provide the foundational reference framework used to define precise locations on Earth’s surface. This makes them vital for all modern mapping and geospatial analysis. Datums help verify that latitude, longitude, and elevation measures are consistent and comparable. In this lab, I explored the fundamental concepts behind geographic datums, recognized and compared different types of datums, learned to identify the quality and issues in a vertical datum, and learned how to utilize XYZ and YXZ coordinate data in software such as ArcGIS Pro and ArcGIS Earth.
Objectives
1. Objective #1: Discover, identify, and apply basic concepts behind geographic datums.
2. Objective #2: Recognize, relate, and compare different types of datums in ArcPro.
3. Objective #3: Demonstrate proficiency and knowledge on how to effectively bring XYZ coordinate data into both ArcGIS Pro and ArcGIS Earth.
4. Demonstrate proficiency and knowledge on how to effectively determine the quality of a dataset and identify issues with the vertical datum.
Resources Used
Steps Taken
To complete the objectives for this lab, I was provided with a “less-than-ideal file to see how improper use of datums can ruin UAS datasets. The file included an improper Ground Control Point file, and I learned what not to do and how to correct it. Upon reviewing this data file, it became clear that there was a lack of metadata, and it was unclear what I was actually looking at.
The first step I took was opening ArcGIS Pro and importing this data folder. After, I imported a .txt version of the file. Right away, I could see the main issue in this data. Normally, the X-coordinate refers to the latitude axis, and the Y-coordinate refers to the longitudinal axis. However, when working with geographic datums, it is critical to remember that the X-coordinate is the longitudinal axis, and the Y-coordinate is the latitude axis. After I processed this file, I could confirm that the coordinates were flipped due to the result being a blank white map.
Next, I imported another .txt file, this time referring to YXZ rather than XYZ. This file has the longitudinal and latitude position correct. When I processed this file, the result gave the GCPs’ coordinates on the map, Figure 1. However, there was still an issue with the Z value, which refers to the elevation.
Figure 1. YXZ Values
To fully see the issue with the elevation value, I used the ArcGIS Earth software. In ArcGIS Earth, I uploaded the data file containing the YXZ coordinates. This software allowed me to view the GCPs but also visualize the terrain, relief, and view the elevation difference in the terrain. To test the Z value, I looked at the GCP point from the data file and compared it to the elevation value of an area near it. There was a difference in these values. It can be concluded that this was a datum issue. Datums are reference points used for measuring height, and different datums use different geodetic models. This can result in offset and elevation differences.
To confirm the elevation difference, I used the National Geodetic Survey (NGS) Data Explorer. I knew that the data files were from Western Wisconsin in an area close to Bloom City. In the NGS map, I looked up Bloom City and used geographic markers, like rivers and roads, to locate the correct marker, as shown in Figure 2. After confirming the correct data marker, it gave a datasheet, Figure 3.
Figure 2. Bloom City Marker
Figure 3. NGS Data Sheet
This datasheet contains critical information like the Orthomosaic height, GEOID height, model used, and more. This information is needed when doing precise work with UAS to make it survey-grade. This datasheet reveals the height difference in GEOID12A for our Z values, which was 33.852 meters. After confirming this, I applied the values and corrected the Z value error, as shown in Figure 4.
Figure 4. Correct Z Value
Questions Answered
Click on each marker and write down the Z value of each one in the space below
Click on the Northern most point on the hillslope, and the southern most by the creek. What are their elevation values?
Look over the datasheet and answer the questions below:
1. What is the NAVD 88 Ortho Height
2. What is the NAVD 88 Ortho Height in Feet?
3. Which Geoid Model was used to calculate the NAVD 88 orthometric height?
4. What is the Geoid Height under the Geoid12A?
5. What is the Geoid Height under the Geoid18?
6. Apply the Geoid12A height differences to each of the Z values in your survey points and write down those values below. How do these match up to the elevation values?
Table 19
Control 01
281
Control 02
278
Control 03
275
Control 04
282
Control 05
306
Control 06
314
Control 07
304
Control 08
301
Control 09
283
Control 00
314
Flag 3
297
There are no rows in this table
Figure 5. Geographic Datums in Western Wisconsin
Summary
Geographic datums are crucial in the UAS industry as they provide a standard, consistent, and accurate reference for locations on Earth. This allows for the spatial data from drone imagery to be correctly aligned, analyzed, and processed. Without datums, data from different sources would be misaligned, which would lead to significant errors. In this lab, I learned and applied the basic concepts behind geographic datums, compared different datum types, demonstrated proficiency in using XYZ and YXZ coordinates in online software, and effectively determined the quality of a dataset and identified issues with the vertical datum.
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