Datums

 Introduction

Within this lab, we were taught the importance of data collection and to ensure that the data that is collected is right. The first and most important thing is the metadata of the flight, this contains flight-critical data such as the time of the flight and what aircraft did the flight. The next most important thing is that the GPS data that is gathered is in the right format, as reversing latitude and longitudinal numbers can give one drastically different locations on Earth. 

Ground Control Points

Before a flight Ground control points (GCPs) are place around the area. These give accurate position data to the aircraft and allow for fixed points where the data was gathered. The coordinates are given in an XYZ style that the computer then can use to place the point precisely in space. X is longitude, this makes sense as the X-axis on a graph goes in the same direction as longitude lines, Y is the latitude and again follows the same reasoning. Z is the vertical distance.

Ellipsoid vs Ortho

There are two different types of height measurements within aviation. These come about due to the fact that the Earth is not a perfect sphere and there are different ways to measure the height of the aircraft. If you ask a pilot what are the two measurements they would say mean sea level (MSL) and above ground level (AGL) this corresponds to the ellipsoid and ortho measurements, but it is important to get them right as flipping them might cause an accident or poor data collection as a result. Ellipsoid height is the difference between the actual earth surface and the ellipsoid thus its AGL, while ortho is the height compared to average sea level (MSL). Figure 1 shows an image of how ellipsoid and ortho heights are taken.

Figure 1: Ellipsoid vs Ortho

Conclusion

Datums are very important when it comes to gathering data. When you have to gather location points and determine the altitude it is important that you use the right measurement. By using ArcGIS to process your data you can see if there are any issues with the data. In completion of this lab it was obvious that it is important to take down the data and in the right way, as if we didnt have the proper GCPs within the lab all the data would have been trashed.