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Revision as of 10:30, 21 March 2016 by Singhdj2
1.2. Field Setup ❏ Early in the crop season, distribute at least 10-15 ground control points (GCP) uniformly throughout the field. Four GCPs fixed in the field corners and rest distributed inside the field, preferably, in the alley ways for better visibility. Survey the GCPs with either RTK or a DGPS GNSS systems (whichever available) multiple times during the season to reduce the day/time bias. Make sure the GCPs are not disturbed/moved from their fixed positions once surveyed throughout the crop season. Generally, the white color GCPs are easy to spot, hence, should be preferred. Some photogrammetry softwares support automatic GCP detection. When available, these software customized GCPs can also be used. Here are a few examples of GCPs that have worked well for us: i. Metal sheets screwed on top of the iron rods (example)File:Example.jpg. ii. Color brick/pavers (example)File:Example.jpg iii. Plastic discs/frisbees ❏ Place the reference calibration panel on a flat surface close to the first mission waypoint at a fixed position (Figure 1.1) Note: The panel can also be utilized as a launchpad expecially when it is wide. Also, in order to minimize the variations due to varying sun illumination and overcast, maximum aerial shots of calibration panel at regular intervals are recommended. This can be achieved either by using multiple calibration targets or by capturing images of a target at every landing and takeoff event during the mission. A 20% gradient grayscale calibration panel can be used as a reference panel. The details to build a calibration panel are described in this document. ❏ Mark the four corners of calibration panel with flags and survey them with RTK or DGPS GNSS system. Fixed panel positions make the automatic extraction of individual color panels easier during the post-processing. Figure 1.1: Example of a grayscale calibration panel attached on a metal frame.