One of the metrics that canopy pilots have been using to evaluate their swoops is the time it takes to transition from vertical flight to horizontal flight (the rollout phase). This can be measured with a video camera but there are advantages to using GPS:
1) ease of use - A video camera requires you to use a stopwatch or to manually step through frames. Your GPS can measure the rollout automatically.
2) accuracy - Determining the start and end of the rollout is not as trivial as it might seem. Using a camera you would typically wait until the canopy is on final heading before starting the stopwatch. But the rollout sometimes starts before that. With GPS you can look at vertical deceleration to more reliably detect the start of the rollout.
3) repeatability - Using a camera there are several sources of human error when measuring the rollout time. With GPS you can use a well defined algorithm that makes comparisons more meaningful.
Starting with gSwoop 2.10 (released yesterday) there have been improvements to the algorithm used to detect the start and end of the rollout. The start is defined as the point where vertical speed begins to monotonically decrease (which occurs near the time of your final snap). The end is defined as 1 meter above where level flight is achieved. The 1 meter offset is necessary to isolate the rollout from the slightly sinking phase that can go on for quite some time even after successfully scoring the entry gate. It is a somewhat arbitrary offset but when applied consistently it is possible to make meaningful comparisons between swoops.
Here is an example from my first round of speed at Nationals this year:
exited airplane: 6396 ft AGL
initiated turn: 1600 ft AGL, 810 ft back, -382 ft offset
max vertical speed: 383 ft AGL, 264 ft back, 192 ft offset (96.3 mph)
started rollout: 315 ft AGL, 270 ft back, 179 ft offset (91.7 mph)
finished rollout: 13 ft AGL, 40 ft back, 23 ft offset
max total speed: 723 ft AGL, 297 ft back, 116 ft offset (100.4 mph)
max horizontal speed: 30 ft AGL, 101 ft back, 44 ft offset (80.2 mph)
degrees of rotation: 652 deg (right-hand)
time to execute turn: 13.90 sec
time during rollout: 3.35 sec
time aloft during swoop: 7.65 sec
entry gate speed: 73.7 mph
distance to stop: 270 ft
touchdown estimate: 270 ft (2.0 mph)
speed carve time: 2.56 sec (47.8 mph)
During this run I started my rollout at 315 feet AGL and it took 3.35 seconds to complete. I was 270 feet behind the gate at the start of the rollout (324 feet away when you consider the offset) and 40 feet back at the finish. You can see a video of this run here (thanks to Keith Creedy for the footage):
https://www.dropbox.com/sh/ecqp7ywqqa9ve2d/AAAxrlUUavJIN7mw6udaC4tKa/Speed%20Round%201/Speed_Rd_1_Shot16_kc.mp4?dl=0