SURDIFY Output
The surdify program operates on output from the icess program. The icess program smooths
blocks of qfit output on each side of the aircraft. Typically, blocks about 75m square are
fitted to a plane, with a center elevation and two slopes estimated. Such a block has been
termed a platelet by Bob Thomas and this convention will be adopted. The surdify program
computes differences by comparing a platelet from a test trajectory with the closest platelet
from a reference trajectory. The platelet used from the reference trajectory is actually an
interpolation of the two closest platelets, although only interpolations of platelets from the
same side of the aircraft are allowed. The height differences computed are for the midpoint
between the test platelet and the interpolated reference platelet. The following are the entries
on each record of the surdify output:
1. The date of the test platelet.
2. The test platelet time in seconds of the day.
3. The date of the reference platelet.
4. The reference platelet time in seconds of the day.
5. The latitude at the comparison point in degrees.
6. The longitude at the comparison point in degrees.
7. The elevation at the comparison point, based on the test platelet in meters.
8. The rate of change of the elevation at the comparison point in m/yr.
9. The slope difference between the platelets in the alongtrack (pitch) direction in deg.
10. The slope difference between the platelets in the crosstrack (roll) direction in deg.
11. The distance of the comparison point from the first point on the original icess output
file.
12. The minimum distance between the test platelet and a reference platelet.
13. The distance between the test platelet and the interpolated reference platelet. This
distance is signed, with a positive distance indicating that the reference platelet is on
the starboard side of the test platelet and a negative sign indicating the port side.
14. The height difference between platelets at the center of the test platelet.
15. The height difference between platelets at the center of the reference platelet.
16. The partial derivative with respect to velocity of the height change in the north-south
direction, with units of seconds.
17. The partial derivative with respect to velocity of the height change in the east-west
direction, with units of seconds.
18. The offset of the test platelet from the aircraft trajectory in meters, signed as for
output 13.
19. The offset of the reference platelet from the aircraft trajectory in meters, signed as for
18.
20. The rms of fit of the test platelet, in cm.
21. The rms of fit of the reference platelet, in cm.