# Changes between Version 9 and Version 10 of Procedures/AlsprocProcessing

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Timestamp:
Sep 27, 2013 10:29:23 AM (6 years ago)
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• ## Procedures/AlsprocProcessing

 v9 [[Image(pitch_error_corrected_249-2012.jpg, align=center)]] Determine the direction of your error. You need to decide whether to add or subtract from each of the pitch and roll error. Look at the times of a few points in each flightline to determine each of their directions, and then decide whether you want to roll the angle of the laser clockwise or anticlockwise around the direction of travel of the plane to move the data left or right respectively; and whether you want to pitch up or down to move the data forwards or backwards respectively. Determine the direction of your error. You need to decide whether to add or subtract from each of the pitch and roll error in the fields `pitch-correct` and `roll-correct` respectively. Look at the times of a few points in each flightline to determine each of their directions, and then decide whether you want to roll the angle of the laser clockwise or anticlockwise around the direction of travel of the plane to move the data left or right respectively; and whether you want to pitch up or down to move the data forwards or backwards respectively. The table below indicates the effects of addition of subtraction on each axis. || '''Operation''' || '''Pitch''' || '''Roll''' || || addition        || ? || ? || || subtraction     || ? || ? || || addition        || backwards   || left      || || subtraction     || forwards    || right      || You may estimate the magnitude of your adjustment yourself based on your own intuition or previous observations if you wish. Using an equation can help you zero in on the correct solution more quickly, especially in your first two or so observations. e = arctan( d / (h1 + h2) ) Where: e will be your error to add to or subtract from the value used to compute this dataset, d is the difference you measured in lag, h1 and h2 are the heights of the plane in each flightline above the terrain at the time of the observation. Where: e will be your error to add to or subtract from the value used to compute this dataset, d is the difference you measured in lag, h1 and h2 are the heights of the plane in each flightline above the terrain at the time of the observation. (Make sure you convert everything to the same units of measurement, such as metres.) Now return to processing the dataset, you can inspect the data and pass it off, or you can perform another iteration to get the match even closer. The number of iterations you will need to do can vary, but often depends on the quality of the navigation data.