Skyline

The Skyline module analyses the current image and proposes where the skyline or horizon might be. It does this task by minimizing the variance between two halves of the image to the point that a settled state is achieved. This essentially breaks the image into two parts. As most skies are of very different texture than the ground this is an effective technique of determining the split.

For those RC plane enthusiasts it should be noted that an image in one second may contain a horizon but in the next all ground or all sky. This renders the image division useless unless the Model is provided with several frames from previous "good" horizons. Thus, you should start off with the horizon in view which will allow the model to build up a sampling of what is sky and what is ground. When only sky or only ground is suddenly in view the module will indicate this using situation in the SKYLINE_VIEW variable.

Interface

Instructions

1. Display - you can chose to turn off the horizon and ground/sky indicators by unselecting the checkboxes.

2. Model - specify the number of frames that are used to create the ground/sky model. Note that too many frames will cause the model not to update soon enough if the image content changes drastically, too little and the model might update when only looking at ground or sky. At 30 frames a second 30 would sample about 30 frames but would then also require you to move out of all sky or all ground images in a second before the model updates. Try 120 which would build a model over 4 seconds.

Example

Source	Skyline

Variables

SKYLINE_VIEW - either HORIZON, SKY or GROUND depending on what
  the module determines
SKYLINE_ERROR - the goodness of split between the two image
  halves. Lower is better.
SKYLINE_ANGLE - the horizon's angle.
SKYLINE_BANK - the y coordinate of the horizon line with respect
  to the center height.
SKYLINE_X1
SKYLINE_Y1
SKYLINE_X2
SKYLINE_Y2 - the starting and ending line coordinates as seen on
  the screen.

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