Overview

Keograms are very useful to show the sky conditions of a full night in a single image.

A keogram is generated by rotating every image, extracting a single column of pixels from the center of the rotated image, and adding the column of pixels sequentially to a new image.

Rotation

The image rotation angle need to approximately match the angle of meridian in your all sky camera.

A rotation of 0 degrees means no rotation is performed. A positive rotation (1 to 180) will rotate the image counter clockwise [CCW]. A negative rotation (-1 to -180) will rotate the image clockwise [CW].

Using the following image as an example.

Applying a rotation of -45 degrees will rotate the image 45 degrees CW.

Example

This is the approximate location of the meridian in the image above. There are two valid rotation settings:

• [+]35 to 45 degrees for a CCW rotation
• -125 to -135 degrees for a CW rotation if you wish to invert the keogram orientation