Skyline Heading is the true direction that the SunEye was pointing when the measurement was taken. Actually, more accurately, it is the direction the SunEye THINKS it was pointing when the measurement was taken. It is therefore the top of the fisheye chart, ?twelve o?clock? on the Annual Sunpath view. In the case of the SunEye 110, it is south (180 degrees) offset by the magnetic declination. (The SunEye 110 always assumes it is facing magnetic south). For the SunEye 210, it is more complicated. For older versions, Version 4.50 or earlier, the heading is always 180 degrees, since the SunEye 210 version 4.50 or earlier always assumes it is facing true south.   With Version 4.55 and later, the SunEye 210 provides auto-correction within a wide range of azimuths. The heading could be anything 180 degrees plus or minus 30 degrees (recommended window, but actually any azimuth will get corrected), and the SunEye will automatically correct for it. Note that the image may appear rotated, and the SunEye does NOT correct the image to reverse the rotation. It just displays the heading so that you know what is the azimuth on the top of the Annual Sunpath view.   So how does it affect TSRF and Solar Access calculations? It does not. In the case of the 110 or 210 4.50 or earlier, the heading is fixed by the SunEye algorithms. In the case of 210 Version 4.55 or later, the heading is adjusted based on the compass reading. At times the image can get rotated, and look a bit distorted on the autoscaled version that is displayed. But in any case, the TSRF and Solar Access calculations are not affected. The calculations are based only on the image taken assuming that the compass is correct. Heading is only displayed to assist with interpretation of the image.   For extra completeness, the behavior of the SunEye 210 in ?Target mode? should also be described. (Version 4.30 or later). Recall that target mode is for when you assume that the compass is not working due to interference, and therefore you override it with the target, that is a known azimuth, not necessarily south. So in Target mode the SunEye will display a heading equal to what you entered for the target, and it will NOT autocorrect for the compass, since the compass will be ignored.  

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