The important thing to remember is the second axis parameter points North. The values for each semi axis can change which is the major or minor * Heading North for the second ellipse's semi axis, in meters. * Heading East for the first ellipse's semi axis, in meters. * heading the ellipse's heading, clockwise from North. * minorRadius the ellipse's minor radius, in meters. * majorRadius the ellipse's major radius, in meters. The confusion comes from line #91 and similar parameter designations. Where the heading is still relative to North or 0* NOTE: This uses \src\gov\nasa\worldwind\render\SurfaceEl lipse.java Maybe this will help clarify the code for a SurfaceEllipse and direction. The other choice is to swap the semi-major or semi-minor axes in the argument list in the documentation. I return to my original statement that what I think needs to be done is change the documentation to replace "clockwise from North" with "clockwise from East". Upon reading your statement, I started worrying I was going to have to do some math to figure things out and the semi major (minor) didn't specify half the largest (smallest) distance between points in the ellipse. This is good news since we're not dealing with defining heading relative to semi-major and semi-minor. Combine this with the angles BLUE and GREEN are plotted at, you arrive at the conclusion that swapping the minor and major axes are equivalent to rotating by +/- 90 degrees. This looks like MAGENTA has a heading of 90 degrees less (or more - 180 degree ambiguity) than RED. This fact is not shown explicitly but based on the code and the image, but I believe you can extrapolate to see this is true.įor example, RED shows an ellipse and MAGENTA shows the same ellipse with major and minor axes swapped. What I am seeing from this example is that swapping the semi-major and semi-minor axes is equivalent to subtracting 90 degrees from the heading. Below is code that I used to plot the image below. Lacking more information, I just ran some tests. Let me elaborate to see if we can come to a consensus.īefore continuing, I just want to establish that clockwise from a direction means that the direction represents 0 degrees, a positive heading is rotated 'heading' degrees clockwise from the direction, and a negative heading is rotated 'heading' degrees counterclockwise, where the clock is placed face up on the surface of the Earth. A third way to look at this is if semi-major and semi-minor axes are swapped in the argument order, then semi-major points in the direction of heading interpreted as clockwise from North. Another way to look at it is the semi-minor axis points in the direction of heading interpreted as clockwise from North. I believe the semi-major axis points in the direction of heading if the heading is interpreted as clockwise from East. Based on my experiment detailed below, I do not believe you are correct. Thanks for taking time to respond to this. Surface Ellipse Heading is clockwise from East, not North.
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