I have gone through and added the library to my .NET project and it is magnificent!!! It has all the functions that I desperately needed. Thank you so much.
One thing I am looking to do is to create range rings. In other words from an origin point how far would an aircraft be able to travel as a radius. The outer perimeter would construct a geoellispe. Would I just cycle through a number of azimuths and use the origin point, the azimuth, and the distance to get each and every point on the perimeter?
My only concern on that is that depending on the area of the globe a certain angle will give me a certain arc length but in another area it might give me a different arc length. Is there a possibility to create a geoellipse such that the perimeter is made up of points say every 100KM?
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Because the earth is nearly spherical, generating your range rings by
computing a set of destinations with a constant s12 and equally spaced azi1 will result in points which are very nearly equally spaced. (By
the way, I don't understand why you refer to this as a "geoellipse". I
would have thought the normal terminology would be "geodesic circle".)
If you want to delve deeper then the actual spacing of the end points is
approximated by m12dazi1 where m12 is the reduced length and dazi1 is
the change in azi1 (in radians). For a sphere m12 = a sin(s12/a)
where a is the radius of the sphere. This result is slightly altered
for an ellipsoid and is returned as an optional result by the geodesic
routines.
Last edit: Charles Karney 2017-05-05
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rrently what I do is estimate the perimeter by C = 2piR. So with a radius in meters I can get the perimeter length in meters. Once I have that then I divide by the MaxArcLength to get number of slices I need. So then I just do a For az = 0 To 360 Step N and generate an outer point. Connecting the outer points gives me the vertices of my polygon (range ring). Let me try your approach to see how that affects the process. In this case, this step only provides the number of slices I need to make to get a max distance between each perimeter point. As the radius gets bigger, the number of slices needed to get that max arc distance will also increase.
I have heard these types of polygons called range rings, geodesic circles, and geoeliipses. The latter comes from using ArcGIS where they state:
IGeoEllipse Interface
Description
A GeoEllipse is a spheroidal ellipse whose geometry is defined by a center point, X/Y axes, and a spatial reference. The spatial reference provides the spheroid for the GeoEllipse calculation. The GeoEllipse object can be used to provide the geometry of the GeoEllipseElement for display as a graphic element.
Last edit: AGP 2017-05-05
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
I have gone through and added the library to my .NET project and it is magnificent!!! It has all the functions that I desperately needed. Thank you so much.
One thing I am looking to do is to create range rings. In other words from an origin point how far would an aircraft be able to travel as a radius. The outer perimeter would construct a geoellispe. Would I just cycle through a number of azimuths and use the origin point, the azimuth, and the distance to get each and every point on the perimeter?
My only concern on that is that depending on the area of the globe a certain angle will give me a certain arc length but in another area it might give me a different arc length. Is there a possibility to create a geoellipse such that the perimeter is made up of points say every 100KM?
Because the earth is nearly spherical, generating your range rings by
computing a set of destinations with a constant s12 and equally spaced
azi1 will result in points which are very nearly equally spaced. (By
the way, I don't understand why you refer to this as a "geoellipse". I
would have thought the normal terminology would be "geodesic circle".)
If you want to delve deeper then the actual spacing of the end points is
approximated by m12 dazi1 where m12 is the reduced length and dazi1 is
the change in azi1 (in radians). For a sphere m12 = a sin(s12/a)
where a is the radius of the sphere. This result is slightly altered
for an ellipsoid and is returned as an optional result by the geodesic
routines.
Last edit: Charles Karney 2017-05-05
rrently what I do is estimate the perimeter by C = 2piR. So with a radius in meters I can get the perimeter length in meters. Once I have that then I divide by the MaxArcLength to get number of slices I need. So then I just do a For az = 0 To 360 Step N and generate an outer point. Connecting the outer points gives me the vertices of my polygon (range ring). Let me try your approach to see how that affects the process. In this case, this step only provides the number of slices I need to make to get a max distance between each perimeter point. As the radius gets bigger, the number of slices needed to get that max arc distance will also increase.
I have heard these types of polygons called range rings, geodesic circles, and geoeliipses. The latter comes from using ArcGIS where they state:
IGeoEllipse Interface
Description
A GeoEllipse is a spheroidal ellipse whose geometry is defined by a center point, X/Y axes, and a spatial reference. The spatial reference provides the spheroid for the GeoEllipse calculation. The GeoEllipse object can be used to provide the geometry of the GeoEllipseElement for display as a graphic element.
Last edit: AGP 2017-05-05