Coordinate System

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(New page: ===Coordinate System=== WWJ uses an [http://en.wikipedia.org/wiki/ECEF ECEF] Cartesian coordinate system. Conversions from geodetic (lat, lon, altitude) to Cartesian are computed in the gl...)
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Revision as of 19:18, 7 January 2008

[edit] Coordinate System

WWJ uses an ECEF Cartesian coordinate system. Conversions from geodetic (lat, lon, altitude) to Cartesian are computed in the globe class (EllipsodialGlobe.geodeticToCartesian(...)), where the conversion is essentially applying an Equirectangular projection (or the reverse in the case of geodeticToCartesian()). WWJ uses WGS84 as a means to establish the center and orientation of the earth.

When performing custom transformations (in a render() method for example), the modelview matrix has been transformed to orient the axises to the center of the earth prior to the render call. It's easier to transform geometry using a local world origin, which is established by calling View.pushReferenceCenter() (the referenceCenter argument is in world coordinates). One must call popReferenceCenter() afterwards. A call to View.get*Matrix returns the same matrix as if I asked the opengl pipeline for it.

In WWJ the earth rotational axes is Y, with positive values in the northern hemisphere. Z points toward lat/lon zero and X toward lat zero, lon 90 east.

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