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Determine the latitude/longitude coordinates of the center point of an H3Index cell
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This operation is performed by function `h3ToGeo`. See the comments in the function source code for more detail.
The conversion is performed as a series of coordinate system conversions described below. See the page <a href="#/documentation/core-library/coordinate-systems">Coordinate Systems used by the **H3 Core Library**</a> for more information on each of these coordinate systems.
* The function `_h3ToFaceIjk` then converts the **H3** index to the appropriate icosahedron face number and normalized *ijk* coordinate's on that face's coordinate system as follows:
* We start by assuming that the cell center point falls on the same icosahedron face as its base cell.
* It is possible that the the cell center point lies on an adjacent face (termed an *overage* in the code), in which case we would need to use a projection centered on that adjacent face instead. We recall that normalized *ijk* coordinates have at most two non-zero components, and that in a face-centered Class II system the sum of those components is a resolution-specific constant value for cells that lie on the edge of that icosahedral face.
We determine whether an overage exists by taking the sum of the *ijk* components, and if there is an overage the positive *ijk* components indicate which adjacent face the cell center lies on. A lookup operation is then performed to find the appropriate rotation and translation to transform the *ijk* coordinates into the adjacent face-centered *ijk* system.
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<img height="300" src="images/triEdge.png" />
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* The face-centered *ijk* coordinates are then converted into corresponding *Hex2d* coordinates using the function `_ijkToHex2d`.
* The function `_hex2dToGeo` takes the *Hex2d* coordinates and scales them into face-centered gnomonic coordinates, and then performs an inverse gnomonic projection to get the latitude/longitude coordinates.
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