CueTip – Transforming WGS 84 (G1150) Coordinates to NAD 83 (CORS96) Coordinates

Datums identified only as NAD 83 or WGS 84 are not specific enough to clearly define the reference frame of geodetic data. Additional information is needed that defines the realization or version of a particular datum. In the case of NAD 83, a “datum tag” must be appended to the name, such as NAD 83 (86) or NAD 83 (CORS96); likewise for WGS 84: WGS 84 (G1150), WGS 84(original), etc. NAD 83 (CORS96) and WGS 84 (G1150) are the current versions of these systems. While NAD 83 (86) and WGS 84 (original) were equivalent datums, this is not the case for CORS96 and G1150. A datum transform is required when transforming points between any projected or geographic coordinate systems based on these datums. For these particular datums, the magnitude of the difference is on the order of two meters.

Clearly then, the first step is to know precisely the datum to which your input data is referenced. If your processing will require that this data be transformed to another coordinate system which is not based on the same datum, then you must consider the required datum transform. This note will consider the common case in which input data is referenced to WGS 84 (G1150) and requires being converted to a coordinate system based on NAD 83 (COR96), as these are the current versions of those datums. It is important to note here that for these particular datums, it will also be required to know the date to which the GPS data is processed, also known as the epoch of the data. The will be explained further below.

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