To convert GPS horizontal velocity field data from the Eurasian reference datum to the Indian reference datum, you would typically use a process called datum transformation or coordinate transformation. This transformation involves converting the coordinates from one reference datum to another based on known parameters and mathematical models.
The specific method and steps for achieving the conversion depend on the available data and resources. Here are a few common methods used in datum transformation:
Seven-Parameter Transformation: This method involves applying a seven-parameter transformation that includes translation, rotation, and scale factors to convert the coordinates between the two reference datums. The parameters are determined through the analysis of control points with known coordinates in both datums. The transformation can be achieved using mathematical formulas or software tools specifically designed for datum transformation.
Grid-Based Transformation: In this method, transformation grids are used to model the differences between the two reference datums. The transformation grids consist of a network of control points with known coordinates in both datums. Interpolation techniques are applied to determine the transformation parameters for the given GPS data points based on the grid values.
Geocentric Datum Transformation: Instead of converting directly from one geographic coordinate system to another, this method involves transforming the coordinates to a common geocentric reference frame and then converting them back to the desired geographic coordinate system. This approach typically involves converting from latitude, longitude, and height to a Cartesian coordinate system (X, Y, Z) centered at the Earth's center, performing the transformation, and then converting back to latitude and longitude in the Indian reference datum.
It's important to note that performing accurate datum transformations requires precise knowledge of the parameters and models used for each reference datum. Geodetic authorities and organizations often provide transformation models, software tools, or online services to facilitate the conversion process. Consulting such resources and following established guidelines for datum transformation is recommended to ensure accurate results.
Additionally, depending on the specific requirements and applications of the GPS data, it may be beneficial to consult with geodesy or geomatics experts who have experience in performing datum transformations for your region or area of interest. They can provide further guidance and assistance tailored to your specific needs.