Then you want the datum transformation equations/algorithms? One place is the EPSG aka OGP Geomatics Committee Guidance Note 7-2. This particular transformation uses a "3 parameter" transformation, geocentric translation. Many of the equation-based methods work in 3D Cartesian (XYZ) coordinates so you will have to implement lat/lon/h to/from XYZ converters too.
The macro is esriSRGeoTransformation_NAD1983_To_WGS1984_1 but you can always use the well-known ID instead, 1188. You would use it to create a geotransformation that would then be used with the ProjectEx or ProjectEx5 methods.
Melita: Actually, I need to the calculation formula or component for this conversion for dynamically converting some individual points. Do you have any idea how to get it? Thanks.
Then you want the datum transformation equations/algorithms? One place is the EPSG aka OGP Geomatics Committee Guidance Note 7-2. This particular transformation uses a "3 parameter" transformation, geocentric translation. Many of the equation-based methods work in 3D Cartesian (XYZ) coordinates so you will have to implement lat/lon/h to/from XYZ converters too.
