To help understand the 7-parameter transformation (translation + rotation + scaling) that’s involved in going from PRS 92 (ESPG:3123) to WGS84, study the section under the heading towgs84.
Emlid Flow doesn’t support the transformation between PRS92 and WGS84 now, but you can add it with a Custom CS. Please walk through this step-by-step guide from our docs to create it. For PRS92 / Philippines zone 3, you’ll need to choose the GRS80 ellipsoid and add the parameters for transformation and projection. You can find them by these links on epsg.org.
I just wanted to update you that we’ve released the support for PRS92 with the datum conversion from WGS84. Now, you can use PTM projections based on the PRS92 datum.
To use any CS based on PRS92 datum, your base or NTRIP service should be in WGS84. The Helmert (7-parameters) performs the datum conversion.