I need your advice on the "one step transformation" process for creating ground coordinates from grid coordinates
Our project area is a 260 km long proposed railway line corridor. The proposed railway corridor needs to be designed after doing the detailed topographical survey
The first step followed is : Established 85 pairs of control points (say GPS1 to GPS 85) along the corridor using DGPS.
Second step: Convert the control point LLH (Lat,Lon,Ht) to grid coordinates (XYZ) based on UTM projection system
Third step: Convert grid coordinates to Local coordinates using one step transformation with the method - One point localization. Here the localization base is one of the GPS stations (say GPS 83). During one point localization the ground coordinates (i.e Position & Height (P&H)) of all control points are derived w.r.t GPS 83 . Here the paramters for one point localization such as Flase easting,False Northing etc are set using UTM easting and northing of GPS83.
My question :
1. For a linear project of 260 km long, is it a right approach to create ground coordinates of all DGPS control points w.r.t to GPS 83 (which is at one end of the corridor)
2. Second question is, should multiple DGPS control points (use their UTM grid coordinates) be used for localization which may be spread out in the 260km long corridor
3. What are the advantages of using one point localization and what are its disadvantages (considering the fact that we need to re convert the ground coordinates back to true UTM coordinates).
The proposed alignment is designed on ground coordinates, and the design team is creating railway corridor centerline, right and left corridor points based on ground coordinates.
KML when created using ground coordinates (assuming they are UTM) cannot be used for visualization in google earth since they don't fall at the right location.
The final location survey : Where the corridor pillars are pegged on the ground using Total station are w.r.t to ground coordinates.
The problem I am facing is : the land mapping is done using UTM coordinates (geo-referencing of cadastral maps is done using DGPS coordinates / UTM coordinates), and we need a solution for the problem so that land acquisition proposed using the cadastral maps matches the final location survey.