This is a port of TRANS4D (originally written in Fortran) into C++. TRANS4D can be used to transform coordinates across reference frames and epochs. It can also be used to predict velocities and displacements due to crustal mostion.

This is currently a port of version 0.2.6 of TRANS4D. The C++ port is a volunteer project made freely available to help software engineers to be able to compile HTDP/Trans4d on more devices than can be targeted with Fortran. Before using this for production purposes, please make sure to test coordinates using the original TRANS4D program. At the time of writing, many test cases need to be written to verify the accuracy of the translation of velocity grid, earthquake, and post seismic activity.

The National Geodetic Survey's (NGS) official tool for calculating position transformations and crustal motion is Horizontal Time Dependent Positioning (HTDP). TRANS4D is the evolution of that program, written and maintained by Dr. Richard Snay (NGS, Retired). He continues to improve the resolution of velocity grids and incorporates new models into his software.

As of mid 2020, Trans4d's models are more precise than HTDP with velocity grids containing points with 6 km resolution in CONUS. Trans4d's models also incorporate vertical crustal motion. In conversations with Dr. Snay and several NGS employees maintaining HTDP, the NGS plans to use Trans4d to upgrade the functionality of HTDP.

• Make sure the Data4.2.5A.txt and Data4.2.5B.txt files are in the same directory as the executable

• Include "Trans4d.h"

• Use the trans4d::TransformPosition() method

• See the table below for values to use in the IOPT parameter

  // 1;  "WGS_84(transit)";
  // 10; "Stable NA (ITRF2014-PMM)";
  // 12; "NAD_83(PA11/PACP00)";
  // 13; "NAD_83(MA11/MARP00)";
  // /***iframe[6] = 6 (This was incorrect in all versions of HTDP)***/
  // 5;  "WGS_84(G730)";
  // 8;  "WGS_84(G873)";
  // 11; "WGS_84(G1150)";
  // 15; "WGS_84(G1674)";
  // 15; "WGS_84(G1762)";
  // 17; "Pre-CATRF2022 =Caribbean";
  // 2;  "ITRF88";
  // 3;  "ITRF89";
  // 4;  "ITRF90/PNEOS_90/NEOS_90";
  // 5;  "ITRF91";
  // 6;  "ITRF92";
  // 7;  "ITRF93";
  // 8;  "ITRF94";
  // 8;  "ITRF96";
  // 9;  "ITRF97 or IGS97";
  // 11; "ITRF2000 or IGS00/IGb00";
  // 14; "ITRF2005 or IGS05";
  // 15; "ITRF2008 or IGS08/IGb08";
  // 16; "ITRF2014 or IGS14";
  

  Example code converting from NAD83(2011) epoch 2010.0 to ITRF2014 epoch 2020.0

  double lonDegrees = -105.0001;
  double eht = 1500;
  
  double inDate = 2010.0;
  double outDate = 2020.0;
  
  //todo: make these values constants or enums
  int nad83Opt = 1;
  int itrf2014Opt = 16;
  
  double newLat, newLon, newEht;
  trans4d::TransformPosition(latDegrees, lonDegrees, eht, nad83Opt, itrf2014Opt, inDate, outDate, newLat, newLon, newEht);
  

TRANS4D is originally a Fortran program, so for ease of porting/translating, many aspects of this port will feel like a conglomeration of Fortran and C/C++.

• Fortran arrays are indexed starting at 1, whereas C/C++ arrays are indexed starting at 0. To account for this, all arrays in this port start at 1 so as to minimize chances for regression bugs.

• Use of goto/labels is supported in Fortran and C++, although the use of goto within C/C++ is generally discouraged as a best practice. However, for ease of porting, goto/labels will still be used in a few places.

• Subroutine calls in Fortran are all "pass by reference" so the C++ translation from subroutines to methods will involve passing variables by reference as well.

• Fortran logical units for file i/o are replaced by std::fstream objects.

• Common block data are ported into structs with macros for declaring local reference variables that reference the values in the structs. i.e. DECLARE_COMMON_XXXXXX

• Some char arrays will be replaced by std::string

• All scientific notation literal numeric values in C++ are interepreted as 8 byte doubles.

• UI related code is bein separated into the main sample exe while core functionality is refactored into a shared library (dll in Windows)

• C++ has no implicit variable types. In cases where some variables were arbitrarily prefixed with X or Y to ensure they were doubles, those prefixes have been removed to avoid confusion. For example, the variable LON might be desired as a double, but implicitly be an int due to the following declaration:

  IMPLICIT DOUBLE PRECISION (A-H, O-Z)
  IMPLICIT INTEGER*4 (I-N)
  

• Bluebook format related operations are unsupported at this time.

All of the subroutines are listed here from the original trans4d.f file. Below shows progress on subroutines being ported, as well as what is complete. The In Progress section shows what line number the subroutine is translated up to.

For any inquiries on this software:

• feel free to reach out to me at [email protected]
• Dr. Snay's email is [email protected]
• For inquiries about HTDP, contact the NGS at [email protected]