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Diffstat (limited to 'docs/source')
| -rw-r--r-- | docs/source/operations/transformations/index.rst | 1 | ||||
| -rw-r--r-- | docs/source/operations/transformations/xyzgridshift.rst | 91 | ||||
| -rw-r--r-- | docs/source/references.bib | 9 |
3 files changed, 101 insertions, 0 deletions
diff --git a/docs/source/operations/transformations/index.rst b/docs/source/operations/transformations/index.rst index d4bbf4e0..6bd503d4 100644 --- a/docs/source/operations/transformations/index.rst +++ b/docs/source/operations/transformations/index.rst @@ -19,3 +19,4 @@ systems are based on different datums. molobadekas hgridshift vgridshift + xyzgridshift diff --git a/docs/source/operations/transformations/xyzgridshift.rst b/docs/source/operations/transformations/xyzgridshift.rst new file mode 100644 index 00000000..c49b7592 --- /dev/null +++ b/docs/source/operations/transformations/xyzgridshift.rst @@ -0,0 +1,91 @@ +.. _xyzgridshift: + +================================================================================ +Geocentric grid shift +================================================================================ + +.. versionadded:: 7.0.0 + +Geocentric translation using a grid shift + ++-----------------+-------------------------------------------------------------------+ +| **Domain** | 3D | ++-----------------+-------------------------------------------------------------------+ +| **Input type** | Cartesian coordinates | ++-----------------+-------------------------------------------------------------------+ +| **Output type** | Cartesian coordinates | ++-----------------+-------------------------------------------------------------------+ + +Perform a geocentric translation by bilinear interpolation of dx, dy, dz +translation values from a grid. The grid is referenced against either the +2D geographic CRS corresponding to the input (or sometimes output) CRS. + +This method is described (in French) in :cite:`NTF_88` +and as EPSG operation methode code 9655 in :cite:`IOGP2018` (ยง2.4.4.1.1 +France geocentric interpolation). + +The translation in the grids are added to the input coordinates in the forward direction, +and subtracted in the reverse direction. +By default (if grid_ref=input_crs), in the forward direction, the input coordinates +are converted to their geographic equivalent to directly read and interpolate from +the grid. In the reverse direction, an iterative method is used to be able to find +the grid locations to read. +If grid_ref=output_crs is used, then the reverse strategy is applied: iterative +method in the forward direction, and direct read in the reverse direction. + +Example +------------------------------------------------------------------------------- + +NTF to RGF93 transformation using gr3df97a.tif grid + +:: + + +proj=pipeline + +step +proj=push +v_3 + +step +proj=cart +ellps=clrk80ign + +step +proj=xyzgridshift +grids=gr3df97a.tif +grid_ref=output_crs +ellps=GRS80 + +step +proj=cart +ellps=GRS80 +inv + +step +proj=pop +v_3 + +Parameters +################################################################################ + +The ellipsoid parameters should be the ones consistent with ``grid_ref``. +They are used to perform a geocentric to geographic conversion to find the +translation parameters. + + +Required ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ + +.. include:: ../options/ellps.rst + +.. option:: +grids=<list> + + Comma-separated list of grids to load. If a grid is prefixed by an `@` the + grid is considered optional and PROJ will the not complain if the grid is + not available. + + Grids are expected to be in GeoTIFF format. If no metadata is provided, + the first, second and third samples are assumed to be the geocentric + translation along X, Y and Z axis respectively, in metres. + +Optional ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ + +.. option:: +grid_ref=input_crs/output_crs + + Specify in which CRS the grid is referenced to. The default value is + input_crs. That is the grid is referenced in the geographic CRS corresponding + to the input geocentric CRS. + + If output_crs is specified, the grid is referenced in the geographic CRS corresponding + to the output geocentric CRS. This is for example the case for the French + gr3df97a.tif grid converting from NTF to RGF93, but referenced against RGF93. + Thus in the forward direction (NTF->RGF93), an iterative method is used to find + the appropriate shift. + +.. option:: +multiplier=<value> + + Specify the multiplier to apply to the grid values. Defaults to 1.0 + diff --git a/docs/source/references.bib b/docs/source/references.bib index 0668e10d..8e527ea1 100644 --- a/docs/source/references.bib +++ b/docs/source/references.bib @@ -230,6 +230,15 @@ Doi = {10.2312/PE/PG/PG2012short/005-010} } +@TechReport{NTF_88, + Title = {Grille de parametres de transformation de coordonnees - GR3DF97A - Notice d'utilisation}, + Author = {IGN}, + Institution = {Service de Geodesie et Nivellement, Institut Geographique National}, + Year = {1997}, + + Url = {https://geodesie.ign.fr/contenu/fichiers/documentation/algorithmes/notice/NTG_88.pdf} +} + @TechReport{ONeilLaubscher1976, Title = {Extended Studies of a Quadrilateralized Spherical Cube Earth Data Base}, Author = {E. M. O'Neill and R. E. Laubscher}, |