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diff --git a/nz_linz/README.nz_linz b/nz_linz/README.nz_linz index f35df84..b3d7c4e 100644 --- a/nz_linz/README.nz_linz +++ b/nz_linz/README.nz_linz @@ -1,17 +1,145 @@ # README.nz_linz The files in this section result from the conversion of datasets originating -from [LINZ](https://www.linz.govt.nz) +from [Land Information New Zealand] + +The New Zealand grids are +required for coordinate transformations between New Zealand geographic +and vertical coordinate systems. + +The New Zealand grids are sourced from [Land Information New Zealand] +and are also available from LINZ as a separate resource [proj-datumgrid-nz]. + +The New Zealand grids are published under the +[Creative Commons Attribution 4.0 International licence]. ## Included grids -### New Zealand: NZGD49 -> NZGD2000 +### NZGD1949 to NZGD2000 transformation + +*Filename*: nzgd2kgrid0005.tif +*Reference*: https://www.linz.govt.nz/data/geodetic-system/coordinate-conversion/geodetic-datum-conversions/nzgd1949-nzgd2000 + +Distortion grid to convert New Zealand Geodetic Datum 1949 longitude and latitude +to New Zealand Geodetic Datum 2000 longitude and latitude. + +#### Usage + +Conversion from NZGD1949 to NZGD2000 using proj strings + + echo '173 -41 0' | cs2cs -v -f %.8f +proj=longlat +ellps=intl +datum=nzgd49 +nadgrids=nzgd2kgrid0005.tif +to +proj=longlat +ellps=GRS80 +towgs84=0,0,0 + +Conversion from NZGD1949 to NZGD2000 using EPSG codes. Note that this uses +EPSG specified coordinate order for coordinate systems (latitude/longitude in this case). + + echo '-41 173 0' | cs2cs -f %.8f EPSG:4272 EPSG:4167 + +### Quasigeoid grids + +Two geoid grid files are included: + +*Geoid*: New Zealand Quasigeoid 2009 +*Filename*: nzgeoid2009.tif +*Reference*: https://www.linz.govt.nz/data/geodetic-system/datums-projections-and-heights/vertical-datums/new-zealand-quasigeoid-2009-nzgeoid2009 + +*Geoid*: New Zealand Quasigeoid 2016 +*Filename*: nzgeoid2016.tif +*Reference*: https://www.linz.govt.nz/data/geodetic-system/datums-projections-and-heights/vertical-datums/new-zealand-quasigeoid-2016-nzgeoid2016 + +These grids define the height of the New Zealand Quasigeoid relative to the ellipsoidal +height surface on which NZGD2000 is based (nominally a GRS80 ellipsoid aligned ITRF96 +at epoch 2000.0). See https://www.linz.govt.nz/nzgd2000 for more information on the +NZGD2000 datum. +The current NZGD2000 deformation model has this as the zero elevation of NZGD2000 +coordinates at the current epoch. + +These quasigeoids are the reference surfaces the New Zealand Vertical Datum 2009 +(NZVD2009) and New Zealand Vertical Datum 2016 (NZVD2016). + +#### Usage + +To convert a NZGD2000 ellipsoidal height 100.0 to a NZVD2016 orthometric height at 173W 41S + + echo '173 -41 100.0' | cs2cs -v -f %.8f +proj=longlat +ellps=GRS80 +to +proj=longlat +ellps=GRS80 +geoidgrids=nzgeoid2016.tif + +To convert a NZVD2016 orthometric height to a NZGD2000 ellipsoidal height + + echo '173 -41 100.0' | cs2cs -v -f %.8f +proj=longlat +ellps=GRS80 +geoidgrids=nzgeoid2016.tif +to +proj=longlat +ellps=GRS80 + +To convert a NZGD2000 ellipsoidal height 100.0 to a NZVD2016 height at 173W 41S using EPSG codes (requires proj > 6.2) + + echo '-41 173 100.0' | cs2cs -f %.8f EPSG:4167 EPSG:4167+7839 + + +### Local vertical datum transformation grids + +Thirteen grids are provided to transform heights between NZVD2016 and +the [New Zealand local vertical datums]. + +These grids represent the systematic errors in the local vertical datums. +The local vertical datums are each based on levelling from a tide gauge. +They include systematic errors from the levelling as well as a potential of the local +tidal signal at the port from the global mean gravitational equipotential surface. The +NZVD2016 datum is based on gravity measurements from a national airborne gravity +program and is much less prone to regional systematic errors. The transformation grids +are derived from comparing the benchmark heights at which both levelling data and GNSS +(Global Navigation Satellite system) data are available. + +The height determined from the grid model is added to an NZVD2016 height to obtain +the corresponding local vertical datum shift. + +The following grids are available: + +*Local vertical datum*: Auckland 1946 +*Filename*: auckht1946-nzvd2016.tif + +*Local vertical datum*: Bluff 1955 +*Filename*: blufht1955-nzvd2016.tif + +*Local vertical datum*: Dunedin 1958 +*Filename*: duneht1958-nzvd2016.tif + +*Local vertical datum*: Dunedin-Bluff 1960 +*Filename*: dublht1960-nzvd2016.tif + +*Local vertical datum*: Gisborne 1926 +*Filename*: gisbht1926-nzvd2016.tif + +*Local vertical datum*: Lyttelton 1937 +*Filename*: lyttht1937-nzvd2016.tif + +*Local vertical datum*: Moturiki 1953 +*Filename*: motuht1953-nzvd2016.tif + +*Local vertical datum*: Napier 1962 +*Filename*: napiht1962-nzvd2016.tif + +*Local vertical datum*: Nelson 1955 +*Filename*: nelsht1955-nzvd2016.tif + +*Local vertical datum*: One Tree Point 1964 +*Filename*: ontpht1964-nzvd2016.tif + +*Local vertical datum*: Stewart Island 1977 +*Filename*: stisht1977-nzvd2016.tif + +*Local vertical datum*: Taranaki 1970 +*Filename*: taraht1970-nzvd2016.tif + +*Local vertical datum*: Wellington 1953 +*Filename*: wellht1953-nzvd2016.tif + +#### Usage + +To convert from a local vertical datum height to a NZVD2016 height. + + echo '175 -37 0' | cct +proj=vgridshift +inv +grids=auckht1946-nzvd2016.tif +multiplier=1 -*Source*: [LINZ](https://www.linz.govt.nz/data/geodetic-system/download-geodetic-software/gd2000it-download) -*Format*: GeoTIFF converted from NTv2 -*License*: [Creative Commons Attribution 3.0 New Zealand](https://creativecommons.org/licenses/by/3.0/nz/) +To convert from a NZVD2016 height to a local vertical datum height. -This grid file was computed by Land Information New Zealand at approximately -a 20 km interval for the conversion between NZGD49 and NZGD2000. + echo '175 -37 0' | cct +proj=vgridshift +grids=auckht1946-nzvd2016.tif +multiplier=1 -* nzgd2kgrid0005.tif +[Land Information New Zealand]: https://www.linz.govt.nz +[proj-datumgrid-nz]: https://www.geodesy.linz.govt.nz/download/proj-datumgrid-nz +[New Zealand local vertical datums]: https://www.linz.govt.nz/data/geodetic-system/datums-projections-and-heights/vertical-datums/vertical-datum-relationship-grids +[Creative Commons Attribution 4.0 International licence]: https://data.linz.govt.nz/license/attribution-4-0-international/ |