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Units of NTv2 accuracy samples ?

Even Rouault edited this page Jun 29, 2020 · 13 revisions
NTv2 filename Producer Min/Mean/Max lat accuracy Unit Confirmed by producer
rdtrans2008/rdtrans2018.gsb Kadaster Netherlands 1e-3 / 1e-3 / 1e-3 Metre Yes
ntv2_0.gsb NRCan Canada 0 / 0.27 / 13 (1st subgrid) Metre Yes
ntf_r93.gsb IGN France 1.6e-4 / 0.035 / 0.065 Second Yes
BWTA2017.gsb LGL Germany 1.6e-5 / 6.3e-5 / 1.4e-4 Second Yes
nzgd2kgrid0005.gsb LINZ New Zealand 5.9e-4 / 0.03 / 0.1 Second Yes
OSTN15_NTv2_OSGBtoETRS.gsb Ordnance Survey Great Britain 1e-6 / 5e-6 / 3e-5 Second Yes
bd72lb72_etrs89lb08.gsb IGN Belgium 0.01 / 0.01 / 0.01 Metre Yes
CHENyx06a.gsb Swisstopo Switzerland 1e-3 / 1e-3 / 1e-3 Second Yes
D73_ETRS89_geo.gsb DGTerritorio Portugal 1.5e-3 / 1.5e-3 / 1.5e-3 Second Yes
GDA94_GDA2020_conformal_and ICSM Australia 1e-7 / 7e-4 / 3e-2 (1st subgrid) Second Yes
_distortion.gsb Use nodata = -1
A66_National_13_09_01.gsb ICSM Australia 1e-3 / 8e-3 / 1e-2 (1st subgrid) Second Yes
CA61_003.GSB IBGE Brazil Metre Yes
CA7072_003.GSB IBGE Brazil Metre Yes
SAD69_003.GSB IBGE Brazil Metre Yes
SAD96_003.GSB IBGE Brazil Metre Yes

Remarks:

  • bd72lb72_etrs89lb08.gsb : documented by EPSG to have a 0.01 m accuracy
  • D73_ETRS89_geo.gsb: the lat accuracy is 1.5e-3 and the lon accuracy is 1.9e-3. If using a latitude = 36 degree, 1.9e-3 * cos(36 degree) ~= 1.5 e-3. Hence a hint the unit might be seconds
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