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+# README.us_nga
+
+The files in this section result from the conversion of datasets originating
+from [US NOAA](https://www.ngs.noaa.gov)
+
+## Included grids
+
+### USA: NAD83 -> NAD83 (HARN/HPGN)
+
+*Source*: [.los/.las files coming from NOAA](https://www.ngs.noaa.gov/PC_PROD/NADCON/NADCON.zip)  
+*Format*: GeoTIFF converted from NTv2  
+*License*: Public Domain
+
+Grid data for high precision conversion of geographic coordinates from
+the original NAD83 (1986) (EPSG:4269) to NAD83 High Precision Geodetic Networks
+(HPGNs) (EPSG:4152), also referred to as High Accuracy Reference Networks (HARNs).
+NAD 83 coordinates based on the HPGN/HARN surveys changed approximately 0.2
+to 1.0 meter relative to the original NAD 83 (1986) adjustment.
+
+Those files have been converted to NTv2 grids with the
+[build_nad83_harn.sh](https://raw.githubusercontent.com/OSGeo/proj-datumgrid/master/north-america/build_nad83_harn.sh) script.
+
+* *hpgn.tif (51 files)
+
+### Continental USA VERTCON: NGVD (19)29 height to NAVD (19)88 height
+
+*Source*: converted from [NOAA VERTCON .94 grids](https://www.ngs.noaa.gov/PC_PROD/VERTCON/)  
+*Converter*: vertcon_94_to_gtx.py  
+*Format*: GeoTIFF converted from GTX  
+*License*: Public Domain
+
+Transform NGVD (19)29 height to NAVD (19)88 height. The .tif files contain
+the offset to add to NGVD 29 heights to get NAVD 88 heights.
+
+The horizontal grid coordinates may be referenced to NAD27 or NAD83
+
+* vertconc.tif
+* vertcone.tif
+* vertconw.tif
+
+### USA GEOID1999 model (superseded): NAVD88 height to NAD83
+
+*Source*: converted from [NOAA NGS .bin grids](https://geodesy.noaa.gov/GEOID/GEOID99/)  
+*Converter*: build_g1999.sh  
+*Format*: GeoTIFF converted from GTX  
+*License*: Public Domain
+
+The GEOID99 model is known as a hybrid geoid model, combining
+gravimetric information with GPS ellipsoid heights on leveled bench marks.
+The GEOID99 model was developed to support direct conversion between
+NAD 83 GPS ellipsoidal heights and NAVD 88 orthometric heights.
+
+It is superseded by later GEOIDxx models
+
+* g1999u01.tif to g1999u08.tif : Conterminous US
+* g1999a01.tif to g1999a04.tif : Alaska
+* g1999h01.tif : Hawaii
+* g1999p01.tif : Puerto Rico
+
+### USA GEOID2003 model (superseded): NAVD88 height to NAD83
+
+*Source*: converted from [NOAA NGS .bin grids](https://geodesy.noaa.gov/GEOID/GEOID03/)  
+*Converter*: build_g2003.sh  
+*Format*: GeoTIFF converted from GTX  
+*License*: Public Domain
+
+The GEOID03 model is known as a hybrid geoid model, combining
+gravimetric information with GPS ellipsoid heights on leveled bench marks.
+The GEOID03 model was developed to support direct conversion between
+NAD 83 GPS ellipsoidal heights and NAVD 88 orthometric heights.
+
+It is superseded by later GEOIDxx models
+
+* geoid03_conus.tif : Conterminous US
+* g2003a01.tif to g2003a04.tif : Alaska
+* g2003h01.tif : Hawaii
+* g2003p01.tif : Puerto Rico
+
+### USA GEOID2006 model (superseded): NAVD88 height to NAD83 (Alaska only)
+
+*Source*: converted from [NOAA NGS .bin grids](https://geodesy.noaa.gov/GEOID/GEOID06/)  
+*Converter*: build_g2006.sh  
+*Format*: GeoTIFF converted from GTX  
+*License*: Public Domain
+
+GEOID06 is a refined hybrid geoid model for Alaska only.
+
+GEOID06 converts between the U.S. ellipsoidal datum, NAD 83, and the U.S.
+vertical datum, NAVD 88. GEOID06 is built largely on the USGG2003 gravimetric geoid.
+
+It is superseded by later GEOIDxx models
+
+* geoid06_ak.tif : Alaska
+
+### USA GEOID2009 model (superseded): NAVD88/PRVD02/VIVD09/GUVD04 height to NAD83
+
+*Source*: converted from [NOAA NGS .bin grids](https://www.ngs.noaa.gov/GEOID/GEOID09/)  
+*Converter*: build_g2009.sh  
+*Format*: GeoTIFF converted from GTX  
+*License*: Public Domain
+
+The GEOID09 model is known as a hybrid geoid model, as it is modified
+from a gravimetric model to fit GPS ellipsoid heights on leveled bench marks.
+The GEOID09 model refers to a GRS-80 shaped ellipsoid,
+centered at the NAD83 origin.  It supports direct conversion between
+NAD83 GPS ellipsoidal heights and NAVD88, GUVD04 and ASVD03 orthometric heights,
+and will support future vertical datums PRVD02 nad VIVD09.
+
+* geoid09_conus.tif : Conterminous US.
+* geoid09_ak.tif : Alaska.
+* g2009h01.tif : Hawaii
+* g2009g01.tif : Guam and Northern Mariana Islands.
+* g2009s01.tif : American Samoa.
+* g2009p01.tif : Puerto Rico / U.S. Vigin Islands.
+
+### USA GEOID12B model (partial superseded): NAVD88/PRVD02/VIVD09/GUVD04/NMVD03/ASVD02 height to NAD83(2011)/NAD83(MA11)/NAD83(PA11)
+
+*Source*: converted from [NOAA NGS .bin grids](https://www.ngs.noaa.gov/GEOID/GEOID12B/)  
+*Converter*: build_g2012.sh  
+*Format*: GeoTIFF converted from GTX  
+*License*: Public Domain
+
+GEOID12B is a hybrid geoid height model that can transform between the relevant
+vertical datum for each region to a NAD 83 ellipsoid height
+See https://www.ngs.noaa.gov/GEOID/GEOID12B/faq_2012B.shtml for more details.
+
+* g2012bu0.tif : Conterminous US, referenced to NAD83(2011). Vertical datum: NAVD88
+* g2012ba0.tif : Alaska, referenced to NAD83(2011). Vertical datum: NAVD88
+* g2012bh0.tif : Hawaii, referenced to NAD83(PA11). Vertical datum: identical to that of USGG2012, which is offset by 50-60 cm from some Local Tidal bench mark values. 
+* g2012bg0.tif : Guam and Northern Mariana Islands, referenced to NAD83(PA11). Vertical datum: GUVD04/NMVD03
+* g2012bs0.tif : American Samoa, referenced to NAD83 (PA11). Vertical datum: ASVD02
+* g2012bp0.tif : Puerto Rico / U.S. Vigin Islands, referenced to NAD83(2011). Vertical datum: PRVD02 and VIVD09
+
+The g2012bu0.tif and g2012bp0.tif grids are superseded by the
+g2018p0.tif and g2018p0.tif grids of GEOID18.
+
+### USA GEOID18 model: NAVD88/PRVD02 height to NAD83(2011)
+
+*Source*: converted from [NOAA NGS .bin grids](https://www.ngs.noaa.gov/GEOID/GEOID18/)  
+*Converter*: build_g2018.sh  
+*Format*: GeoTIFF converted from GTX  
+*License*: Public Domain
+
+GEOID18 is intended for use with coordinates in the North American Datum of 1983 (2011)
+[NAD 83 (2011) epoch 2010.00]. It provides orthometric heights consistent with the
+North American Vertical Datum of 1988 (NAVD 88), the Puerto Rico Vertical Datum of
+2002 (PRVD02), or the Virgin Islands Vertical Datum of 2009 (VIVD09).
+
+GEOID18 covers CONUS, Puerto Rico, and the U.S. Virgin Islands and supersedes
+GEOID12B in these regions. GEOID18 does NOT cover Alaska, Hawaii, Guam and the
+Commonwealth of the Northern Mariana Islands (CNMI) where users should continue
+to use GEOID12B.
+
+* g2018u0.tif : Conterminous US, referenced to NAD83(2011). Vertical datum: NAVD88
+* g2018p0.tif : Puerto Rico / U.S. Vigin Islands, referenced to NAD83(2011). Vertical datum: PRVD02 and VIVD09