<div dir="ltr">Hello,<div><br></div><div>As we move to registering our vdatum grids in EPSG, we needed to develop a stop gap solution, describing our custom datums in WKT for archival.  These would be derived datums based on elheight or geoid height, with proj vgrid pipelines applied to get to water level datum.  We are thinking about using something like this:</div><div><br></div><div>VERTCRS["NOAA Chart Datum",<br>                  BASEVERTCRS["NAD83(2011) Height",<br>                                              VDATUM["NAD83(2011) Height"],<br>                                              ID["EPSG",6319]],<br>                  DERIVINGCONVERSION["NAD83(2011) Height to NOAA Mean Lower Low Water",<br>                                               METHOD["VDatum_VXXX gtx grid transformation",<br>                                                  ID["EPSG",1084]],<br>                                                PARAMETERFILE['g2012bu0', 'core\\geoid12b\\g2012bu0.gtx',<br>                                                  ID[“NOAA VDatum”, “NAD83 to Geoid12B”, “10/23/2012”]],<br>                                                PARAMETERFILE['tss', 'CAORblan01_8301\\tss.gtx',<br>                                                  ID[“NOAA VDatum”, “Geoid12B to Tss", “06/20/2019”]],<br>                                                PARAMETERFILE['mllw', 'CAORblan01_8301\\mllw.gtx',<br>                                                  ID[“NOAA VDatum”, “Tss to Mean Lower Low Water”, “06/20/2019”]]],<br>                    VDATUM["NOAA Chart Datum"],<br>                    CS[vertical,1],<br>                          AXIS["gravity-related height (H)",up],<br>                          LENGTHUNIT["metre",1]]<br></div><div><br></div><div>I know this isn't something we could use in PROJ in the same way that a registered EPSG reference could, but we could at least have something describing what we do for archival.  I'm thinking of building some code to manually translate a move between two of these WKT strings into a pipeline operation.</div><div><br></div><div>Hopefully that made sense.  Please let me know if you have any suggestions.</div><div><br></div><div>Thanks,<br>Eric</div><div><div><br></div>-- <br><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><span><font color="#0000ff">Eric Younkin<br>Physical Scientist<br></font></span></div><div dir="ltr"><span><font color="#0000ff">NOAA OCS, </font></span><span style="color:rgb(0,0,255);font-size:12.8px">Hydrographic Systems and Technology Branch</span></div><div dir="ltr"><span><font color="#0000ff">1315 East-West Highway</font></span></div><div dir="ltr"><span><font color="#0000ff">N/CS11, Room 6604<br>Silver Spring, MD 20910</font></span></div><div><span><font color="#0000ff">Office: </font></span><span style="font-family:arial,sans,sans-serif;font-size:13px;white-space:pre-wrap"><font color="#0000ff">240-847-8208</font></span></div><div dir="ltr"><span><font color="#0000ff">
Cell: 828-331-8197</font><br>
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