Just to close this out, New York New Jersey FEMA advisory Base Flood Elevations are ESPG:3857 > From: sgl...@hotmail.com > To: g...@ir.bbn.com; gdal-dev@lists.osgeo.org > Date: Sat, 2 Feb 2013 11:39:23 -0500 > Subject: Re: [gdal-dev] Fema Flood Maps NAV88 - proj4text > > > The parcels are, of course, horizontal only datum. > from the .prj > > PROJCS["NAD_1983_StatePlane_New_Jersey_FIPS_2900_Feet", > GEOGCS["GCS_North_American_1983", > DATUM["D_North_American_1983",SPHEROID["GRS_1980",6378137.0,298.257222101]], > PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]], > PROJECTION["Transverse_Mercator"],PARAMETER["False_Easting",492125.0], > PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",-74.5], > PARAMETER["Scale_Factor",0.9999], > PARAMETER["Latitude_Of_Origin",38.83333333333334],UNIT["Foot_US",0.3048006096012192]] > > and from a representative flood map .prj > > PROJCS["WGS_1984_Web_Mercator_Auxiliary_Sphere",GEOGCS["GCS_WGS_1984", > DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137.0,298.257223563]], > PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]], > PROJECTION["Mercator_Auxiliary_Sphere"],PARAMETER["False_Easting",0.0], > PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",0.0], > PARAMETER["Standard_Parallel_1",0.0],PARAMETER["Auxiliary_Sphere_Type",0.0],UNIT["Meter",1.0]] > > which seems now, looking at them, should just be a standard transform. But > then this from > Adv_MO_FloodZones.shp.xml > > -<geodetic> > <horizdn>GCS WGS 1984</horizdn> > <ellips>World Geodetic System 1984</ellips> > <semiaxis>6378137.000000</semiaxis> > <denflat>298.257222</denflat> > </geodetic> > </horizsys> > <vertsys> > <gridsysn>NAVD88</gridsysn> > <plandu>FEET</plandu> > </vertsys> > > well, I'll continue to muddle and head scratch. > ---------------------------------------- > > From: g...@ir.bbn.com > > To: sgl...@hotmail.com > > CC: gdal-dev@lists.osgeo.org > > Subject: Re: [gdal-dev] Fema Flood Maps NAV88 - proj4text > > Date: Sat, 2 Feb 2013 08:21:11 -0500 > > > > > > You may want to join the proj list. > > > > Your parcel maps are in EPSG (ESRI, really) 102711, which is: > > > > http://spatialreference.org/ref/esri/102711/ > > > > This is a horizontal-only datum. I have only encountered horizontal > > data in parcel maps (Mass, not NJ). Do you have any heights presented > > with this? If so, do you understand what they are? If there are > > heights, I would expect they are in NAVD88, but they could be in > > ellipsoidal height relative to the GRS80 ellipsoid and the NAD83 > > orientation. Ellipsoidal height is relatively recent, and estimated > > orthometric heights based on geoid models and observed ellispoidal > > heights is where NGS is heading, but I would doubt most practitioners > > are doing that yet. > > > > Your flood maps are in EPSG:5703: > > http://spatialreference.org/ref/epsg/5703/ > > This is a vertical-only datum. Are there horizontal coordinates? If > > so, what are they in? I would expect some sort of NAD83, and their > > purpose is to locate where the heights are given. > > > > So what I think you want is to know the NAVD88 heights around the parcel > > of interest, so you therefore want all your horizontal coordinates in > > NAD83, and to leave the height in NAVD88. (Water flows downhill in > > NAVD88, but does not necessarily flow towards lower height values in > > ellipsoidal height coordinates!!) > > > > You were talking about a geoid file, which presumably transforms NAVD88 > > height to something, which is probably ellipsoidal height based on > > NAD83. That's the typical geoid model published by NGS. > > There are also geoid models from WGS84 ellipsoidal height, but these do > > not transform to NAVD88. > > > > Do you have any height data in other than NAVD88? If so, please > > describe it. > > _______________________________________________ > gdal-dev mailing list > gdal-dev@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/gdal-dev
_______________________________________________ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev
