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