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<DIV dir=ltr align=left><SPAN class=520300219-06092006><FONT face=Tahoma
color=#0000ff>Here's Dave Doyle's response. Please note that the height
component in NAD 83 (1990) HPGN/HARN is the ellipsoid (essentially the GPS)
height, which is NOT the same as NAVD 88 vertical datum, which is based on tidal
(a.k.a. sea-level) reference measurements. Most elevations (maps, surveys,
etc.) are referenced to the NAVD 88 datum.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=520300219-06092006><FONT face=Tahoma
color=#0000ff></FONT></SPAN> </DIV>
<DIV><B><SPAN lang=en-us><FONT face="Brush Script MT" size=6>--
John</FONT></SPAN></B><SPAN lang=en-us></SPAN> </DIV>
<DIV><FONT face=Tahoma color=#0000ff><SPAN
class=520300219-06092006>------------------------------------------------------------------------</SPAN></FONT></DIV>
<DIV>
<P><FONT face=Tahoma color=#0000ff>John</FONT></P>
<P><FONT face=Tahoma color=#0000ff>Good questions. Hopefully I can answer them
without getting too long winded (which is very hard for me).</FONT></P>
<P><FONT face=Tahoma color=#0000ff>NAD 27 was a purely horizontal
datum</FONT></P>
<P><FONT face=Tahoma color=#0000ff>NAD 83 in it's original solution of 1986, now
referenced as NAD 83<SPAN class=520300219-06092006> </SPAN>(1986) was also
purely horizontal.</FONT></P>
<P><FONT face=Tahoma color=#0000ff>NAD 83<SPAN class=520300219-06092006>
</SPAN>(1990) is both HPGN and HARN. In 1992 the name of the GPS survey program
was called the High Precision GPS Network (HPGN). Sometime in<SPAN
class=520300219-06092006> </SPAN>1992 someone at NGS (not me) had the idea to
change it to High Accuracy Reference Network (HARN). So regardless of the name
change the process or concept is still the same. Now, for the first time a
vertical component was added which did not exist with NAD 27 and NAD 83 (1986),
but it's the ellipsoid height component, which is NOT the NAVD 88. NAVD<SPAN
class=520300219-06092006> </SPAN>88 is strictly a vertical datum and is not in
any way related to NAD 83 other than control points that are the realization of
these two datums may have well determined values.</FONT></P>
<P><FONT face=Tahoma color=#0000ff>I hope this makes some sense. If it's not
clear please call me</FONT></P>
<P><FONT face=Tahoma color=#0000ff>(301-713-3178) and I will be happy to explain
this in greater detail.</FONT></P>
<P><FONT face=Tahoma color=#0000ff>Regards -- Dave Doyle</FONT></P></DIV><BR>
<DIV class=OutlookMessageHeader lang=en-us dir=ltr align=left>
<HR tabIndex=-1>
<FONT face=Tahoma size=2><B>From:</B> shrug-l-bounces@lists.dep.state.fl.us
[mailto:shrug-l-bounces@lists.dep.state.fl.us] <B>On Behalf Of </B>Thomas,
Jim<BR><B>Sent:</B> Wednesday, September 06, 2006 1:32 PM<BR><B>To:</B>
shrug-l@lists.dep.state.fl.us<BR><B>Subject:</B> FW: shrug-l:
NAD83/90<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV dir=ltr align=left><SPAN class=011522817-06092006><FONT face=Arial
color=#0000ff size=2>I've done more research and the 90 part of NAD83/90 seems
to refer to the 1990 adjustment (as John said below). This is new to me as
I've never referred to NAD83 in another way. Does anyone know what
the latest adjustment is? and what ESRI's ArcGIS uses?</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=011522817-06092006><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=011522817-06092006><FONT face=Arial
color=#0000ff size=2>I'll have to do more homework on this one. Thanks for
your help.</FONT></SPAN></DIV><BR>
<DIV class=OutlookMessageHeader lang=en-us dir=ltr align=left>
<HR tabIndex=-1>
<FONT face=Tahoma size=2><B>From:</B> Sykes, John
[mailto:John.Sykes@dep.state.fl.us] <BR><B>Sent:</B> Wednesday, September 06,
2006 11:59 AM<BR><B>To:</B> Thomas, Jim<BR><B>Subject:</B> RE: shrug-l:
NAD83/90<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV dir=ltr align=left><SPAN class=438395015-06092006><FONT face=Tahoma
color=#0000ff>My understanding is that the NAD83 is the "standard" replacement
for NAD27.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=438395015-06092006><FONT face=Tahoma
color=#0000ff></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=438395015-06092006><FONT face=Tahoma
color=#0000ff>NAD83 HARN and NAD83/90HPGN are, essentially, the same.
Originally it was called the High Precision Geographical Network, but was
subsequently changed to High Accuracy Regional Network (or something like
that).</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=438395015-06092006><FONT face=Tahoma
color=#0000ff></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=438395015-06092006><FONT face=Tahoma
color=#0000ff>The difference between NAD83 and NAD27 is several meters (up to
around 100 meters in parts of Florida), but NAD83 to NAD83 HARN is usually in
the centimeter range (in most of Florida).</FONT></SPAN></DIV>
<DIV><FONT face=Tahoma color=#0000ff></FONT> </DIV>
<DIV><SPAN class=438395015-06092006><FONT face=Tahoma color=#0000ff>Note:
It is also my understanding that the NAD83/90 is the "standard" version of NAD83
and, therefore, is redundant. So usually you would see just NAD83 or NAD83
HARN, the "90" is assumed (not necessarily the case with HARN, which I believe
is set to a later epoch [2004????]). HPGN is no longer used. If
you want to confirm the epoch, look up a CORS station in the NGS datasheets, it
will give the epoch information as well as the drift information (Florida is
drifting northwest at about 1 cm/yr).</FONT></SPAN></DIV><!-- Converted from text/rtf format -->
<P><B><SPAN lang=en-us><FONT face="Brush Script MT" size=6>--
John</FONT></SPAN></B><SPAN lang=en-us></SPAN> </P>
<DIV> </DIV><BR>
<DIV class=OutlookMessageHeader lang=en-us dir=ltr align=left>
<HR tabIndex=-1>
<FONT face=Tahoma size=2><B>From:</B> shrug-l-bounces@lists.dep.state.fl.us
[mailto:shrug-l-bounces@lists.dep.state.fl.us] <B>On Behalf Of </B>Thomas,
Jim<BR><B>Sent:</B> Wednesday, September 06, 2006 11:27 AM<BR><B>To:</B>
shrug-l@lists.dep.state.fl.us<BR><B>Subject:</B> shrug-l:
NAD83/90<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV><FONT face=Arial size=2><SPAN class=683431715-06092006>Can someone briefly
explain the difference among the following.</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=683431715-06092006></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN
class=683431715-06092006>NAD83</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN class=683431715-06092006>NAD83
HARN</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN class=683431715-06092006>NAD83/90
HPGN</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=683431715-06092006></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN class=683431715-06092006>Is NAD83 HARN the
same as NAD83/90 HPGN?</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=683431715-06092006></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN class=683431715-06092006>I'm getting requests
to have coordinates reported in NAD83/90 and need to understand the
difference.</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=683431715-06092006></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN class=683431715-06092006>Thanks for you
help.</SPAN></FONT></DIV></BODY></HTML>