<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=Content-Type content="text/html; charset=us-ascii">
<META content="MSHTML 6.00.2900.2873" name=GENERATOR></HEAD>
<BODY>
<DIV dir=ltr align=left><SPAN class=336372515-04052006><FONT face=Tahoma
color=#0000ff>OK, I saw your second message. I've been there
too.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=336372515-04052006><FONT face=Tahoma
color=#0000ff></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=336372515-04052006><FONT face=Tahoma
color=#0000ff>About my first post, I forgot to mention two things. First,
conversion from NAD27 to NAD83 is not exact. The software uses a
best-fit conversion using a grid developed by the National Geodetic
Service, so errors may be in the 10 to 20 cm range depending on where you are
(not in Florida however, our grid is quite tight). NAD83 to HARN also
depends on the State's network of CORS stations (again, quite good in
Florida). There is a new iteration of the HARN in the mill, which will be
coming out in February 2007. Supposedly, this would reduce the distance
error from a point in Key West to a point in Seattle, Washington to about
+/- 2 cm.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=336372515-04052006><FONT face=Tahoma
color=#0000ff></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=336372515-04052006><FONT face=Tahoma
color=#0000ff>Unlike the NAD conversions, the conversion from Lat-Long to FDEP
Albers coordinates IS an exact mathematical relationship. So it's
accuracy is limited only by the mathematical precision of the computer.
Oh, by the way. I forgot to mention in my last post, Double Precision = 64
bits, Triple Precision = 80 bits and Quad Precision = 128 bits in an
Intel-based PC, or about 15, 18 and 30 significant digits,
respectively.</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> Thursday, May 04, 2006 11:14 AM<BR><B>To:</B>
shrug-l@lists.dep.state.fl.us<BR><B>Subject:</B> shrug-l: NAD 83 to NAD83
HARN<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=397370415-04052006>Shruggers,</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=397370415-04052006></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN class=397370415-04052006>Is this
true?</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=397370415-04052006></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN class=397370415-04052006>"<FONT
face="Times New Roman" size=3>To project data from State Plane NAD 27 West to
NAD 83 HARN takes two (2) transformations."</FONT></SPAN></FONT></DIV>
<DIV><FONT face="Times New Roman" size=3><SPAN
class=397370415-04052006></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN class=397370415-04052006>I'm dealing with
data referenced as FLSP-W NAD83 HARN and it's not overlaying my NAD27
data. Could it be that ArcMap is incorrectly projecting on the fly?
If I change the reference system from NAD83 HARN to NAD83, it overlays
properly. Am I missing something?</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
class=397370415-04052006></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN class=397370415-04052006>Jim
T.</SPAN></FONT></DIV></BODY></HTML>