shrug-l: Lat-Long

Thomas, Jim jim_thomas at golder.com
Thu Dec 22 12:22:42 EST 2005


I've tested my theory - the Export Data tool created a brand new
shapefile in a completely different geometry consistent with the data
frame's coordinate system (i tested this by 'clearing' the data frame
coordinate system - that's the same as bringing the two datasets into
ArcView GIS).  My point is that the Export Data tools will re-project.
Although, is appears there is no guarantee that it will transform the
datums correctly... "If your data's geographic coordinate system
<BLOCKED::javascript:glossary_geographic_coordinate_system22168.Click()>
uses a different datum <BLOCKED::javascript:glossary_datum22168.Click()>
than that of the new feature class, you will likely write spatially
inaccurate data."
 
ESRI would not program the tool and keep it in ArcGIS 9 if the option
wasn't dependable most of the time.  Is there anyone from ESRI who would
like to chime in?

________________________________

From: Hughes, Ronald [mailto:Ronald.Hughes at dep.state.fl.us] 
Sent: Thursday, December 22, 2005 12:08 PM
To: Paulsen, Janis; Thomas, Jim
Cc: shrug-l at lists.dep.state.fl.us
Subject: RE: shrug-l: Lat-Long


Thank you Janis.  This is the point I was making.  As I'd mentioned
previously, it is the "on the fly projection" in ArcGIS that makes them
to overlay, but as you pointed out, when you use a product that doesn't
have "on the fly projection" you see that the geometry didn't change.
Only the projection definition changed.
 
________________________________

From: Paulsen, Janis 
Sent: Thursday, December 22, 2005 12:04 PM
To: Hughes, Ronald; Thomas, Jim
Cc: shrug-l at lists.dep.state.fl.us
Subject: RE: shrug-l: Lat-Long
 
I thought I'd jump in here.  I just ran a little experiment.  I brought
in two differently projected shapefiles into ArcMap 9.0. They were
reprojected on the fly in ArcMap. In ArcMap, both shapefiles overlaid
each other correctly.  I set the dataframe coordinate system to GCS
North American NAD 83 HARN.  I did a data export on both shapefiles
selecting the "use same coordinate system as data frame" option.  I then
brought both shapefiles into ArcView 3.x.  The both loaded into the apr,
but did not overlay eachother.  This tells me that AcrView allowed them
both to be brought in because they were assigned the same coordinate
system, but they were not actually reprojected geometrically, since they
did not draw in the same place in space.  Interesting.
Janis
 
-----Original Message-----
From: shrug-l-bounces at lists.dep.state.fl.us
[mailto:shrug-l-bounces at lists.dep.state.fl.us] On Behalf Of Hughes,
Ronald
Sent: Thursday, December 22, 2005 11:47 AM
To: Thomas, Jim
Cc: shrug-l at lists.dep.state.fl.us
Subject: RE: shrug-l: Lat-Long
 
Sorry Thomas, but it doesn't re-project.  That method you used simply
re-defines the projection unless they've changed it in Version 9x (which
is highly doubtful).  If you want to change the geometry, you'll need to
use ArcToolbox.  It's simply isn't good practice to assign incorrect
projection files to spatial data.
 
I hope that clears things up.
 
________________________________

From: Thomas, Jim [mailto:jim_thomas at golder.com] 
Sent: Thursday, December 22, 2005 11:33 AM
To: Hughes, Ronald
Cc: shrug-l at lists.dep.state.fl.us
Subject: RE: shrug-l: Lat-Long
 
It's not simply re-defining.  It's re-projecting.  
 
When you use the 'Export Data...' tool from ArcMap you can select the
export coordinate system (see attached jpg).  It will re-project the
data to what you define.
 
The Shruggers can use whatever method works best for them.
 
 
________________________________

From: Hughes, Ronald [mailto:Ronald.Hughes at dep.state.fl.us] 
Sent: Thursday, December 22, 2005 11:23 AM
To: Thomas, Jim; shrug-l at lists.dep.state.fl.us
Subject: RE: shrug-l: Lat-Long
Actually Thomas, the problem with that is that the NEW shapefile will
still be in STATEPLANE projection.  In other words, the geometry or
"physical condition" remains as STATEPLANE.  All you've done is
re-define the projection file.  Defining a projection and actually
RE-PROJECTING a shapefile are two separate things.  Re-projecting a
shapefile involves changing its geometry and topology while re-defining
the projection only changes a text file.  You never want to assign an
incorrect projection file to a shapefile because it tends to lead to
trouble if you send that file to somebody else and then they try to
re-project that shapefile using incorrect projection information.  
 
The reason that it appears to work for you is because of the ArcGIS
"projection on the fly" capability.  If you were to use a GIS product
that doesn't project "on-the-fly" you would see that re-defining the
projection file hasn't changed the geometry of the shapefile: it's still
in STATEPLANE.
 
As far as datum transformation is concerned, when switching between
certain coordinate systems, you may wind up using different datum and
need to transform from one datum to the next.  For example when I was
using ArcGIS version 8x and projected from STATEPLANE NAD83 datum to
Geographic North American 1983 HARN datum I would get the following
error message:
 

 
I would then have to set the transformation from NAD_1983 to
HARN_Florida:
 

 
Many people think that redefining the projection of a shapefile is the
same and projecting a shapefile but it is not.  I hope that I've
contributed to clearing this up.
 
Good luck,
Ron
 
 
________________________________

From: Thomas, Jim [mailto:jim_thomas at golder.com] 
Sent: Thursday, December 22, 2005 10:52 AM
To: Hughes, Ronald; shrug-l at lists.dep.state.fl.us
Subject: RE: shrug-l: Lat-Long
 
The steps I listed will work too.  You can export a NEW shapefile from
ArcMap in the spatial reference of the data frame (which can be
different than the original shapefile).  As long as everything is
defined correctly, you'll have no problem.  I do it all the time.
 
As far as the datum transformation list... that's a good question. I
always wondered that.
 
 
 
________________________________

From: shrug-l-bounces at lists.dep.state.fl.us
[mailto:shrug-l-bounces at lists.dep.state.fl.us] On Behalf Of Hughes,
Ronald
Sent: Thursday, December 22, 2005 10:32 AM
To: shrug-l at lists.dep.state.fl.us
Subject: RE: shrug-l: Lat-Long
Actually, you need to use ArcToolbox to reproject the shapefile.  All
the steps mention below do is re-define the projection file.  It would
be analogous to assigning a new mailing address to you home without
physically moving it from its current location.  In other words, if your
house sits at 800 Main Street and you change the address to 21 Jump
Street, the house still remains at 800 Main Street.  
 
The Present version of ArcToolbox that I have (ArcGIS 9.1) is different
from that what I'd previously had but it appears to work the same way.
 
Open up ArcToolbox and select Data Management Tools --> Projections and
Transformations --> Project. 
 
Click on Project and a menu should come up that asks for your imput
feature and output (in ArcGIS 9.1 it automatically assigns a 'P' at the
end of the name of the input and places it in the output.  Select the
projection that you want for the output by clicking on the button to the
right of the input window.  That will bring up a menu called "Spatial
Reference Properties".
 
1.) Click the button labeled "Select".
 
2.) Click the Geographic Coordinate Systems folder
 
3.) Click the North America folder and select the coordinate system that
you want (probably North American 1983 HARN.prj).
 
4.) Click the "Add" button and select "OK".
 
If you have any other questions just ask.  
 
Good luck!
 
-----Original Message-----
From: shrug-l-bounces at lists.dep.state.fl.us
[mailto:shrug-l-bounces at lists.dep.state.fl.us] On Behalf Of Thomas, Jim
Sent: Thursday, December 22, 2005 9:34 AM
To: tdarsey at hsa.cc; shrug-l at lists.dep.state.fl.us
Subject: RE: shrug-l: Lat-Long
 
1. Define your shapefile's spatial reference in ArcCatalog
2. Load the shapefile into ArcMap
3. Change the data frame spatial reference to Lat/Long
4. Export the new shapefile using the data frame's spatial reference
(during export)
5. That's it.
 
________________________________

From: shrug-l-bounces at lists.dep.state.fl.us
[mailto:shrug-l-bounces at lists.dep.state.fl.us] On Behalf Of Tony Darsey
Sent: Thursday, December 22, 2005 9:30 AM
To: shrug-l at lists.dep.state.fl.us
Subject: shrug-l: Lat-Long
Can anyone tell me how to convert a shape file from State Plane to
Lat/Long?
Thanks, 
Tony Darsey 
HSA Consulting Group, Inc. 
1311 Executive Center Drive, Suite 255 
Tallahassee, FL 32301 
Phone (850) 309-7510 
Fax     (850) 309-7510 
Cell     (850) 508-6477 
email   tdarsey at hsa.cc 
 
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