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| GeoCommunity Mailing List |
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| Mailing List Archives |
| Subject: | GISList: Projected Data |
| Date: |
11/09/2002 09:21:36 PM |
| From: |
DuBose Griffin |
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Good Afternoon,
Again, I need a little clarity. Bear with me as I explain this and the
answer I am looking for is probably a lot simpler than the length of the
question. I am using ArcView 3.2a. Here is the ultimate question
(repeated at bottom of email):
How do you put projected data on your projection of choice?????? And how
do you know if the measurement that you are getting is accurate????
Here is what I did
1. I went through all the trouble to determine and choose the correct
projection for this data= Albers Equal Area.
2. So then I took plain old decimal degrees data (unprojected data) and
I reprojected it in 3 different ways to examine any discrepancies
between the methods.
A. Reprojected on the fly by changing the projection in View properties.
I converted the shape files to new shape files after changing the
projection (least favorable method).
B. I used the projection utility wizard to reproject the shape files.
C. I used the projector script to reproject the shape files.
So now I have 3 sets of the reprojected shape files using 3 different
methods. So far there does not seem to be any difference between the
files. Something that may be of interest to some of you.
So now I wanted to put one set of these shape files into a view that has
the projection I chose (Albers). When I do this, the shape files do not
show up.
THEY DO SHOW UP HOWEVER WHEN I ADD THEM TO A BLANK VIEW WITH THE VIEW
PROPERTIES MAP UNITS SET ON METERS.
**********HERE IS THE SUPER FRUSTRATING PART, WHEN I MEASURE THE
DISTANCE BETWEEN 2 POINTS ON THE PROJECTED AND UNPROJECTED DATA THE
DISTANCE IS THE SAME.
THE WHOLE POINT OF THIS WAS TO BE ABLE TO MEASURE AREA ACCURATELY IN
SQUARE KILOMETERS. IF THERE IS NO DIFFERENCE BETWEEN THE PROJECTED AND
UNPROJECTED WHY DID I SPEND 5 HOURS TRYING TO PROJECT ALL THESE SHAPE
FILES?????
IT SEEMS THAT SETTING THE PROJECTION IS IRREVELANT TO THE DATA IF THE
DATA IS PROJECTED....
How do you put projected data on your projection of choice?????? And how
do you know if the measurement that you are getting is accurate????
Very Frustrated,
DuBose Griffin
** Please Note New Phone and Fax Numbers Below
***********************************************************
Ms. DuBose Griffin
Endangered Species Biologist
GIS Analyst
Sea Turtle Desk
South Carolina Department of Natural Resources
Wildlife and Freshwater Fisheries Division
Wildlife Diversity Section
217 Fort Johnson Road
Post Office Box 12559
Charleston, South Carolina 29422-2559
U.S.A.
Email: griffind@mrd.dnr.state.sc.us
Voice: 843-953-9016
Fax: 843-953-9353
URL: http://water.dnr.state.sc.us/
***********************************************************
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