Hello Stephen -
For the Mercator projection, bearings are true but scale is only true at
the tangent(s). Either change the projection parameters to put the line of
tangency closer to the area in which you wish to measure or choose another
projection (like a conic) to get better distance calculations.
Quoting from Snider (1987):
"Linear scale is true along the equator only (line of tangency), or along
two parallels equidistant from the equator (the secant form)."
Cheers,
Lindsay Giles
Senior GIS Analyst
AXYS Environmental Consulting Ltd
Suite 600-555 4th Ave. SW
Calgary, AB
CANADA
T2P 3E7
e-mail: [EMAIL PROTECTED]
Main Office: 403-269-5150
Direct Line: 403-750-7671
Fax: 403-269-5245
Visit our web site at http://www.axys.net
-----Original Message-----
From: Stephen Baig [SMTP:[EMAIL PROTECTED]]
Sent: Tuesday, September 19, 2000 7:58 AM
To: [EMAIL PROTECTED]
Subject: MI Help - printing to scale - again
Hello list,
I need again to ask for help with this touchy subject. I use MI to print
the base charts the Hurricane Center uses to plot tropical weather. The
base chart is a Mercator projection of the Atlantic Ocean basin, with
surrounding land. The distance from feature to land, and other
measurements, is correct in MI as measured on-screen, and the same
distances are correct when they are laid off against the meridians of the
printed chart. So at least we aren't telling people the storm is 500 miles
away when it really is just 300 miles off. The chart is printed at a
"called out" scale of 1:6,000,000. That is, in the Layout mode, when the
Frame Object menu pops up the scale is set to 1:6,000.000.
The problem is that the printed distance between meridians is not to the
1:6,000,000 scale!!! At that scale I calculate the distance between
meridians should be about 1.85 cm. The as-printed distance is about 1.6
cm. That means the printed scale really is about 1:6,945,000. The
printer, an HP 2500 PC, has been checked and has an error both vertical
and horizontal of about 1 mm in 750 mm.
The problem could be ignored by using 1:6,945,000 in the legend, but I'd
rather learn how to get the "real" scale to print.
Thanks for reading this far. Standing by for assistance with 1) a new roll
of paper in the plotter and 2) palm extended and forehead within striking
distance.
Dr. Stephen Baig
Oceanographer,
National Hurricane Center
Miami, FL
305.229.4444
[EMAIL PROTECTED]
----------------------------------------------------------------------
To unsubscribe from this list, send e-mail to [EMAIL PROTECTED] and put
"unsubscribe MAPINFO-L" in the message body, or contact [EMAIL PROTECTED]
----------------------------------------------------------------------
To unsubscribe from this list, send e-mail to [EMAIL PROTECTED] and put
"unsubscribe MAPINFO-L" in the message body, or contact [EMAIL PROTECTED]
