[MetaCRS] plotting easting/northings

[Norm Olsen]

Hello Brian . . .

What you desire to achieve will be very tricky.

While you know the projection used, you probably don't know the projection parameters.  You will need to make a guess.  I suggest that you use the Lambert Conformal Conic 1SP.  Choose an origin longitude and latitude which roughly approximate the center of the map, probably someplace in Kansas.  You will then need to estimate the X and Y pixel values the correspond to your chosen origin.  These pixel values become you false easting and false northing.  Finally, you will need to arbitrarily choose a linear unit for your system, say meters.  This is not too important.

What is important, and will be tricky to determine, is the scale factor to use.  You will essentially need to enter a value which approximates the conversion of your chosen system unit (i.e. meters) to pixels.  As you image is 400x300, your scale factor will be a pretty small number.  That is, assuming with the padding the real world distance from the left edge of the image to the right edge is 4,000 miles (~6.44 million meters), your scale factor (i.e. the scale reduction factor) would probably need to be in the 6.0E-05 range. 

I suspect that most coordinate conversion packages will not accept a scale reduction factor that small.  So you will probably need to go with 1.0 as the scale reduction factor and apply the 6.0E-05 scale factor externally.

Best of luck to you.

Norm
--
Norm Olsen
Software Engineer
Autodesk, Inc.
303-277-9967

-----Original Message-----
From: metacrs-bounces at lists.osgeo.org [mailto:metacrs-bounces at lists.osgeo.org] On Behalf Of Brian Lewis
Sent: Thursday, February 24, 2011 7:46 PM
To: metacrs at lists.osgeo.org
Subject: [MetaCRS] plotting easting/northings

I have a 400x300 image taken from a map made using Lambert Conformal
Conic projection. The image is of the United States with some padding,
approximately 140W..50W, 20N..60N.

I want to plot some points of interest on the image. I convert the
latitude/longitude pairs to LCC easting/northings. But I can't figure
out how to relate the easting/northings to x/y in the image.

Any help would be greatly appreciated.
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