# [OSRS-PROJ] projection formula?

Chris Jessee cj8n at virginia.edu
Wed Oct 22 11:55:37 EDT 2003

```Hi,

I'm involved in a project that aims to offer an online tool with basic
GIS functionality as follows:

User mouse movement gives realtime lat lon readout.
A measure tool provides distance and angle measure between two points.
Point coverage can be loaded from external DB and plotted to a graphic
base map.

The tool will be built in Macromedia Flash. Implementing these features
on a geographic coordinate system is relatively easy as this demo shows.
http://jefferson.village.virginia.edu/salem/maps/
click the map on the left.
Flash player plug-in required.
We ruled out many off the shelf products due to poor visual quality.

The trouble begins when we try to use a base map in a
Lambert_Conformal_Conic projection. The specifics of the projection are
at the end of this email. To implement the functionality noted above I
have 2 choices: re-project the map into a Geographic Coordinate system
or dynamically calculate the difference between rectilinear screen
space and the conic projection. On the first option I'm also
considering a Platte Carre or Equidistant Cylindrical projection as
this should be easier to plot lat lon. Any thoughts on what a
appropriate Geographic Coordinate system might be to minimize visual
difference with Lambert_Conformal_Conic? On the second option, can
anyone point to a resource for formulas to convert
Lambert_Conformal_Conic to Platte Carre or GCS_North_American_1983?
I'll need the formula's since it all has to be implemented inside Flash
to get the user realtime feedback.

Coordinate system specifics

Lambert_Conformal_Conic
False_Easting: 200000.000000
False_Northing: 750000.000000
Central_Meridian: -71.500000
Standard_Parallel_1: 41.716667
Standard_Parallel_2: 42.683333
Latitude_Of_Origin: 41.000000

GCS_North_American_1983
Datum: D_North_American_1983
Prime Meridian: 0
Datum: D_North_American_1983
spheriod: grs 1980
semimajor axis 6378137
semiminor axis 6356752.3141403561
angular unit: degree
prime meridian: Greenwich

Thank you,

Chris Jessee
jessee at virginia.edu

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