----------------------------Original message----------------------------
On Thu, 6 Jul 1995, Art Lassagne wrote:
> ----------------------------Original message----------------------------
> The author of the AniMap County Boundary Historical Atlas is working on a
> Canadian version to show county, district and other subprovincial boundaries.
> One of the features we want to include is tracking the latitude/longitude
> position of the cursor as we have now done with the U.S. maps.
>
> His question is: "Where can one find the mathematical equations needed to
> translate (or 'deproject') an Albers Equal Area projection to rectilinear
> coordinates?"
>
>
Since this seems to be 'the answer' to 'how is projection type "x" done' and
includes scale type and eccentricity type it is quite complete.
Don't just 'snip the code' and stick it in your programs, get permission
first or just see how it was done and create NEW source code yourself.
Try:
file://nmdpow9.er.usgs.gov/public/gctpc
In the directory there is '.C' source code for a program that displays
map data, it includes the math for dealing with mapping.
Available projection transformations:
GEO (Geographic), UTM (Universal Transverse Mercator), SPCS (State Plane
Coordinates), ALBERS (Albers Conical Equal Area), LAMCC (Lambert Conformal
Conic), MERCAT (Mercator), PS (Polar Stereographic), POLYC (Polyconic),
EQUIDC (Equidistant Conic), TM (Transverse Mercator), STEREO (Stereographic),
LAMAZ (Lambert Azimuthal Equal Area), AZMEQD (Azimuthal Equidistant),
GNOMON (Gnomonic), ORTHO (Orthographic), GVNSP (General Vertical Near-Side
Perspective), SNSOID (Sinusoidal), EQRECT (Equirectangular), MILLER (Miller
Cylindrical), VGRINT (Van der Grinten), HOM (Hotine Oblique Mercator--HOM),
ROBIN (Robinson), SOM (Space Oblique Mercator--SOM), ALASKA (Modified
Stereographic Conformal--Alaska), GOOD (Interrupted Goode Homolosine),
MOLL (Mollweide), IMOLL (Interrupted Mollweide), HAMMER (Hammer),
WAGIV (Wagner IV), WAGVII (Wagner VII), OBLEQA (Oblated Equal Area).
Unit code for coordinates. Valid unit codes are:
radians, U.S. feet, meters, seconds of arc, degrees of arc, International feet
or a table supplying the unit code, which is legislated for the State
zone selected
This identifies the semi-major axis and eccentricity that is to be
used in the transformation process:
Clarke 1866 (default), Clarke 1880, Bessel, International 1967,
International 1909, WGS 72, Everest, WGS 66, GRS 1980/WGS 84, Airy,
Modified Everest, Modified Airy, Walbeck, Southeast Asia, Australian
National, Krassovsky, Hough, Mercury 1960, Modified Mercury 1968, Sphere
of Radius 6370997 meters,
Robert Clark
[log in to unmask] UNIX(r) System V Release 4.0 [142.103.106.2]
http://www.freenet.vancouver.bc.ca incoming:// 49 15 00 N 123 07 00 W
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