Oblique Mercator

Classification: Conformal cylindrical

Available forms: Forward and inverse, spherical and ellipsoidal

Defined area: Global, but reasonably accurate only within 15 degrees of the oblique central line

Alias: omerc

Domain: 2D

Input type: Geodetic coordinates

Output type: Projected coordinates

Projection String

+proj=omerc +lat_1=45 +lat_2=55
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Required Parameters

• +lat_1=<value>: Latitude of the first point on the central line.
• +lat_2=<value>: Latitude of the second point on the central line.

Optional Parameters

• +alpha=<value>: Azimuth of the centerline clockwise from north at the center point of the line.
• +gamma=<value>: Azimuth of the centerline clockwise from north of the rectified bearing of the centerline.
• +lonc=<value>: Longitude of the projection center (overrides +lon_0).
• +lat_0=<value>: Latitude of the projection center.
• +no_rot: Disables rectification (historical reason).
• +no_off: Disables origin offset to the center of projection.
• +k_0=<value>: Scale factor at the central line.
• +x_0=<value>: False easting.
• +y_0=<value>: False northing.

Usage Example

echo 12 55 | proj +proj=omerc +alpha=90 +ellps=GRS80
echo 12 55 | proj +proj=omerc +alpha=0 +R=6400000
echo 12 55 | proj +proj=omerc +lon_1=0 +lat_1=-1 +lon_2=0 +lat_2=0 +R=6400000
echo 12 55 | proj +proj=tmerc +R=6400000
echo 12 55 | proj +proj=omerc +lon_1=-1 +lat_1=1 +lon_2=0 +lat_2=0 +ellps=GRS80
echo 10.536498003 56.229892362 | cs2cs +proj=longlat +ellps=GRS80 +to +proj=omerc +axis=wnu +lonc=9.46 +lat_0=56.13333333 +x_0=-266906.229 +y_0=189617.957 +k=0.9999537 +alpha=-0.76324 +gamma=0 +ellps=GRS80
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Caveats

The two-point method with no rectification is probably only marginally useful.