Bipolar Oblique Conformal Conic

[RustyRex]

I am looking for the projection used in an old 1975 geologic map.  After looking at Snyder's 'Map Projections of USGS' document, I think it may have been drafted in Bipolar Oblique Conic Conformal.  Esri says it supports this projection but I dont see it in the list of projections when I select custom.  Anyone have any ideas?

[MelitaKennedy · Accepted solution]

Hi Rusty,

It's supported in ArcInfo workstation only (like the doc says) so it would work with coverages and grids. It has, honestly, a flaky algorithm that we would want to significantly rework if/when it was put in the projection engine used by ArcGIS for Desktop/Server/etc. As the Limitations say:

The bipolar oblique conformal conic projection will display North America and South America only. If having problems, check all feature types (particularly annotation and tics) and remove any features that are beyond the range of the projection.

I can remember one coverage that has a tic in the mid-Atlantic, the projection algorithm couldn't handle it.

It's only been asked about every few years, so working on it has never made it high enough in our to-do lists.

Melita

[RustyRex]

Thanks for the reply.  Do you have a recommendation for something that projects North America similarly?  I want to georeference the old map in something close to reduce amount of warping and number control points needed.

Thanks,

[MelitaKennedy]

That's a very interesting question!

We don't have an oblique version of the Lambert conformal conic which would be the best match. My next thought was possibly Hotine oblique Mercator or rectified skew orthomorphic (same but latter has a rectifying angle parameter). My next thought was to try the Krovak projection. It's an oblique conic, conformal that was designed for Czechoslovakia and is still used in the Czech Republic. The parameters are a bit of a mess, but I quickly threw together some that, to my eye, look like it's approaching (very roughly!) the picture in Snyder's Map Projections: A Working Manual on page 121.

bipolar_equivalent
Authority: Custom

Projection: Krovak
False_Easting: 0.0
False_Northing: 0.0
Pseudo_Standard_Parallel_1: 30.0
Scale_Factor: 1.0
Azimuth: 50.0
Longitude_Of_Center: -20.0
Latitude_Of_Center: 45.0
X_Scale: -1.0
Y_Scale: 1.0
XY_Plane_Rotation: 90.0
Linear Unit: Meter (1.0)

Geographic Coordinate System: GCS_Sphere_ARC_INFO
Angular Unit: Degree (0.0174532925199433)
Prime Meridian: Greenwich (0.0)
Datum: D_Sphere_ARC_INFO
  Spheroid: Sphere_ARC_INFO
    Semimajor Axis: 6370997.0
    Semiminor Axis: 6370997.0
    Inverse Flattening: 0.0

Don't pay too much attention to the GCS. Snyder says that a sphere was used, but doesn't say which one. If the data/map does, you should use that information. A sphere with a radius of 6370997.0 is approximate the authalic sphere for Clarke 1866 (same surface area).

Melita

[RustyRex]

Thanks for your help.  Ill try it out.

I leave you with this: