The most common projections for cones are listed below.

## Albers Equal-Area Conic

A very popular projection for maps of the continental United States and used extensively by the U.S. Geological Survey. Developed in 1805 by German native H. C. Albers and is an equal-area projection. It is especially suited for nations like the USA that are wider east/west than north/south. Parallels are concentric arcs of circles, not equally spaced. The meridians are equally spaced radii of the same circle, running at 90 degrees. Normally it is arranged with two standard parallels.

## Bipolar Conic

The full name is Bipolar Oblique Conic Conformal Projection. It was developed in 1941 by O. M. Miller and W.

A. Briesemeister in order to create new maps of North and South America and is an adaptation of the Lambert Conformal Conic projection. Bipolar Conic is a conformal projection made up of two oblique conic projections placed beside one another with poles 104 degrees apart. The parallels and meridians cross at right angles but are complex curves.

This projection is supported in the spherical form only.

## Equidistant Conic

The oldest and most straightforward of the Conic projections. It is also known as the Simple Conic or Conic and has been in use since Ptolemy developed it sometime around 150 A.D. The parallels are arcs of evenly spaced, concentric circles. The meridians cut across the parallels at right angles. Suitable for maps which extend east/west rather than north/south. It is still the projection of choice for many smaller nations.

This projection is also known as the Simple Conic Projection.

## Krovak

Known as the Czechoslovakian Krovak projection, this system is based on an implementation of the Oblique Conformal Conic projection

The prime meridian of Ferro (one of the Canary Islands) is the longitude of origin. The non-rounded location is at 17°39´59.7354W longitude, while the rounded location is 17°40´00.00W longitude. Both variations are supported.

## Krovak (Generalized)

Allows user to specify precise or rounded origin. JTSK option also supported.

## Lambert Conformal Conic

Another projection first developed in 1772 by Lambert. It is sometimes called the Conic Orthomorphic projection. Like the Albers Equal-Area Conic, the Lambert is well suited for areas with a mainly east-west expanse. It is the official projection for the SPCS for States with this geography. (The Transverse Mercator has the same status for States which run mainly North/South.) A number of aeronautical charts use the Lambert. The parallels are arcs of concentric circles, which become more closely spaced as they move toward the center of the map. The meridians run at right angles to the parallels. With two standard parallels, the area distortion is minimal between and near the standard parallels.

## Usage Notes

X, Y swapping can be accomplished by setting the Krovak parameter "quadrant = -1".

When transforming data from another projection, you may notice that the results appear to be rotated 90

degrees. This can be resolved by setting the Krovak parameter "quadrant = -1". Internally, X and Y are

swapped after the transformation and before elements are re-composed.

An example of these coordinate systems are provided in the "dgn" directory of this product.

Example dgns provided:

- � krovkG_aux.dgn - General-purpose Krovak
- � krovkP_aux.dgn - Precise Origin Krovak
- � krovkR_aux.dgn - Rounded Origin Krovak

## Lambert Conformal Conic (Belgian variation)

Identical to Lambert Conformal Conic, except mathematics are specific to the Belgian system. belgian constant = 29.2985 * (1.0 / 3600) * 0.01745329251994329577

## Lambert Conformal Conic (1 Standard Parallel variation)

This variation is commonly used outside of North America and is mathematically identical to Lambert Tangential.

This projection is virtually identical to the Lambert Conformal conic except that the two standard parallels are calculated as result of the specified scale reduction factor. A scale reduction factor of 1.0 produces two identical standard parallels.

## Lambert Tangential

Please use Lambert Conformal Conic 1 Standard Parallel variation instead of this one.

## Polyconic

Sometimes known as the American Polyconic, it was for a long time the standard projection for large scale maps of the United States. It was developed in 1819 by F. H. Hassler, the first Superintendent of the U.S. Coast Survey and used extensively until the 1950s. Created as a compromise between an equal-area and a conformal projection, the polyconic has low distortion along the central meridian. The Central meridian is projected as a straight line, while all other meridians are complex curves. Parallels are not concentric, they are arcs of circles. The Equator however is a straight line. In the USA, the polyconic has been replaced by the Transverse Mercator or Lambert Conformal Conic projections commonly associated with the State Plane Coordinate System.

## Modified Polyconic

Devised by the French cartographer Lallemand in order to allow the mapping of large areas with a polyconic projection. In 1909, the International Map Committee (IMC) began using it for its International Map of the World (IMW) series. It was replaced by the UN conference on the IMW in 1962.

## Bonne

Generally attributed to R. Bonne, the 18th century French geographer used this projection a great deal. Forms of it, however, have been in use for over 400 years. It was most often found in atlas maps of the continents. It is an equal area projection, with the central meridian forming a straight line while all others form complex curves. The parallels are concentric circular arcs.

In common use until the early part of this century, it is now less favored by atlas map makers, but still used in some European nations.

There are two limiting cases. If the origin latitude is either pole, this produces the Werner projection. Some special code is required to prevent divide by zero.

If the origin latitude is zero, the mathematics for this projection break down and the projection approaches the Sinusoidal.