Today I want to introduce **as3-proj**, an actionscript port of the java map projection library by Jerry Huxtable, which is itself an partial port of the PROJ.4 library. It’s basically a huge set of over sixty map projection classes which you can use to convert geographical coodinates (pairs of latitude and longitude values) into screen coordinates.

### Usage example

You can use the projection classes like this:

var lat:Number, lng:Number, proj:Projection, p:Point; lat = 40.2302; // degrees lng = 24.32434; // degrees proj = new RobinsonProjection(); proj->initialize(); p = proj->project(lat, lng, new Point()); // p contains converted values in metres

### Demonstration

I built a sample application that shows static world maps in different map projection. You can switch the map projection using the menu at the bottom. Also you can filter out some map projections, e.g. to only display rectilinear map projections. The visualization of some projections (like the Orthographic Projection) still need a little more coding to be perfect (eg. removal of hidden lines and faces), but this was out of the scope of this demo.

### Supported projections

You find a alphabetically sorted list of all included map projections and their properties below.

projection | has invers | parallels are parallels | is rectilinear | is conformal | is equal area |
---|---|---|---|---|---|

Airy’s Minimum-Error Azimuthal | no | no | no | no | no |

Aitoff | no | no | no | no | no |

Albers Equal Area | yes | no | no | yes | yes |

Boggs Eumorphic | no | yes | no | no | yes |

Bonne | yes | no | no | no | yes |

Cassini | yes | no | no | no | no |

Central Cylindrical | yes | yes | yes | yes | no |

Collignon | yes | yes | no | no | yes |

Craster Parabolic (Putnins P4) | yes | no | no | no | yes |

Cylindrical Equal Area | yes | yes | yes | yes | no |

Denoyer Semi-elliptical | no | yes | no | no | no |

Eckert I | yes | yes | no | no | no |

Eckert II | yes | yes | no | no | no |

Eckert IV | yes | yes | no | no | no |

Eckert V | yes | yes | no | no | no |

Euler | yes | no | no | yes | no |

Fahey | yes | yes | no | no | no |

Foucaut Sinusoidal | yes | yes | yes | yes | no |

Gall Stereographic | yes | yes | yes | yes | no |

Gall-Peters | yes | yes | yes | yes | yes |

projection | has invers | parallels are parallels | is rectilinear | is conformal | is equal area |

Ginsburg VIII (TsNIIGAiK) | no | yes | no | no | no |

Goode Homolosine | yes | yes | no | no | yes |

Hammer & Eckert-Greifendorff | no | no | no | no | yes |

Hatano Asymmetrical Equal Area | yes | yes | no | no | no |

Kavraisky V | yes | yes | no | no | yes |

Lagrange | no | no | no | yes | no |

Lambert Conformal Conic | yes | no | no | yes | no |

Lambert Equal Area Conic | yes | no | no | yes | yes |

Landsat | no | no | no | no | no |

Larrivée | no | no | no | no | no |

Laskowski Tri-Optimal | no | no | no | no | no |

Loximuthal | yes | yes | no | no | no |

McBride-Thomas Flat-Polar Parabolic | yes | yes | no | no | no |

McBryde-Thomas Flat-Polar Quartic | yes | yes | no | no | no |

McBryde-Thomas Flat-Polar Sine I | yes | yes | no | no | no |

McBryde-Thomas Flat-Polar Sine II | yes | yes | no | no | no |

Mercator | yes | yes | yes | yes | no |

Miller Cylindrical | yes | yes | yes | yes | no |

Mollweide | yes | yes | no | no | yes |

Murdoch I | yes | no | no | yes | no |

projection | has invers | parallels are parallels | is rectilinear | is conformal | is equal area |

Murdoch II | yes | no | no | yes | no |

Murdoch III | yes | no | no | yes | no |

Nell | yes | yes | no | no | yes |

Nell-Hammer | yes | yes | no | no | no |

Nicolosi Globular | no | no | no | no | no |

Orthographic Azimuthal | yes | no | no | no | no |

Perspective Conic | yes | no | no | yes | no |

Plate Carrée | yes | yes | yes | yes | no |

Putnins P’4 | yes | yes | no | no | yes |

Putnins P’5 | yes | no | no | no | no |

Craster Parabolic (Putnins P4) | yes | no | no | no | yes |

Putnins P5 | yes | no | no | no | no |

Quartic Authalic | yes | yes | no | no | yes |

Robinson | yes | yes | no | no | no |

Sinusoidal | yes | yes | no | no | no |

Transverse Central Cylindrical | no | no | no | no | no |

Transverse Cylindrical Equal Area | yes | no | no | no | yes |

Tissot | yes | no | no | yes | no |

Urmaev Flat-Polar Sinusoidal | yes | no | no | no | no |

van der Grinten (I) | yes | no | no | no | no |

projection | has invers | parallels are parallels | is rectilinear | is conformal | is equal area |

Vitkovsky | yes | no | no | yes | no |

Wagner II | yes | no | no | no | no |

Wagner III | yes | yes | no | no | no |

Wagner IV | yes | yes | no | no | no |

Wagner V | yes | yes | no | no | no |

Wagner VII | no | no | no | no | yes |

Werenskiold I | yes | yes | no | no | yes |

Winkel Tripel | no | no | no | no | no |

The following projection are also included but are a bit buggy yet. Maybe someone with more knowledge about map projection math is able to stop those formulas from throwing weird exceptions.

projection | has invers | parallels are parallels | is rectilinear | is conformal | is equal area |
---|---|---|---|---|---|

August Epicycloidal | no | no | no | yes | no |

Bipolar Conic | yes | no | no | no | no |

Equidistant Azimuthal | yes | no | no | no | no |

Lambert Equal Area Azimuthal | yes | no | no | no | yes |

Space-oblique Mercator | yes | no | no | no | no |

Since I only tested the one-way projection of geographic coordinates into screen coordinates there still might be some bugs on the inverse projections. The java code of the map projection library had a few errors. Hope the classes are helpful anyway.

### Download & License

The source code of as3-proj is released under the Apache License.

If my work is useful to you, please feel free to donate an amount of your choice via paypal. Thanks!

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I use Proj4 libray in my C++ project, when i try to use this AS3 version i found some projection types were removed, like Transverse Mercator, any ideas about this?

Thanks

Chen

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I was getting incorrect values from your Robinson Projection so I wrote my own and open sourced the code at:

http://www.flashmap.org/robinson-projection-in-as3-gpl/

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Gregor,

Thanks for the quick response and link to the tutorial. I ended up writing my own Robinson projection function in AS3 which it looks like was a duplication of work but definitely helped make me more familiar with what was going on.

Chris

Hi Chris,

Yoh have to multiply every projected y-coordinate by -1 before drawing. Assumedly the projection fomulas weren’t designed for screen output but for print output and thus refer to a mirrored coordinate system.

The tutorial I mentioned is already there, you can find it here.

Thanks for your work on this! I’m working with the Robinson projection and I’m confused why the sign of the X/Y coordinates differ from the sign of latitude and longitude. For example:

(-180,90)= (log,lat) in RobinsonProjection

(x=-125066398.48278639, y=-751566.9221849588)

Aren’t the X/Y coordinates also starting from an origin at the central meridian and the equator? Shouldn’t the sign for y and latitude be the same?

Also…if you get the chance to post that tutorial it’d be a life saver here too.

Thank you Gregor.

I still can’t work around how is it done?. A short tutorial would be really my life savior.

I use the DataView class. The constructor takes two rectangles. The first is the bounding box of all projected points (you have to iterate over all projected coordinates and store the minimum and maximum values of x and y). The second rectangle is your target screen area. By the way, I’ll publish a short tutorial showing this procedure in the next few days..

regards,

Gregor

Hi Thanks for porting PROJ.4 to as3.

For eg

(-180,90)= (log,lat) in RobinsonProjection

(x=-125066398.48278639, y=-751566.9221849588)

How can you I convert this X Y mapping coordinate to X Y pixel coordinate for Image (3600×1800 pixels)?

Thank you again for your time and effort.