Latest revision as of 17:04, 19 August 2010

This page explains what is PROJ4 library and how to use it from the command line, in Windows and in Linux.

PROJ4 is an open-source Cartographic Projections library originally written by Gerald Evenden then of the USGS. This library has almost all projection types and it is very usefull to convert coordinates for a series of points.

It is written in C but a Fortran wrapper was developed as part of the GLIMMER project. More information can be found in libfproj4

Installation

Windows

• Download http://download.osgeo.org/proj/proj446_win32_bin.zip
• Extract and copy "proj" folder to C:\
• Right-click "My Computer" and select "Properties"
• Select "Advanced" tab
• Select "Environment Variables"
• In the "System Variables" box select "Path" and click "Edit".
• At the end of the line, add "C:\proj\bin" and click "OK".
• In the "System Variables" box, click "New".
• "Variable Name" is PROJ_LIB and "Variable Value" is "C:\proj\nad".
• Click OK to close windows.

Now test it:

• Windows/Run/cmd
• cd .. until prompt is C:\>
• write "proj -V" to see the version of the library.

Linux

• Go to your Package Manager or download source code from http://trac.osgeo.org/proj/ and follow the instructions.

Usage

The Proj4 is well documented. Here are some commands that I found useful.

Basic

degrees to meters (forward projection)

proj -f "%.2f" +proj=utm +zone=29 +ellps=WGS84
-7.1 38.2                                         (input)
666368.11       4229712.04                        (output)

meters to degrees (inverse projection)

proj -I -f "%.2f" +proj=utm +zone=29 +ellps=WGS84  
666368.11 4229712.04                                 (input)
-7.10   38.20                                        (output)

Portuguese Military Coordinates (Hayford-Gauss Military System)

• Projection: Gauss-Kruger
• Ellipsoid: Hayford (internacional 1924): a=6378.388Km, b=6356.912 Km
• Datum : Lisbon (Castelo S.Jorge: 38º42’43.631’’N, 9º07’54.862’'W, 111.229m)
• Central Point: 39º40’N, 8º07’54.862’’W
• Origin: -200Km horizontally and -300 Km vertically

proj -f "%.2f" +init=epsg:20790

or

proj -f "%.2f" +init=esri:102164

or

proj -f "%.2f" +proj=tmerc +lat_0=39.66666666666666 +lon_0=-8.131906111111112 +k=1.000000 
               +x_0=200000 +y_0=300000 +ellps=intl +pm=lisbon +units=m +no_defs  no_defs

Universal Transverse Mercator (zone 29N)

proj -f "%.2f" +init=esri:32629

or

proj -f "%.2f" +proj=utm +zone=29 +ellps=WGS84 +datum=WGS84 +units=m

List of projections

List of projections in PROJ4: proj -lp

List of ellipsoids

List of ellipsoids in PROJ4: proj -le

More popular:

• • International 1909 (Hayford) intl a=6378388.0m b=6356912m rf=297.
  • New International 1967 new_intl a=6378157.5m b=6356772m
  • WGS 84 WGS84 a=6378137.0m b=6357002m rf=298.257223563
  • Normal Sphere (r=6370997) sphere a=6370997.0m b=6370997m

b = a*(1-f) = a*(1-1/rf)

Portuguese Coordinate Systems in PROJ4

You might want to get the libraries containing the coordinate transformations with Portuguese datum pre-configured here. Install the libs in the proj_lib folder, inside the FWTools folder. By the way, you may want to install FWTools first.

Here's the command line on how to convert from military portuguese to wgs84:

 cs2cs +init=pt:dlxhgmil +to +init=pt:etrs89 < coords_input.txt

Internal Links

• libfproj4
• ConvertToHDF5

External Links

• PROJ4
• Sistemas Referencia Portugueses
• PROJ4_HandlingCoordinateSystems.pdf
• Projections and Projected Coordinate System Formulas