Defining a new projection

New projections are stored in a userproj.txt file that can be stored either locally, in the $PROHOME/etc folder, or both.

You can add a new projection to the system by modifying userproj.txt using a text editor to add the parameters for the projection. A template of the supported fields is included in userproj.txt, which you will find in the comment lines at the top of the file.

! User-defined projections
!
! NOTE: Comments follow an exclamation mark ('!').
!
! Fields supported for all User Defined Projections:
! ProjectionName        "11_char_max"
! ProjectionDescription "projection description (1 line of text)"
! ProjectionCountry     "country projection used in (1 line of text)"
! MapUnits              "PCI MAPUNITS (16_char_max)"
!
! Any of the map projections (except "LONG/LAT") 
! can have their units defaulted (normally this will be "METRE")
! or can have the ground units specified as one of the following:
! Units                 "FOOT"     ! that is, U.S. Survey Feet
! Units                 "INT FOOT" ! that is, International Feet
! Units                 "METRE"    ! or meters
!
! Fields supported dependant on the real projection defined in MapUnits:
! TrueOriginLongitude
! TrueOriginLatitude
! 1stStandardParallel
! 2ndStandardParallel
! FalseEasting
! FalseNorthing
! Scale
! Point1Longitude
! Point1Latitude
! Point2Longitude
! Point2Latitude
! Azimuth
! LandsatNumber
! LandsatPath

ProjectionName        "UKNatGrid"
ProjectionDescription "British National Grid (Transverse Mercator)"
ProjectionCountry     "Great Britain"
MapUnits              "TM D131"
TrueOriginLongitude    2dW
TrueOriginLatitude    49dN
Scale                 0.9996012717
FalseEasting           400000
FalseNorthing         -100000		
...

When working with new projects, the following rules apply:

• Each non-comment line consists of a field identifier (for example, ProjectionName) and a value for the field (for example, UKNatGrid). One or more spaces separate the field identifier and the field value. The field identifier and value must fit on one line. Although the present user projection examples have the field identifier first followed by the field value, the field value followed by the field identifier is also supported.
• Processing for the field identifiers is not case-sensitive.
• Blank lines are acceptable in the file and are ignored.
• If a field value contains spaces, it must be enclosed in double quotation marks ("); for example, ProjectionDescription "British National Grid".
• Comments follow an exclamation mark. If a line begins with an exclamation mark, the entire line is a comment. Trailing comments in a given line are acceptable.
• Processing for a given projection begins when a "ProjectionName" record is read and ends with the next "ProjectionName" record, or when the end of the file is reached. The order of the other records for the projection does not matter.

• Different projections require different parameters. The following fields can be defined for any user-defined projection set:

  • ProjectionName: The user-defined name that is presented for the projection set. This can be a maximum of 11 printable characters. For example, ProjectionName "UKNatGrid".
  • ProjectionDescription: The descriptive text that is presented with the ProjectionName. Although there is no maximum size, the ProjectionDescription must be short and a maximum of 64 characters. Spaces in the description must be enclosed in double quotation marks ("); for example, ProjectionDescription "British National Grid".
  • MapUnits: The actual units of the projection set that correspond to the units string that is built by using the "Generic Projections". This can be a maximum of 16 characters; for example, you can use either MapUnits "tm e9" or MapUnits "TM E009".