Custom (Coordinate Systems) tab

  

Petra contains two ways of selecting a coordinate system:  Custom and Standard. Both set a new project's coordinate system and also re-project an entire project to use a different coordinate system (provided the reference datum stays the same).  

Most commonly, the Custom coordinate system provides backwards compatibility for Petra projects older than October 2008.  Older projects with Custom coordinate systems can either be left alone, or easily converted into the analogous Standard coordinate system.

Custom coordinate systems are also useful for handling obscure coordinate systems not included in the Standard coordinate system list.  Additionally, a custom coordinate system can create a unique and highly accurate map projection for a small area.  It is important to note, however, that XY locations based on a custom map projection will not be compatible with XYs from standard map projections such as state planes.  This can cause difficulty in giving XY locations to drillers, for example.

The Custom tab can create and modify coordinate systems in three ways: creating a coordinate system from scratch, modifying an existing coordinate system, or creating a coordinate system based on data limits.

Projection tab

The Projection tab sets the specifics of the map projection.

  • Central Meridian - Sets the longitude of the center of the map projection.
  • Latitude of Origin - Sets the latitude of the center of the map projection
  • Northern Reference Latitude - Sets the northern reference latitude.
  • Southern Reference Latitude - Sets the southern reference latitude.
  • Scale Factor at Origin - The scale factor is the ratio between distances in the projection and distances on the surface of the reference ellipsoid.  This option sets the scale factor at the origin.
  • False Northing (Meters) - Specifies the Northing/Y coordinate at the origin of the projection.
  • False Easting (Meters) - Specifies the Easting/X coordinate at the origin of the projection.

Elipsoid tab

The Ellipsoid tab selects the ellipsoid (spheroid) model to use with the projection. The semi-major axis and inverse of the flattening are displayed. Please note that ellipsoids are not used in XY mode.

Petra stores its ellipsoid parameters in Ellipsoid.DAT, located in the installation's PARMS subdirectory. This file can be modified if extreme care is taken to maintain the format integrity.

State Plane tab

Petra stores its ellipsoid parameters in Ellipsoid.DAT, located in the installation's PARMS subdirectory. This file can be modified if extreme care is taken to maintain the format integrity.

Coord Sys tab

Contains several coordinate systems from China and Israel.  To use one of these coordinate systems, select one from the list and click the 'Apply' button.

Selecting a projection for a custom coordinate system

After entering all criteria ClickSave to enact the changes.  For new projects this will simply set the project's map projection.   For existing projects, saving a different coordinate system means that the XYs of all the data will need to change as well.

Changing the coordinate system changes the XY positions of wells.  Select "Yes" to recompute the positions in the database.

Make sure to select Yes when Petra asks to recompute XY well locations using the new map projection.

Related Topics

Modifying an Existing Coordinate System

Creating a Coordinate System from Scratch

Creating a Coordinate System Set by Data Limits