Transformations

You transform point coordinates using Cogo transformations or local transformations.

Cogo transformations

Use a Cogo transformation to transform a single point, or a selection of points, using one or a combination of rotation, scale or translation.

A Cogo transformation deletes the original point(s) and stores new grid points of the same name.

Local transformations

Use a local transformation to transform Grid (local) points to Grid points.

Local transformation support is available only when the Advanced Geodetic option is enabled in the Cogo settings screen of the job properties.

There are often occasions in surveying where existing points to be tied into or staked out have grid coordinates defined in one or more coordinate or reference systems, which are different from the current job's coordinate system. These other coordinate or reference systems may be defined based on old base lines where the coordinates are effectively station and offset values from the base (reference) line. Or they may be referenced to a completely arbitrary reference system. For example, an architect may provide coordinates for a building foundation that needs to be positioned and transferred into a real coordinate system on site.

Unlike a Cogo transformation, a local transformation does not change the coordinates of the original points. Instead, points can be created as Grid (local), and a relationship to Grid is defined that provides the transformation to the local coordinate system.

Grid (local) points cannot be displayed in the map if a transformation to grid has not been defined.

Trimble Access lets you compute and store one or more local transformations that will transform on‑the‑fly between the grid coordinates and sets of local grid coordinates. Transformations can be applied and used when:

  • Keying in points
  • Linking files to the job
  • Staking out points from a linked CSV or TXT file
  • Reviewing the job
  • In Point manager
  • Importing a comma delimited file
  • Exporting as Grid (local)

A point stored as a Grid (local) can only ever have one 'input' transformation that defines the relationship to database Grid positions. However, when viewing with Review job or Point manager, and when exporting as Grid (local), you can select a different local transformation, which changes the displayed computed Grid (local) coordinates.

You can, for example, key in a Grid (local) point referenced to one baseline or reference system, and transform to the database grid, and then, if required, use another 'display' transformation to display the point with computed Grid (local) values referenced to a different baseline or reference system. This is analogous to how any point can be displayed as station and offset to any line, arc, alignment, or road.

 

  • To select a different input transformation, use Point manager.
  • To copy transformations to other jobs, use Copy between jobs.

In Trimble Access you can create and apply the following types of local grid transformation:

  • The Line transformation type is a 2D transformation that allows you to select or key in two database grid points and match them up with the local grid coordinates for the same positions.
  • The Helmert transformation type can be a 2D Helmert transformation or a 3D transformation performed as a 2D Helmert transformation and a 1D inclined plane transformation. You can select up to 20 identical point pairs to compute a best fit transformation between the database grid points and the local grid coordinates for the same positions.

  • The Seven parameter transformation type is a 3D transformation that allows you to select up to 20 identical point pairs to compute a best fit transformation between the database grid points and the local grid coordinates for the same positions.

    A Seven parameter transformation will provide a better solution than a Helmert transformation if the two coordinate systems are not defined with respect to the same horizontal plane.