By selecting this section the coordinate operation will correct the input coordinates based on some corrections (distortions) calculated by interpolation from a distortion grid.

Corrected coordinates type

Sign of corrections

It selects the sign that will be applied to the corrections: plus or minus.

This sign is used to choose the direction of the transformation. For the plus sign the calculated correction will be added to the value of the input coordinates and for the minus sign they will be deducted. At the inverse calculation (applying with the minus sign) the interpolation on the grid is made iteratively.

Interpolation method

It selects the interpolation method used to calculate the corrections: Bilinear, Bicubic spline, Biquadratic or No interpolation .

For the Bilinear method the interpolation is made using a single grid cell (4 nodes), the cell in which the point is found.

For the Bicubic spline method the interpolation is made using 3x3 cells from the grid (16 nodes), the cell from the middle being the one in which the point is found.

For the Biquadratic method the interpolation is done using 2x2 cells from the grid (9 nodes). The four cells are chosen so that the middle node is the closest to the point.

For the No Interpolation method the value applied is the one from the node closest to the point.

Time dependent

Contains velocity of movement

Choose whether or not the file contains point movement velocity.

Source epoch

Choose whether the grid has a defined source epoch and if so, enter the epoch value.

Target epoch

Choose whether the grid has a defined target epoch and if so, enter the epoch value.

Velocities type

Select the velocity type contained in the grid. Depending on the velocity type and the corrected coordinate type, a transformation of the velocity values from one system to another will be performed. If the corrected coordinate type is (X,Y,Z) and the velocities are expressed in (Vn,Ve,Vu) (North, East, Up velocities), they will be converted into geocentric cartesian coordinate velocities (Vx,Vy,Vz). Similarly, for corrected coordinates (φ,λ) or (φ,λ,h), if the velocities are expressed in (Vn,Ve,Vu), they are converted into coordinate velocities (Vφ,Vλ,Vh).

Unit of measurement (V)

Select the unit in which the displacement velocities (crustal/tectonic) are expressed inside the grid. Depending on the loaded grid type, the values can be: mm/yr (Millimeters per year) or mas/yr (Milliarcseconds of sexagesimal arc per year). The mas/yr unit applies only to geographic coordinates (φ,λ); for all other coordinate types, the mm/yr unit is used.

Note: The type of velocity and the unit of measurement are dependent on the type of corrected coordinates.

Reference datum

The grid reference datum is used when correcting geocentric coordinates (X,Y,Z), in which case a conversion to geographic coordinates (φ,λ) is required to identify the grid cell. It is also used when correcting geographic coordinates using a velocity grid, where it is necessary to convert linear displacements (e.g., from millimeters) into angular variations.

Ellipsoid short name

Set the short name of the ellipsoid.

Button Select ellipsoid...

Choose an ellipsoid from the list of predefined ellipsoids.

Semi-major axis

Set the value of the major semi-axis.

Inverse flattening

Set the value of the inverse flattening. To define a sphere, introduce the value 0.000.

Prime Meridian

Select the prime meridian of the used datum. If the prime meridian differs from Greenwich, the conversion from geographic coordinates (φ,λ,h) to Cartesian geocentric coordinates (X,Y,Z) is made always relative to the Greenwich zero meridian and for the inverse conversion the longitude calculated from (X,Y,Z) is rotated in order to return to the selected prime meridian.

Grid file

Button Select grid file ...

It opens the window where you select a grid type file.

Information about the type of files supported by the program can be found at Supported transformations and conversions - Table no.5 .

Note: We recommend that the grid files that you use to be copied in the Grids folder on the path where TransLT is installed (C:\Program Files\TransLT\Grids) because the grid files are searched in this folder. If not, the saved transformation model that contains a grid file with a path specific to the computer you are using will not be loadable on another computer.

Button Load values from the EPSG database

Ity opens The window of loading parameters from the EPSG database . The data taken from an operation with type Offset with grid file is: the type of corrected coordinates, the sign of applying the corrections (direction) and the name of the grid file.

Button Preview grid ...

It opens the View Grid Points window. For the type or corrected coordinates h and (φ, λ) the preview is 3D and for (N, E) the preview is 2D.

Button Show the grid file properties ...

It opens the window with the properties of the selected grid file. The following information is presented: file location, file size, file format, total number of grids, total number of nodes and contained grids. For the selected grids and subgrids are presented: number of rows, number of columns, number of nodes, minimum and maximum coordinates and step on the two directions.

Note: Only gsb files (Ntv2 format) support multiple grids, including subgrids.

List box with information about the selected grid file

In this list is presented general data about the selected grid file. Information is taken from "_About_grids.mdb" file that is in "Grids" folder on the path where the program is installed.

If you use grid files that are not put in the Grid Files Information table from mdb file, it is recommended to fill yourself the table with information about the new used grid files. You may send us the information about these files via email at the address support@3dspace.ro .