Point Sample

The Grids | Calculate | Point Sample command computes the interpolated Z value on a gridded surface at given XY locations. XY locations from a data file are used to sample the grid. Bilinear interpolation is used to calculate the Z value at the XY location from the nearest four grid nodes. If a Z value cannot be calculated due to NoData nodes or if the XY location is beyond the extent of the grid, the cell is left blank in the output worksheet.

 

A worksheet window is automatically opened after the Point Sample command is used. The worksheet includes the data file used for the calculation and the newly generated point sample information. Use the worksheet's Data | Data | Statistics command to obtain statistical information on the calculated Z values.

 

After clicking OK in the Point Sample dialog, the worksheet window opens with the original data and the new Grid Value column.

 

Point Sample Dialog

Click the Grids | Calculate | Point Sample command to open the Point Sample dialog.

 

Specify the grid, XY data, and the column for the sampled points in the Point Sample dialog.

 

Input Grid

Specify the source map layer or grid file in the Input Grid section. Click the current selection and select a map layer from the list. Only map layers created from grid files are included in the Input Grid list. Click Browse to load a grid file with the Open Grid dialog.

 

XY Data

Specify the data file in the XY Data section. Click the current selection and select a map layer from the list. Only post and classed post layers are displayed in the XY Data list. Click Browse to load a data file with the Open Data dialog.

 

Data Columns

Specify the location for the X and Y coordinates from the data file in the Data Columns section.

 

Store Z values in Column

In the Store Z values in column box, enter the column where you would like the sampled Z values stored. By default, Surfer selects the first empty column in the data file.

 

 

See Also

Calculating the Agreement between a Grid and the Original Data File

Calculating the Value of the Surface at a Point

Residuals

Grids Tab Commands