A spatial interpolation is the estimation of the unknown value of a point by using the measured points in the study area. To interpolate a spatial points data (stations observation) into gridded data, use the menu Gridding ‣ Spatial Interpolation  . It displays a tabbed widget on the left panel, allows to enter the inputs data, set the interpolation parameters and display maps of the interpolated data.



The tab   Input Data     allows to specify the input station data and the interpolation parameters.




  1. Select the temporal resolution of the input data in CDT stations data format. The available temporal resolution are: minutes, hourly, daily, pentad, dekadal, monthly data and others (seasonal, annual, …).

  2. In case of minutes and hourly, select here the time step of the input data.

  3. Select the CDT station data to interpolate with the drop down list if it is already loaded, or open it through   …  .

  4. Set the start and end date of the period to interpolate. See setting date range for more details.

  5. Click on the button   Interpolation Parameters   to set the parameters to be used to interpolate the station data. It opens a dialog box.

    CDT has 7 spatial interpolation methods: Inverse Distance Weighted, Ordinary Kriging, Universal Kriging, Modified Shepard interpolation, Spheremap interpolation method, Nearest Neighbor and Nearest Neighbor with elevation - 3D.

    By default CDT uses a local interpolation technique, therefore, you have to provide the minimum and maximum number of stations used to interpolate a grid point, and the maximum distance within which the stations are selected. See the spatial interpolation methods for further details, and the interpolation dialog to select the method to be used and set the interpolation parameters.

  6. Click on the button   Create Grid for Interpolation   to provide the grid to be used to interpolate the data. It will display the grid creation dialog box.

  7. In the case where the variable to be interpolated cannot be negative or below a certain value, check   Change negative values to    , enter the value you want to change the negative values in the activated input field.

  8. To mask the grid outside a given polygons, check   Blank grid outside the Shapefile    , this will activate the drop down list below allowing you to provide the Shapefile to be used. See the blanking options to control the buffer outside the polygons.

  9. Specify the folder to save the output by browsing it from the button or typing the full path to the folder.

When you finish to set everything in this tab, click on the button      Interpolate      to start the interpolation process.

This creates a folder named INTEPORLATION_<file name of station data> under the folder you provided (9) to save the outputs. Inside this folder 2 directories and 1 file are created:



The tab   Maps     allows to display the maps of the interpolated data.




  1. If you have already performed the interpolation before and you want to display the maps of the interpolated data,
    check   Data already computed    , this will activated the button   Load Data   allowing you to load the index file of the interpolated data. Browse the file SpatialInterpolation.rds via the open dialog box.

  2. Enter the date you want to plot in the input fields then click the button      PLOT      to display the map. You can use the button     <<     to display the map of the previous interpolated data and     >>     for the next date.

  3. Select the way the map will be displayed, in one panel or a separate panels.

one panel separate panels

  1. Select the type of map to display for the stations data, available options are Points and Pixels. See the type of plot for station data.

  2. Select the type of map to display for the gridded data, available options are Pixels and FilledContour. See the type of plot for gridded data.

  3. Click on the button     Options     to change the color bar, title and labels of the maps. For more details on how to change the options, see map options.