CDT allows you to perform a multiple merging in a nested way, the outputs of the previous merging are used as input for the current merging process. Multiple passes are made through the grid at consecutively smaller radius of influence and number of neighbor stations used to increase precision. At each pass, the radius of influence, minimum and maximum number of neighboring stations used to interpolate on grid node are decreased in a given ratio. In other words, the parameters used for the local interpolation, maxdist, nmin and nmax will be multiplied by the factor provided by the user (Pass ratio). The table below shows an example summarizing the process of merging with 4 nested runs.
| Run number | Pass ratio example | maxdist | nmin | nmax | Input data | Output data |
|---|---|---|---|---|---|---|
| 1 | 1 | 4 | 8 | 16 | Initial input (E.g.: Bias adjusted rainfall gridded data) | Output 1 |
| 2 | 0.75 | 4 * 0.75 = 3 | 8 * 0.75 = 6 | 16 * 0.75 = 12 | Output 1 | Output 2 |
| 3 | 0.5 | 4 * 0.5 = 2 | 8 * 0.5 = 4 | 16 * 0.5 = 8 | Output 2 | Output 3 |
| 4 | 0.25 | 4 * 0.25 = 1 | 8 * 0.25 = 2 | 16 * 0.25 = 4 | Output 3 | Output 4 |
The final merged data is Output 4. Note that if the difference between nmax and nmin is less than 2, then 2 more neighbor stations will be added to nmax.