# Difference between revisions of "GMS:Subset Definition"

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In the IDW Interpolation Options dialog, an option is available for using a subset of the | [[File:SubsetDefinition.png|thumb|225 px|The ''Subset Definition'' dialog.]] | ||

In the [[GMS:Inverse Distance Weighted|''IDW Interpolation Options'']] dialog, an option is available for using a subset of the data points (as opposed to all of the available data points) in the computation of the nodal function coefficients and in the computation of the interpolation weights. Using a subset of the data points drops distant points from consideration since they are unlikely to have a large influence on the nodal function or on the interpolation weights. In addition, using a subset can speed up the computations since less points are involved. | |||

If the Use subset of points option is chosen, the Subsets button can be used to bring up the Subset Definition dialog. Two options are available for defining which points are included in the subset. In | If the ''Use subset of points'' option is chosen, the '''Subsets''' button can be used to bring up the ''Subset Definition'' dialog. Two options are available for defining which points are included in the subset. In the first approach, only the nearest ''N'' points are used. In the second approach, only the nearest ''N'' points in each quadrant are used as illustrated in the figure below. The second approach may give better results if the data points tend to be clustered. | ||

[[Image:idw_fig1. | :[[Image:idw_fig1.png|thumb|none|200 px|The four quadrants surrounding an interpolation point.]] | ||

==Related Topics== | |||

* [[GMS:Inverse Distance Weighted|Inverse Distance Weighted]] | |||

{{Navbox GMS}} | {{Navbox GMS}} | ||

[[Category:Interpolation]] | [[Category:Interpolation]] | ||

[[Category:Interpolation Dialogs]] | |||

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## Latest revision as of 20:20, 28 March 2017

In the *IDW Interpolation Options* dialog, an option is available for using a subset of the data points (as opposed to all of the available data points) in the computation of the nodal function coefficients and in the computation of the interpolation weights. Using a subset of the data points drops distant points from consideration since they are unlikely to have a large influence on the nodal function or on the interpolation weights. In addition, using a subset can speed up the computations since less points are involved.

If the *Use subset of points* option is chosen, the **Subsets** button can be used to bring up the *Subset Definition* dialog. Two options are available for defining which points are included in the subset. In the first approach, only the nearest *N* points are used. In the second approach, only the nearest *N* points in each quadrant are used as illustrated in the figure below. The second approach may give better results if the data points tend to be clustered.

## Related Topics

GMS – Groundwater Modeling System | ||
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Modules: | 2D Grid • 2D Mesh • 2D Scatter Point • 3D Grid • 3D Mesh • 3D Scatter Point • Boreholes • GIS • Map • Solid • TINs • UGrids | |

Models: | FEFLOW • FEMWATER • MODAEM • MODFLOW • MODPATH • mod-PATH3DU • MT3DMS • MT3D-USGS • PEST • PHT3D • RT3D • SEAM3D • SEAWAT • SEEP2D • T-PROGS • ZONEBUDGET | |

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