GMS:Error Summary Plot
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An Error Summary plot is one of the plot types that can be created by the Plot Wizard. See the Error Summary plot section on the Plot Wizard page for a basic description. The Error Summary plot is used to display a text listing of the mean error, mean absolute error, and root mean squared error for an observation measurement in a coverage. The error values may be listed for a single time step of a dataset or for all time steps.
Contents
Error types
- Mean Error: This is the average error for the points. This value can be misleading since positive and negative errors can cancel.
- Mean Absolute Average: This is the mean of the absolute values of the errors. It is a true mean, not allowing positive and negative errors to cancel.
- Root Mean Square: This takes the average of the square of the errors and then takes its square root. This norm tends to give more weight to cases where a few extreme error values exist.
Time matching
When the measurement is transient (i.e., observed heads at various times) then it is very unlikely that the output times from the model match the times when the field measurements were taken. In this case GMS will interpolate an observed value at the model output time. If the model output time is before the first field measurement for a particular point then the interpolated value is the first measurement. Similarly if the model output time is after the last field measurement then the interpolated value is the last measurement. When the model output time is between the first and last measurement then GMS will find the 2 closest field measurments to the model output time and use linear interpolation to compute the "observed" value at that time.
MODFLOW errors
The Error Summary Plot is most useful with models that do not make error computations from observation data. MODFLOW does compute error computations from observation data, and these errors are available in the MODFLOW properties dialog. Therefore, when using MODFLOW, you should use the MODFLOW properties dialog and not the Error Summary Plot. The errors shown in the Error Summary Plot are not the same as those found in the MODFLOW properties dialog due to the time matching and interpolation issues described above. The MODFLOW properties dialog shows the errors computed by MODFLOW for the observations at the actual observation times and is therefore superior. The errors reported by MODFLOW have nothing to do with the model output times, only observation times.
Plot creation
Error Summary plots are created in the Plot Wizard by setting the plot type to Error Summary. A sample plot is shown in the figure.
Error Summary Plot Options
After the plot type is set in the first step of the Plot Wizard, the Next button is clicked to move to the second step of the Plot Wizard.
- Coverage: Displays the name of the coverage where the current data for the plot is coming from.
- Measurement: This is the name of the current measurement, created in the Feature Objects | Attributes dialog, being plotted.
- Feature Objects: Displays which feature object is utilized in the current plot, points or arcs.
| 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 |  |
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