Sampling Options
The Total Number Nodes is the total number of nodes contained in the model from which sampling points will be made.Sampling Locations
The user can control the total number of random locations to sample and change the 'Seed'. Each Seed value corresponds a different random spatial configuration sampling locations.If there are multiple vertical layers in the model, the layer to be used for sampling is controlled by the 'Random Layer', 'Current Computational Layer', or the 'Current Geolayer' sub options. The vertical elevation is taken from the middle of the computational layer or geolayer (depending which option is selected). The same is true for 'Random Layer'; the vertical elevation is taken from the middle of a randomly selected computational layer in the model.
By default, the box next to 'XY based' is not checked. This means sampling is done on an "IJ basis" - values are sampling exactly at model node locations defined by a set of random (I,J) integer coordinates. Checking 'XY based' creates a set of random (X,Y) real number coordinates and then maps them to model (I,J) coordinates.
Sampling Parameter
The following model parameters are available for sampling: hydraulic conductivity, head, concentration, and top elevation. Only one parameter may be selected at a time.Nugget Effect
The nugget effect can be used to add 'noise' (sampling error) to the sampling locations (check the box next to 'Nugget Effect').The collective variability added to the sampling points is controlled by the 'Std' option - or number of standard deviations to reflect in the sampling data.
The default 'Mean' value of zero means the positive and negative errors are balanced in the overall data set. Change to a positive or negative value to reflect systematic bias in the dataset.
Check the box next to 'in Log Scale' when applying the nugget effect from a parameter with significant variability (e.g., multiple orders of magnitude) such as hydraulic conductivity or concentration.
Format for Automatic Calibration
Check this box to output sampled head data in a format needed for automatic calibration (setup under Solver Options, Simulation Settings tab of the Domain Attributes menu).Create Sampling Points
Click this button to apply the set of selected options and create a set of sampling points. The results are shown in the text box once extraction is completed. The first (header) line includes following text:WellID,Time,X, Y,Zf,Zt,LyrIndex,V,Icolor
One observation per line may be added after the first line.
• the 1st value is the sampling point ID (WellID)
• the 2nd is the current time step in the case of transient modeling, expressed as the number of days from the simulation starting date. For steady simulations, a ‘0’ value is used to indicate that the comparison is for steady state.
• the 3rd is the x-coordinate of the observation (X), e.g., longitude
• the 4th is the y-coordinate of the observation (Y) , e.g., latitude
• the 5th is the sampling elevation (Zf), in units of meters above sea level.
• the 6th is again the sampling elevation (Zt), in units of meters above sea level.
• the 7th is the layer index (LyrIndex), which is set to ‘0’ so that the Zf and Zt values are used
• the 8th is the sampled value, either hydraulic conductivity (units of m/d); head (units: m); concentration (mg/L); or top elevation (m).
• the 9th is used to specify long-type RGB (Red-Green-Blue) color of the data markers in the calibration plot.
Click 'Save to File' to download .txt file of the sampling points information. Alternatively, use keyboard shortcuts to select and copy the data for use in another software.
Additionally, markers indicating sampling locations are shown in the map display. Click on a marker to shown the sampling information for that sampling point. Or click the 'Hide Sampling Points on Maps' button in the interface to temporarily hide the markers. (Note the button toggle to re-display the points.)