Calculate the volumes and masses of soil, and chemicals in soils and ground water.
Calculate the volumes and masses of soil, and chemicals in soils and ground water at each cell.
Calculate the surface area of the entire field input.
Calculate and display statistics about the data contained in the selected file.
Analyze the statistical distribution of a single data from a field.
Perform initial site assessment and well location planning.
Subsections of Analysis
volumetrics
The volumetrics module is used to calculate the volumes and masses of soil, and chemicals in soils and ground water, within a user specified constant shell (surface of constant concentration), and set of geologic layers. The user inputs the units for the nodal properties, model coordinates, and the type of processing that has been applied to the nodal data values, specifies the subsetting level and soil and chemical properties to be used in the calculation, and the module performs an integration of both the soil volumes and chemical masses that are within the specified constant shell. The results of the integration are displayed in the EVS Information Window, and in the module output window.
The volumetrics module computes the volume and mass of everything passed to it. To compute the volume/mass of a plume, you must first use a module like plume or intersection to subset your model.
NOTE: Do not use plume shell or intersection shell upstream of volumetrics since their output is a hollow shell without any volume.
The volumetrics module computes volumes and masses of analytes using the following method:
- Each cell within the selected geologic units is analyzed
- The mass of analyte within the cell is integrated based on concentrations at all nodes (and computed cell division points)
- The volumes and masses of all cells are summed
- Centers of mass and eigenvectors are computed
- For soil calculations the mass of analyte is directly computed from the computed mass of soil (e.g. mg/kg). This is affected by the soil density parameter (all densities should be entered in gm/cc).
- For groundwater calculations, the mass of analyte (Chemical Mass) is computed by first determining the volume of water in each cell. This uses the porosity parameter and each individual cell’s volume. From the cell’s water volume, the mass of analyte is directly computed (e.g. mg/liter).
- The volume of analyte (Chemical Volume) is computed from the Chemical Mass using the Chemical Density parameter (all densities should be entered in gm/cc).
Connecting the second moment output port of volumetrics to the viewer will display the Second Moment Ellipsoid and the Eigenvectors (if turned on). Spatial Moment Analysis involves computing the zeroth, first, and second moments of a plume to provide measures of the mass, location of the center of mass, and spread of the plume.
Ports
| Direction | Name | Type | Description |
|---|---|---|---|
| Input | Input Field | Field | The field to use for subsetting and calculations. |
| Input | Z Scale | Number | The factor used to remove vertical scaling. |
| Input | Explode | Number | The value used for collapsing input based on exploded geology. |
| Input | String For Output | String | String to be added at the beginning of the Output Results file. |
| Input | Trigger | Other | Port that when changed causes the module to run. |
| Output | Average Concentration. | Number | The average concentration value. |
| Output | Soil Volume Level | Number | The resulting soil volume value. |
| Output | Soil Mass Level | Number | The resulting soil mass value. |
| Output | Chemical Volume Level | Number | The resulting chemical volume value. |
| Output | Chemical Mass Level | Number | The resulting chemical mass value. |
| Output | Volume Dollars | Number | The volume in volume dollars. |
| Output | Mass Dollars | Number | Mass in mass dollars. |
| Output | Nodal Data Component | String | Text containing the name of the current analyte. |
| Output | Volume Units | String | Text containing the name of the current volume units. |
| Output | Mass Units | String | Text containing the name of the current mass units. |
| Output | Output Second Moment Object | Renderable | A renderable object displaying the second moment ellipse and mass lines. |
Properties
| Property | Type | Description |
|---|---|---|
| Allow Run | Boolean | When the Allow Run toggle is set to on the module will run every time a setting is changed. |
| Execute | Button | This button will force the module to run even if the Allow Run toggle has been turned off. This allows the user to make a number of changes before updating. |
| Z Scale | Double | The Z exaggeration factor applied to the input field. |
| Explode | Double | The Explode factor applied to the input field. |
| Update Information Window | Boolean | Send report to the Information window every time the module is run. |
Input Settings
| Property | Type | Description |
|---|---|---|
| Nodal Data Component | Choice | The Nodal Data Component used to subset the input. Options are populated from the input field. |
| Cell Sets | Multi-select | The Cell Sets selection list allows the user to select which of the cell sets (or possibly geologic layers) the volumes and masses will be calculated in. |
| Nodal Units | Linked Analyte Unit | The Nodal Units are set based on the input data and the selected Nodal Data Component. The Multiplier is the ratio of the users input units to grams/grams. The Calculation Type determines what type of units to process the Nodal Data Component in. |
| Coordinate Units | Linked Coordinate Unit | The Coordinate Units are set based on the coordinate units of the input model. The Multiplier is the ratio of the users input units to Liters. |
Processing Settings
| Property | Type | Description |
|---|---|---|
| Porosity | Double | The Porosity value allows the user to input the properties of the soil matrix in which the chemicals reside. |
| Soil Density | Double | The Soil Density value allows the user to input the properties of the soil matrix in which the chemicals reside. |
| Chemical Density | Double | The Chemical Density value allows the user to input the density of the chemical constituent for which mass estimates are being completed. This value is used to calculate the volume of chemical in the specified isosurface, as the mass units are calculated directly from the nodal data. |
| Water Density | Double | The Water Density value allows the user to specify the density of water. The default of 0.9999720 g/mL is the Density of Water at 4.5 degrees Celsius. |
| Volume Dollars | Double | The Volume Dollars value is used along with the total volume of the chemical to indicate the cost of the removal of the chemical. |
| Mass Dollars | Double | The Mass Dollars value is used, along with the total chemical mass, to determine the value of the chemical mass. |
Output Settings
| Property | Type | Description |
|---|---|---|
| Volume Units | Choice: Cubic Feet, Cubic Yards, Cubic Meters, Liters, Acre Feet, Barrels, Specify | Volume Units is used to select which units the volume should be calculated in. |
| Volume Units Ratio | Double | If the Volume Units is set to Specify the user must set the Volume Units Ratio. The ratio should be the factor needed to convert between the user specified units and liters. |
| Volume Specified Units | String | If the Volume Units is set to Specify the user must set the Volume Specified Units. This label will be used in the output. |
| Mass Units | Choice: Kilograms, Metric Tons, Pounds, U.S. Short Tons, Ounces (Troy), Specify | Mass Units is used to select which units the mass should be calculated in. |
| Mass Unit Ratio | Double | If the Mass Units is set to Specify the user must set the Mass Unit Ratio. The ratio should be the factor needed to convert between the user specified units and kilograms. |
| Mass Specified Units | String | If the Mass Units is set to Specify the user must set the Mass Specified Units. This label will be used in the output. |
| Output Results To File | Boolean | The Output Results To File toggle causes volumetrics to write a file, specified by the Filename, that contains all volumetrics information in a format suitable for input to programs like Excel (tab delimited .txt file). This file is written to in an append mode. |
| Output String | String | The Output String will output a leading string for every entry into the output file. |
| Filename | File | If the Output Results To File toggle has been selected the output filename must be set. |
| Output Filetype | Choice: Tabbed File (Excel), Mirror Display, Tabbed Multi-Line | The Output File Type choice is used to select the format of the output file. The default is a tab spaced single line output, the second choice will format the output the same as the display window, and the third option will format the output separated by tabs on multiple lines. |
| Overwrite File | Boolean | The Overwrite File toggle causes the output file to be written over instead of appended to. |
Area Moment Of Inertia
| Property | Type | Description |
|---|---|---|
| Display Mass Along Major Eigen Vector | Boolean | The Display Mass Along Major Eigen Vector allows the user to toggle the visibility along the Major Eigen Vector. |
| Display Mass Along Minor Eigen Vector | Boolean | The Display Mass Along Minor Eigen Vector allows the user to toggle the visibility along the Minor Eigen Vector. |
| Display Mass Along Interm Eigen Vector | Boolean | The Display Mass Along Interm Eigen Vector allows the user to toggle the visibility along the Intermediate Eigen Vector. |
| Segments In Lines | Integer | The Segments In Lines allows the user to control the number of segments making up each line, the larger the number of segments the closer the node data along the line will match the node data of the model, but at the cost of speed. |
| Color Lines By Axis | Boolean | The Color Lines by Axis toggle strips the node data from the lines leaving them colored by the axis they represent. |
| Ellipsoid Resolution | Integer | Ellipsoid Resolution is an integer value that determines the number of faces used to approximate the analytically smooth ellipsoid. The higher the resolution the smoother the ellipsoid. |
| Ellipsoid Scale | Double | The Ellipsoid Scale is a scaling factor for the second moment ellipsoid. A value of 1.0 (default) is analogous to one-sigma (67%) statistical confidence. Higher values would provide an indication of the size of the eigenvalues with a higher statistical confidence. |
| Ellipsoid Color | Color | The second moment ellipse is a solid color which can be selected using this control. |
Volumetric Output
| Property | Type | Description |
|---|---|---|
| Total Soil Volume | Double | The total soil volume output. |
| Total Soil Mass | Double | The total soil mass output. |
| Chemical Volume | Double | The output chemical volume. |
| Chemical Mass | Double | The output chemical mass. |
| Average | Double | The Average Concentration of the selected analyte. |
| Volume Dollars | Double | The volume in volume dollars. |
| Mass Dollars | Double | The mass in mass dollars. |
| Center Of Mass | Coordinate 3D | The Center Of Mass of the output volume. |
cell volumetrics
The cell volumetrics module provides cell by cell volumetrics data. It creates an output field with volume, contaminant mass, and cell centers for every cell in the grid. The user selects the analyte, cell sets, units, and soil properties, and the module computes volumetric data on a per-cell basis. Results can optionally be written to a tab-delimited file suitable for import into programs like Excel.
Ports
| Direction | Name | Type | Description |
|---|---|---|---|
| Input | Input Field | Field | The field to use for calculations. |
| Input | Z Scale | Number | The factor used to remove vertical scaling. |
| Input | Explode | Number | The value used for collapsing input based on exploded geology. |
| Input | String For Output | String | String to be added at the beginning of the Output Results file. |
| Output | Output Field | Field | The main output field with cell volumetric data. |
Properties
| Property | Type | Description |
|---|---|---|
| Allow Run | Boolean | When the Allow Run toggle is set to on the module will run every time a setting is changed. |
| Execute | Button | This button will force the module to run even if the Allow Run toggle has been turned off. This allows the user to make a number of changes before updating. |
| Z Scale | Double | The Z exaggeration factor applied to the input field. |
| Explode | Double | The Explode factor applied to the input field. |
Input Settings
| Property | Type | Description |
|---|---|---|
| Nodal Data Component | Choice | The Nodal Data Component used to subset the input. Options are populated from the input field. |
| Cell Sets | Multi-select | The Cell Sets selection list allows the user to select which of the cell sets (or possibly geologic layers) the volumes and masses will be calculated in. |
| Nodal Units | Linked Analyte Unit | The Nodal Units are set based on the input data and the selected Nodal Data Component. The Multiplier is the ratio of the users input units to grams/grams. The Calculation Type determines what type of units to process the Nodal Data Component in. |
| Coordinate Units | Linked Coordinate Unit | The Coordinate Units are set based on the coordinate units of the input model. The Multiplier is the ratio of the users input units to Liters. |
Output Settings
| Property | Type | Description |
|---|---|---|
| Volume Units | Choice: Cubic Feet, Cubic Yards, Cubic Meters, Liters, Acre Feet, Barrels, Specify | Volume Units is used to select which units the volume should be calculated in. |
| Volume Units Ratio | Double | If the Volume Units is set to Specify the user must set the Volume Units Ratio. The ratio should be the factor needed to convert between the user specified units and liters. |
| Volume Specified Units | String | If the Volume Units is set to Specify the user must set the Volume Specified Units. This label will be used in the output. |
| Mass Units | Choice: Kilograms, Metric Tons, Pounds, U.S. Short Tons, Ounces (Troy), Specify | Mass Units is used to select which units the mass should be calculated in. |
| Mass Unit Ratio | Double | If the Mass Units is set to Specify the user must set the Mass Unit Ratio. The ratio should be the factor needed to convert between the user specified units and kilograms. |
| Mass Specified Units | String | If the Mass Units is set to Specify the user must set the Mass Specified Units. This label will be used in the output. |
| Output Field Data | Multi-select: Current Cell, Cell Center X, Cell Center Y, Cell Center Z, Soil Volume, Soil Mass, Chem Volume, Chem Mass, Average Concentration | The Output Field Data allows the user to select which cell data components to include in the Output Field. |
| Output Results To File | Boolean | The Output Results To File toggle causes volumetrics to write a file, specified by the Filename, that contains all volumetrics information in a format suitable for input to programs like Excel (tab delimited .txt file). This file is written to in an append mode. |
| Overwrite File | Boolean | The Overwrite File toggle will create a new file when on or append to a file when off. |
| Filename | File | The filename for output. |
compute surface area
The compute surface area module is used to calculate the area of the entire field input. The input data must be a two dimensional data field output from a 2D estimation, slice, or any subsetting module which outputs two-dimensional data (slice, plume with 2D input, or plume shell). The module can compute either the full 3D surface area or the projected 2D plan area. The results of the integration are updated each time the input changes.
Ports
| Direction | Name | Type | Description |
|---|---|---|---|
| Input | Input Field | Field | The field to use for subsetting. |
| Input | Input Z Scale | Number | The factor for vertical scaling. |
| Output | Output Area | Number | The integrated area. |
| Output | Units | String | The integrated area units. |
Properties
| Property | Type | Description |
|---|---|---|
| Z Scale | Double | The Z Scale is required to assure that computed area is conformal to scaled input data. |
| Area To Compute | Choice: 3D Surface Area, 2D Plan Area | Controls whether the 3D surface area of the input field or the projected 2D area is computed. |
| Integrated Area | Double | The Integrated area of the input field. Read-only output value. |
| Area Units | String | The units of the input field squared. Read-only output value. |
file statistics
The file statistics module is used to check the format of .apdv, .aidv, .geo, .gmf, .vdf, and .pgf files, and to calculate and display statistics about the data contained in these files. This module also calculates a frequency distribution of properties in the file. During execution, file statistics reads the file, displays an error message if the file contains errors in format or numeric values, and then displays the statistical results in the EVS Information window.
Ports
| Direction | Name | Type | Description |
|---|---|---|---|
| Input | Input Filename | String | File used to display data. |
| Input | Input Z Scale | Number | The factor for vertical scaling. |
| Output | Output Filename | String | File used to display data. |
| Output | Output Z Scale | Number | The factor for vertical scaling. |
| Output | Sample Data | Field | A field containing the sample point data. |
| Output | Sample Object | Renderable | A renderable object displaying the sample data. |
| Output | Mean Level | Number | The calculated mean value. |
| Output | Median Level | Number | The calculated median value. |
| Output | Minimum Level | Number | The calculated minimum value. |
| Output | Maximum Level | Number | The calculated maximum value. |
| Output | Number Of Points | Number | The input number of points. |
| Output | Statistics | String | String representing the calculated statistics. |
Properties
| Property | Type | Description |
|---|---|---|
| Allow Run | Boolean | This toggle can prevent the module from running. Allowing the user to make changes to large data sets without waiting for updates. |
| Execute | Button | This button will force the module to run even if the Allow Run toggle has been turned off. This allows the user to make a number of changes before updating. |
| Filename | File | The file name to process for display. |
| Use Application Origin | Boolean | When true, the module will apply the Application Origin. When false, data will be left in internal model space. Turn off when loading data intended to use as a glyph or similar. |
Data Processing
| Property | Type | Description |
|---|---|---|
| Component Or Layer | Integer | The Data Component is used to select which file data component to process for display. |
| Data Processing | Choice: Linear Processing, Log Processing | Data Processing will allow the module to be run in either Linear or Log Space. |
| Z Scale | Double | The Z Scale is the vertical exaggeration to be applied to the output object. |
| Log Post Processing Clip Min | Double | Post Processing Clip Min will be used after data processing to replace any sample property value that is less than the specified number in log space. |
| Linear Post Processing Clip Min | Double | Linear Post Processing Clip Min will be used after data processing to replace any sample property value that is less than the specified number in linear space. |
| Detection Limit | Double | The Detection Limit value affects any file values set with the ‘ND’ or other non-detect flags. When the module encounters this flag in the file it will insert a value equal to (Detection Limit * LT Multiplier). |
| Less Than Multiplier | Double | The Less Than Multiplier is the value applied to any sample with the ‘<’ less than flag. |
| Number Of Bins | Integer | The Number of Bins value allows the user to specify the bins that will be used to calculate the frequency histogram. The default value of 0 does not calculate a frequency distribution during execution of the module. The user can select any number of bins from 2 to 255 (note that a value of 1 is not valid). |
| Delimiter | String | The Delimiter specifies how the labels and values in the Output Log are separated. The word TAB will be replaced by a tab advancement. |
| Coordinate Precision | Integer | The Coordinate Precision is the number of decimal points to use for coordinate values. |
| Format Data | Number Formatting | The Format Data control allows the user to set how data will be formatted for display. |
| Detailed Statistics | Boolean | The Detail Statistics toggle causes the module to display the original statistical information along with more detailed statistics. |
Glyph Settings
| Property | Type | Description |
|---|---|---|
| Points As Glyphs | Boolean | The Points As Glyphs toggle will cause the points to be displayed as a user selected glyph. |
| Point Width | Integer | The Point Width sets the size of the rendered pixels. The default is 0 which is equivalent to 1. |
| Glyph Size | Double | The Glyph Size value is used to scale the glyphs in all directions. The default is automatically computed based on your input data. |
| Priority | Choice: Maximum, Minimum | The Priority of the glyph will reverse the scaling so that the smallest sample values have the largest size. |
| Minimum Scale Factor | Double | The Minimum Scale Factor scales the sample values with the least Priority. |
| Maximum Scale Factor | Double | The Maximum Scale Factor scales the sample values with the greatest Priority. |
| Use Log Data | Boolean | The Use Log Data toggle will force the size of the glyph to be based on the log10 of the selected data. |
| Generated Glyph | Choice: Sphere, Cube, Cone, Cylinder, Polygon, Disk | The Generated Glyph choice allows the user to select the type of glyph that is automatically generated. |
| Sphere Subdivisions | Integer | The Sphere Subdivisions defines how finely the sample spheres are rendered. Higher values mean smoother spheres but at a higher memory cost. |
| Glyph Resolution | Integer | The resolution for generated cone, polygon, cylinder, and disk glyphs. |
| Primary Axis Factor | Double | The scale factor for the primary axis of the glyph. |
| Secondary Axis Factor | Double | The scale factor for the secondary axis of the glyph. |
| Heading Dip | Heading/Dip | The Heading and Dip values are used to align the glyphs to a constant orientation. |
| Roll | Double | The roll of the glyph along its primary axis. |
Time Settings
| Property | Type | Description |
|---|---|---|
| Chem File Is Time Domain | Boolean | The Chem File is Time Domain toggle turns on date interpolation for time domain analyte (e.g. chemistry) files. |
| Specify Date By Component | Boolean | The Specify Date by Component toggle will cause the Date field to be ignored and the date to be selected using the Data Component. |
| Date For Interpolation | Date | The Date For Interpolation field is the date being interpolated to. The Date can be either set here or passed in via the Date port. |
| Analyte Name | String | The Analyte Name field is used for AIDV and APDV time files as the dates take up the spots in these files usually reserved for analyte names. |
| Interpolation Type | Choice: Direct Interpolation Only, Interpolate Only, Interpolate and Extrapolate Beyond, Interpolate and Extrapolate, Interpolate (Use with Shrink) | There are 5 different Interpolation Methods that are available, each interpolation method is used to define how to interpolate when given non-detects in a file. |
| Use Nearest Measured Data | Boolean | The Use Nearest Measured Data toggle causes the sample at the interpolated date, to have the same value as the nearest measured date and not an interpolated value. |
| Non Linear Shrink | Boolean | If the Non-Linear Shrink toggle is selected the size of the sphere will be determined by a cosine interpolation instead of a linear one. |
statistics
The statistics module is used to analyze the statistical distribution of a field with nodal data. The data field can contain any number of data components. Statistical analyses can only be performed on scalar nodal data components. An error occurs if a statistical analysis is attempted on vector data. Output from the statistics module appears in the EVS Information Window. Output consists of calculated min and max values, the mean and standard deviation of the data set, the distribution of the data set, and the coordinate extents of the model.
The first port (the leftmost one) should contain a mesh with nodal data. If no nodal data is present, statistics will only report the extents and centroid of your mesh. Data sent to the statistics module for analysis will reflect any data transformation or manipulation performed in the upstream modules. Any mesh data sent to the port is used for calculating the X, Y and Z coordinate ranges. The mesh coordinates have no effect on the data distribution. Cell based data is not used.
Ports
| Direction | Name | Type | Description |
|---|---|---|---|
| Input | Input Field | Field | The field to use for statistic calculations. |
| Input | Z Scale | Number | The factor used to remove vertical scaling. |
| Output | Mean Level | Number | The calculated mean value. |
| Output | Median Level | Number | The calculated median value. |
| Output | Minimum Level | Number | The calculated minimum value. |
| Output | Maximum Level | Number | The calculated maximum value. |
| Output | Number Of Points | Number | The input number of points. |
| Output | Statistics | String | String representing the calculated statistics. |
Properties
| Property | Type | Description |
|---|---|---|
| Allow Run | Boolean | When the Allow Run toggle is set to on the module will run every time a setting is changed. |
| Execute | Button | This button will force the module to run even if the Allow Run toggle has been turned off. This allows the user to make a number of changes before updating. |
| Z Scale | Double | The Z exaggeration factor applied to the input field. |
Statistic Settings
| Property | Type | Description |
|---|---|---|
| Data Component | Choice | The Data Component on which the statistical analysis is to be performed. Options are populated from the input field. |
| Minimum Data Level | Double | The Minimum Data Level is used to set the lower limit on the data bins for statistical analysis. The default value is the minimum in the data component. If the statistical distribution should focus on only a portion of the data, this value can be changed to reflect only that desired range of data. |
| Maximum Data Level | Double | The Maximum Data Level is used to set the upper limit on the data bins for statistical analysis. The default value is the maximum in the data component. If the statistical distribution should focus on only a portion of the data, this value can be changed to reflect only that desired range of data. |
| Clamp Data | Boolean | The Clamp Data toggle will actually clamp the data to the Minimum and Maximum Data Level before processing it for statistics. |
| Number Of Bins | Integer | The Number of Bins is used to set the number of distribution bins to be used in the analysis. The default is 10 and the range is from 2 to 255. This value is generally changed to get unary or aesthetically pleasing bin values. |
| Details | Boolean | The Details toggle will display additional statistical information such as variance, deviation and quartile values. |
| Report Delimiter | String | The Report Delimiter string controls the spacing of the output window. The text of the output window will be broken up according to whatever is in the Delimiter box. The special delimiter tag ‘TAB’ allows the text to be tab delimited. |
| Coordinate Precision | Integer | The Coordinate Precision is the number of decimal points to use for coordinate values. |
| Format Data | Number Formatting | The Format Data control allows the user to set how data will be formatted for display. |
site planning
The site planning module is used to perform initial site assessment and well location planning. It generates and distributes a specified number of points within the bounds of an input field using an iterative algorithm. The module supports fixed user-specified points and can filter output by cell set type. Results can be displayed as vertices or sphere glyphs.
Ports
| Direction | Name | Type | Description |
|---|---|---|---|
| Input | Input Bounds | Field | The input field defining the spatial bounds for site planning. |
| Input | Fixed Points | Field | Optional fixed points that remain in place during the iterative distribution. |
| Output | Output Field | Field | The output points. |
| Output | Output Renderable | Renderable | A renderable object to display. |
Properties
| Property | Type | Description |
|---|---|---|
| Allow Run | Boolean | This toggle can prevent the module from running. Allowing the user to make changes to large data sets without waiting for updates. |
| Execute | Button | If Allow Run is turned off the Execute button will force the module to run once with the current settings. |
Settings
| Property | Type | Description |
|---|---|---|
| Number Of Points | Integer | The number of points to generate and distribute within the bounds. |
| Iterations | Integer | The number of steps the iterative point distribution performs. Up to a certain point a higher value usually yields better results, at the cost of speed. |
| Fixed User Points | Coordinate Array 2D | The Fixed User Points option is used to add fixed points manually and additionally to the fixed points from the Fixed Points port. |
| Select Cell Sets | Multi-select | The Select Cell Sets control allows the user to select the site types to output. |
Display Settings
| Property | Type | Description |
|---|---|---|
| Display As Spheres | Boolean | When the Display As Spheres toggle is enabled the red port will output the sites as sphere glyphs. Otherwise the output will be vertices. |
| Glyph Size | Double | The Glyph Size value is used to scale the glyphs in all directions. The default is automatically computed based on your input data. |
| Z Scale | Double | The Z Scale is required to assure that generated sites are matched to scaled input. |
| Z Position | Double | Z Position determines the Z location of the output. This allows you to position the output at the most convenient elevation. |