The Gradient Vectors layer is offered in many RockWorks map windows which create or display grid model data. It is used to display small arrows between grid nodes to represent uphill or downhill gradients. Arrows may be scaled and/or color-coded according to steepness of slope.
Gradient Vectors
Insert a check here to include the Gradient Vector layer in your map.
Click on this tab to set up the vector options.
- Direction: Choose the direction the gradient arrows are to represent, either Down-Gradient or Up-Gradient.
- Length:
- Choose Fixed if you want the map arrows to be the same length, roughly the same size as the node-to-node spacing.
- Or, choose Proportional if you want each map arrow's length to be scaled based on its slope, with flat areas plotting with short arrows and steep arrows with long arrows.
- Multiplier: Use this setting to multiply the directional vector lengths such that they extend into adjacent grid cells. This can produce a more understandable map.
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- Colors:
- Choose Fixed to set the arrows to a single color, and click the color box to select the color.
- Or, choose Proportional to set the arrows to a variable scheme, using cold colors for arrows between nodes with shallow slopes and hot colors for nodes with steep slopes, and graduating the colors in-between.
- Frequency: Use this setting to define how many gradient arrows are to be generated in the map. A setting of "1" will include vectors for all nodes in the grid model. A setting of "2" will include vectors for every other node in the model. A setting of "3", every third node, and so on.
- Filter: Enter the minimum and maximum slope values to be included in the map. Enter "0" for the minimum and "90" for the maximum if all nodes are to be included. Or, to show only those nodes with slope > 30 degrees, for example, you would enter "30" for the minimum and "90" for the maximum.
- Thickness: Click here to select the line thickness for the arrows. "1" will generate thin lines, "3" thick ones.
- Choose Fixed to set all of the arrows to a specific thickness. "1" will generate thin lines, "3" thick lines.
- Choose Proportional to set the arrows to variable thickness, using thin lines to represent shallow slopes between nodes and thick lines for steep slopes between nodes, with intermediate thicknesses in between. You can choose the minimum and maximum thicknesses using the prompts.
- Normalize Nodes: Leave this option unchecked if your grid model represents topographic elevations.
If your grid model represents something other than topography (e.g. geochemical concentrations), you should check this box so that the Z values can be normalized to map units prior to computing the slope and aspect. For example, if a grid node spacing is 10 meters and the user is analyzing geochemical data than ranges between zero and 0.01, the maximum slope would be less than one degree in which case the program would produce a blank diagram. With normalization, however, the data is now rescaled to resemble a three-dimensional cube in which the slope will have a wide range (i.e. zero to 90 degrees).
- Automatic: Using this normalization scheme, the program will rescale the grid node values such that the minimum node value will represent zero while the maximum node value will be equal to the map distance from the southwest corner to the northeast corner of the grid model. The map below illustrates a downgradient vector map based on normalized geochemical data that initially ranged between zero and 0.01.
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- Manual: Choose this option if you want to enter your own min and max range within which the grid node values are to be normalized before the analysis is run.
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