The LineSlope Analyst Extension is an ArcView 3.2 Extension. The extension calculates percent slope for each line in a line theme, based on a grid Z value theme.
The LineSlope Analyst has several minimum requirements:
- ArcView Spatial Analyst (default extension)
- ArcView 3D Analyst (download the 3d version separately)
- A loaded Grid or TIN theme
- An line theme (either an ArcInfo format coverage or an ArcView format shapefile) whose table is editable
Loading the LineSlope Analyst
Running the LineSlope Analyst Extension
- Load a line theme whose table is editable.
- Load a grid or TIN theme. This theme will serve as the Z value source for calulating slope. When you have these themes loaded, the LineSlope button will be available.
- Click the LineSlope button .
- Select the line theme for which you want to calculate slope values.
If the line theme table cannot be edited, you will see the error message box:
- Select the surface theme. Both grid themes and TIN themes will be displayed.
- After you click OK, the process will progress. ArcView's application window title bar will show the progress:
- The title bar will indicate when the process is complete:
- The theme table will have a new field added (Line_slope) and the value per record calculated as described below. If either line endpoint falls outside the surface, the line slope will be calculated as -99.99.
Here is a view with road lines displayed in a graduated color classification based on calculated slope (higher slopes are deeper red):
The LineSlope Analyst Algorithm
The LineSlope Analyst algorithm is simple. For each line:
- Line length is calculated with the aShape.ReturnLength request.
- The start and end point is obtained with the aPolyLine.Along (aPercentage) for the percentages 0 and 100, respectively.
- Each point's Z value is obtained using either the aSurface.Elevation (aPoint) or the aGrid.CellValue (aPoint, aPrj) request, depending on whether the Z theme is a TIN or a grid.
- The absolute value of the difference between the minimum and maximum Z values.
- Slope is calculated as (Zdifference / length * 100%), which in generic mathematical terms is ((rise / run) * 100%).
- If either end point has no calculated Z value (i.e., the point is outside of the Z theme data extent), the slope is given the "no data" value of -99.99.
Copyright © Phil Hurvitz, 1998-2007