Fractal Dimension Analysis

• For a description of what the fractal dimension is and how RivEX calculates it, click here.  The rest of this page is about the operational use of RivEX for extracting the required values to calculate the fractal dimension.

• RivEX will accept and process data stored as latitude/longitude, but to obtain any meaningful data from the fractal analysis you must re-project your data into a projection that uses meters. For latitude/longitude data, one unit of measurement in the X axis is not equivalent to one unit of measurement in the Y axis, and this changes with latitude.  This makes it impossible to create a grid for fractal dimension analysis.

• A single catchment or all catchments in the whole river network can be processed, thus a large network with many catchments will generate a large number of tables\worksheets.

• To compute the fractal dimension you must complete the parameters section of the main interface and press the Build button.

• Select the Analyse Network tab and tick the Fractal dimension check box.  The following warning message is always displayed to remind you that choosing a small cell size for a large catchment may require long processing times.

• Click on Go! and the fractal dimension settings dialog is displayed. You can add cell sizes manually or auto build them over a specified range. Double clicking on a value in the list will calculate the number of cells that the grid will be composed of. Very large number of cells may crash the computer! Finally you have the option to process a single catchment or process all individually.

• Once you have defined the cell sizes and which catchment(s) to process, click OK to continue.  RivEX assumes you may have changed the default field names so you will be asked to identify the field that is the catchment ID field. You also have the option to keep the grids after processing.  The default is too destroy the grid Shapefiles after processing.

• Once you press OK, RivEX will begin to process your river network.  The status bar in the application window will display it's progress.  Once the processing has finished, you will be asked where to direct the output as shown below.

• Select YES sends the output to MS Excel.  The Excel application will minimise when data transfer has completed, do not click on the window until this has happened!

• Select NO sends the output to dbase files stored in C:\RivEX\Output.  If these files exists already you will be asked to overwrite them.  The dbase files use the naming convention of CatchID_xxx_FD_Output.dbf where xxx is the catchment ID number.

• If you send the data to a dbase file then only the box counting values are saved.  If the data is sent to Excel, the same information is saved as well as calculating the fractal dimension.  The below screen shot from Excel shows a typical output. Note each catchment is stored in a separate worksheet, in this example catchment 78 is being displayed.

You may have chosen to keep the grids generated by RivEX.  These could be useful for display or future analyses.  The Shapefiles stored in C:\RivEX\Output use the file naming convention of Layername_CatchID_ID_cellsize_xxx .shp where Layername is the name of the river network, ID  is the catchment ID number and xxx is the cell size.  Each cell of the grid records the following information.

• Unique ID
• Cell size
• Area of cell
• Minimum X coordinate
• Minimum Y coordinate
• Maximum X coordinate
• Maximum Y coordinate
• Centroid X coordinate
• Centroid Y coordinate

• The screen shot below shows a grid layer loaded into ArcMap with its attribute table open and a single cell highlighted.