ZONALGEOMORPH

 

summarizes for each zone of the input zone grid geomorphic calculations of the input elevation grid and records them in the output INFO table.  The geomorphic calculations include various measurements of elevation, slope, aspect, and curvature.

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ZONALGEOMORPH <zone_grid> <elevation_grid> <output_info_file> {z_factor} {geomorphic_name}

 

ARGUMENTS

 

<zone_grid> - the input integer grid that identifies the zones for which geomorphic calculations are summarized.

 

<elevation_grid> - the input integer or floating-point grid which defines the surface from which geomorphic calculations are made.

 

<output_info_file> - the name for the output INFO table to which the summaries will be reported.

 

This table will contain the VALUE and COUNT items from the <zone_grid> VAT.  It will also contain an item for each geomorphic calculation.  The name of each item is the {geomorphic_name}.

 

{z_factor} - the number of ground x,y UNITS in one surface ZUNIT in the <elevation_grid>.  Defaults to 1.

 

{geomorphic_name} - the keyword that defines which geomorphic calculations will be performed and summarized by zone.  The default is for ALL calculations to be made.  Valid keywords are:

 

ALL                     All of the following calculations are performed

ELEVATION_MEAN          Average elevation

ELEVATION_MIN           Minimum elevation

ELEVATION_MAX           Maximum elevation

SLOPE_MEAN              Average slope

SLOPE_MEAN_NET          Net average slope, taking into account variation in aspect

SLOPE_MIN               Minimum slope

SLOPE_MAX               Maximum slope

ASPECT_MEAN_NET         Net average aspect

ASPECT_STRENGTH         Degree to which aspect is scattered CURVATURE_MEAN          Average curvature

CURVATURE_MEAN_A        Average of absolute value of curvature CURVATURE_MIN           Minimum curvature

CURVATURE_MAX           Maximum curvature

 

SLOPE calculations are recorded in percent.

 

All The calculations are further described under GEOMORPHIC CALCULATIONS in DISCUSSION section.

 

 

NOTES

 

- ZONALGEOMORPH runs from the GRID module of ARC/INFO, ver. 7.0.3.

 

- During the execution of ZONALGEOMORPH the following settings are used: SETWINDOW <elevation_map>, SETCELL MAXOF, and VERIFY OFF.  The initial environment is restored when execution is completed.

 

- ZONALGEOMORPH can be run from the command line or from a menu.  When the global variable: .R6MODE is set to MENU, then running ZONALGEOMORPH will popup a menu, unless all the required arguments are provided.

 

 

DISCUSSION

 

GEOMORPHIC CALCULATIONS - The following information concerns how the geomorphic calculations are made.  For more detail refer to the actual AML: zonalgeomorph_at.aml.

 

THEMES - The calculations are broken up into 4 themes: ELEVATION, SLOPE, ASPECT, and CURVATURE.  For each cell, values are calculated in the following manner:

 

ELEVATION - values are calculated using multiplication: <elevation_grid> * {z_factor}.

 

SLOPE - values are calculated using the SLOPE function in GRID: SLOPE (<elevation_grid>, {z_factor}, PERCENTRISE).

 

ASPECT - values are calculated using GRID ASPECT:

ASPECT (<elevation_grid>) / DEG

 

CURVATURE - values are calculated using GRID CURVATURE: CURVATURE (<elevation_grid> * {z_factor}).

 

STATISTICS - The calculations are summarized using 3 basic statistics: MEAN, MIN, and MAX, and 3 more complicated statistics: MEAN_NET, MEAN_A, and STRENGTH.  For each zone, values are calculated in the following manner:

 

MEAN, MIN, and MAX - Any of the calculations whose keywords end in just MEAN, MIN, or MAX (e.g. ELEVATION_MEAN, SLOPE_MIN) are performed using the the ZONALSTATS function in GRID.  For the arguments to ZONALSTATS, the <zone_grid> is the <zone_grid>, the <value_grid> is the THEMES (see above), and the {stats_name} is either MEAN, MIN, or MAX accordingly.

 

MEAN_NET - SLOPE_MEAN_NET and ASPECT_MEAN_NET are calculated by:

 

Calculating the northern slope of each cell by multiplying the sine of aspect * slope.  Note that this is negative for southern aspects.

 

Calculating the eastern slope of each cell by multiplying the cosine of aspect * slope.  Note that this is negative for western aspects.

 

Averaging the northern and eastern slopes over each zone.

 

Calculating the net slope of each zone as a whole by taking the square root of the sum of the squares of the average northern and eastern slopes.

 

Calculating the net aspect of each zone as a whole by taking the inverse tangent (GRID ATAN2) of the average northern and eastern slopes and multiplying by the DEG constant to convert back to degrees.

 

STRENGTH - ASPECT STRENGTH is calculated by dividing SLOPE MEAN NET by SLOPE MEAN.  The values will be floating-point numbers ranging from 0 to 1.  0 being the weakest, i.e. where aspects in the zone are very scattered (e.g. a conical mountain where North, South, East, and West aspects cancel out each other).  And 1 being the strongest, i.e. where aspects in the zone are all the same (e.g. a side slope all facing the same direction).

 

MEAN_A - CURVATURE_MEAN_A is calculated the same as CURVATURE MEAN, except that the curvature values for each cell are made positive (the absolute value is taken) before they are averaged by zone.  The utility of such a statistic is that in conjunction with CURVATURE_MEAN they give a sense of the degree to which zones are dissected.  The greater is CURVATURE_MEAN_A in respect to the absolute value of CURVATURE_MEAN, the more dissected is the zone.