Description
Header
Flow Diagram
Help (Manual)

--------------------------------------------------------------------------------
Descpription:

A Geographic Information System (GIS) algorithm was developed to conduct piosphere analysis employing anobject-oriented programming language. Piospheres or concentration areas are surrogate indicators of a localized disturbance where the impact of disturbance, as measured by a stress response indicator, attentuates along a gradient with increasing distance from an impact area. An object-oriented programming language was successfully employed to assess the impact of grazing pressure and military troop movements at piospheres. The program provides analysis for both multiple spatial boundary scales, e.g., individual grazing paddocks, training areas, or the entire landscape, and for multiple time periods. A localized impact is represented as a vector element, i.e., point, line, or polygon, which is related to raster-based index (or impact response variable) layers. An index layer is representative of a landscape attribute such as vegetation cover or soil stability which has a predictable response to a disturbance. The program outputs an ArcView shapefile that includes tabular descriptive statistics on the response index variables.

--------------------------------------------------------------------------------
Header:
----------------------------------------------------------------------
DiskFile : piospher.ave : Piosphere
Programmer : Tom Van Niel & Robert Washington-Allen
Created : 14-Dec-98
Revisions : 05-Jan-99/Tom Van Niel/ changed Generation of Statistics procedure so it uses SAMPLE command instead of Using a looping Structure in combination with the CON command -- This can speed up the program considerably.
05-Apr-99/Tom Van Niel/ Changed Generation of Statistics again -- uses ZONAL STATS instead of SAMPLE -- Got idea from ESRI code Spatial.SummarizeZones
06-Apr-99/Tom Van Niel/ Added ability to retain individuality of piosphere theme features by allowing user to select a field in attribute table to summarize stats by.
08-Apr-99/Tom Van Niel/ Changed output fields so displayed in two separate fields instead of one combined
field.
12-Apr-99/Tom Van Niel/ Had wrong valuetheme in zonal stat table -- changed to index theme (now summarizes index theme by zones in combined grid as it should)
10-Jun-99/Tom Van Niel/ Fixed problem of program crashing when boundary theme is "larger" in extent than the index theme -- problem had to do with nodata values being counted which threw off the number of records -- fixed in "Limit size of grids" section
16-Jun-99/Tom Van Niel/ Changed output of program to be one shapefile made from combined grid -- also joined the stats table to the ftab of the shapefile.

Function : Creates Pioshpere Areas and Summarizes These areas against selected Index (GRID)
References : Andrew, M.H. 1988. Grazing impact in relation to livestock points. Trends in Ecology and Evolution 3:336-339.

Knight, A.W. 1995. REMA:A neutral model to reveal patterns and process of cover change in wooded rangelands. Remote
Sensing of Environment 52:1-14.

Pickup, G., V.H. Chewings, and D.J. Nelson. 1993. Estimating Changes in vegetation cover over time in arid rangelands
using Landsat MSS data. Remote Sensing of Environment 43: 243-263.
Called By : GUI
Calls : None
----------------------------------------------------------------------

Flow Diagram:

--------------------------------------------------------------------------------

Help (Manual):

PIOSPHERE ANALYSIS

Purpose: To calculate piospheres or impact areas from a response indicator.

General Description of Algorithm: This program depends on the user to specify a GIS layer that represents the center of the concentration area(s) or piosphere(s) and a GIS layer of the index to be summarized over the piosphere. The concentration layer and the index layer are picked from a menu of all vector or raster GIS layers, respectively, in the view of the Graphical User Interface (GUI). The concentration layer, also called a theme, is the GIS layer from which the piosphere is calculated around (e.g., watering holes). The index theme is the GIS layer that gets summarized (e.g., SAVI grid). The concentration theme can contain either point, line, or polygon features. Features can be identified from each other by a user-defined field from the theme’s feature attribute table. The user can also choose to ignore the field selection in which case a global summarization will be the default (i.e., features are summarized as one feature). The user can also choose to limit the number of annuli generated by either choosing another GIS layer to bound the calculation or by specifiying a number of iterations. The main output of this program is an ArcView shapefile which has been joined to a summary table of the index theme’s statistics. These statistics include but are not limited to minimum, maximum, mean, and standard deviation by annulus and identifier field.

Assumptions:

This program is an ArcView Avenue script, so the user must run it from within ArcView. The ArcView session must have the Spatial Analyst (SA) extension loaded. The script must run through a view in ArcView. In other words, the script must be linked to a button that is displayed in a view's Graphical User Interface (GUI) (as in the "P" button in the pic below), or run from the "script run" icon directly after the view was active. This is because the avenue "GetActiveDoc" command is used in the script which assumes that the view is the active document at the time the script is run. The View must also contain at least one feature theme (point, polygon, or line) and one ArcInfo Grid. The user will be asked to choose the concentration theme from a list of all the feature themes and the index theme from a list of all the Grids. This program will generate a shapefile and several grids to a working directory so the user will have to maintain disc space management. The shapefile is displayed in the view and the statistics are saved to the shapefiles feature attribute table (shapfilename.dbf). If a selection is present on the Piosphere Concentration Theme, only those features selected will be summarized.

Message Box: "Choose the Piosphere Concentration Theme"
A list of all feature themes (point, line, or polygon) in the view are displayed in this menu. The user should select the theme that represents the piospheres (or impact areas) to be analysed.

Message Box: "Choose the Field in Piosphere Theme to Summarize by (Cancel will not summarize by a Field)"
A list of all the number fields in the Piosphere Concentration Theme are displayed in this menu. The user should choose the field from the list that they want to maintain the attributes of. This is useful in the case where the Piosphere Concentration Theme has many features (e.g., points) that the user has an interest in analysing separately. If the user chooses the Cancel button, no field is selected and none of the features in the Piosphere Concentration Theme are summarized separately.

Message Box: "Choose the index theme(s) to summarize"
A list of all the Grid themes in the view are displayed in this menu. The user should select the grid that represents the stress response indicator. This theme is called the index theme since a common layer used here is a vegetation index.

Message Box: "Choose a Bounding Theme to Limit the Piosphere (Cancel allows you to choose a limiting number of iterations)"
A list of all feature themes in the view are displayed again. The user can select a theme that will limit the number of piosphere concentration areas (or annuli) that are generated around each concentration area in the Piosphere Concentration Theme. A commonn use of this option would be to limit the number of annuli around a watering hole (concentration theme) by the grazing compartment boundary (bounding theme). If the user selects the Cancel button, the next Message Box will appear. If not, skip over the next Message Box.

Message Box: "Choose the Number of Concentration Areas to Limit the Calculation"
The user can input a number of annuli or concentration areas to calculate around each impact area in the Piosphere Concentration Theme.

Message Box: "Enter the Number of Pixels to Define Distance of the Concentration Areas"
The user can input the number of pixels (as defined by the pixel size of the Index Theme) to define the distance of each concentration area or annuli.

Message Box: "Chart Results"
The user can choose to chart statistics (mean, min, max, standard deviation) of the index grid by concentration area.

OUTPUT
The output should look something like this:

The main output is an ArcView Shapefile (named "pio16.shp" here). The statistical summary has been "joined" to the feature table of this shapefile (seen as the table on the above pic with a selected polygon in yellow). The chart of the statistics summarized by concentration area is also displayed.

Last Updated on 30-Sep--99
By Tom Van Niel