Working with Geoprocessing Tools in Scripts

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Working with Geoprocessing Tools in Scripts

• Geo 599
• Week 5, Oct. 26, 2009

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Topics for today

• Strings as object names
• Workspaces
• Calling geoprocessing tools in scripts
• Listing data

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Strings as Object Names

• Most complex ArcGIS objects are referred to by
  their names
• Names are represented as strings
• Full object is attached to name behind the scenes
• Name strings can be manipulated just like any
  other string

• Most generally, names include the full path

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Path name strings

• Full path name includes drive and all folder
  levels
• Feature data sets are treated like folders

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Escaping Characters

• Not all characters can be simply included in
  strings
• Special characters and whitespace are escaped
• Python uses a backslash (\) to escape
• Backslash is stripped and potentially problematic
  character following it remains (or is converted)

• Common escape sequences
• Backslash \\
• Double quote \
• New line \n
• Tab \t

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Building Path Name Strings, os.sep

• Often want to access several items in the same
  root path
• Store root path in a variable
• Concatenate with each item
• os (operating system) module contains sep data
  item

• os.sep contains the character the operating
  system uses to separate pathname components

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Example of Building Path Name Strings

• import os
• GeoDB C\\Geo599_Python\\Geo599_Python_ExData.g
  db
• MidwestDS GeoDB os.sep MetRegions_SC1_MW
• SouthDS GeoDB os.sep MetRegions_SC1_S

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The Workspace

• Geoprocessor object has workspace attribute
• Workspace serves as default root path
• Objects without full path specified are assumed
  have the workspace as their root
• Operations on a folder act on the workspace
• Workspace may be changed during a script

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Example of using workspace

• import arcgisscripting
• gp arcgisscripting.create(9.3)
• gp.workspace C\\Geo599_Python\\Geo599_Python_E
  xData.gdb
• MidwestDS MetRegions_SC1_MW
• SouthDS MetRegions_SC1_S

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Pair and Compare

• Object and Path name strings
• Workspaces

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Geoprocessing Tools

• Geoprocessing tools are methods of the
  geoprocessor object
• Method exists for each tool in ArcToolbox
• For each tool ArcGIS help includes

• Tools script syntax
• Description and data type of each parameter
• Script example

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Toolboxes

• Toolbox organization is the same as seen in
  ArcToolbox
• Toolboxes containing tools used in a script must
  be added
• gp.AddToolbox(ltfull path location of toolboxgt)
• When using tools, toolbox must be specified

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Specifying Toolboxes

• As part of the tools name, after an underscore
• gp.ltToolgt_ltToolboxgt(ltparametersgt)
• Toolbox name is included in tool syntax in help
• By setting the Toolbox attribute of the
  geoprocessor
• gp.Toolbox ltToolboxName as stringgt
• Tools in the current toolbox can be accessed with
  just the tools name

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Geographic objects as parameters

• Most tools take geographic objects as input
  and/or output
• Parameter used is the string naming the object
• If string does not include full path, object
  assumed to be in current workspace
• Can always specify full path

• String/object often stored in a variable to
  simplify call to tool

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Optional Parameters and Defaults

• Some parameters of tools are optional
• Optional parameters have default values
• A pair of double quotes () means use the
  default
• Default values are indicated in parameter
  descriptions
• Parameter order matters!

• Any optional parameters you want to specify must
  follow the correct number of default place holders

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Explore some tools

• Look at the help files for a few geoprocessing
  tools
• Scripting information is at the end of the help
  file
• Pay attention to
• Toolbox name
• Parameter data types
• Required/optional parameters
• Default values

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Listing Data

• Geoprocessor contains several List methods
• ListDatasets
• ListFeatureClasses
• ListFields
• ListTables
• Each returns a Python list
• Batch processing done by iterating over list

• ListWorkspaces
• ListIndexes
• ListRasters

• Most List methods act on the current workspace

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Wildcards

• List methods allow specification of wildcards
• Wildcards serve as a filter
• Only the objects with names matching a specified
  pattern will be included in the list
• Wildcards specified as a string including an
  asterisk
• Asterisk () stands for any string

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Example Listing Feature Classes

• gp.workspace GeoDB os.sep
  MetRegions_SC1_MW
• Center_FCs gp.ListFeatureClasses(Ctr)
• for fc in Center_FCs
• ltprocessing stepsgt

• How many elements will the list have?
• What will they be?

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Exercise 3 Batch Processing

• Part A (10 pts.) Export the model you created in
  exercise 1 as a script and examine it
• Part B (30 pts.) Add comments to
  MetroRegMultiClip.py
• Some already included for things we havent
  covered yet
• Script sections separated by blank lines
• Each section should have a comment
• Dont forget a header

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Exercise 3 (cont.)

• Part C (50 pts.) Write a batch processing script
• Create new regional boundaries by buffering the
  Urbanized Area for each metro region in the
  course geodatabase
• Pseudocode provided
• Can borrow from MetroRegMultiClip.py, especially
  for things we havent covered yet
• Remember to comment your script

• Exercise 3 due next week (Nov. 2)