Extending ArcGIS via programming

1
Extending ArcGIS via programming

• Why Programming
• Automation of repetitive tasks
• Implementation of functionality not available
• Programming functionality
• Scripts (AML, VB, Python, Avenue)
• Interfaces for application programmers
• Model Builder
• ArcObjects
• COM Integration

2
Three Views of GIS
Geodatabase view Structured data sets that
represent geographic information in terms of a
generic GIS data model. Geovisualization view
A GIS is a set of intelligent maps and other
views that shows features and feature
relationships on the earth's surface. "Windows
into the database" to support queries, analysis,
and editing of the information. Geoprocessing
view Information transformation tools that
derives new geographic data sets from existing
data sets.
adapted from www.esri.com
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Examples

• TauDEM ArcMap toolbar using Visual Basic/C
  (implementation of functionality not available in
  ArcGIS)
• Visual Basic Programming of simple grid
  calculations

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TauDEM Software Functionality

• Pit removal (standard flooding approach)
• Flow directions and slope
• D8 (standard)
• D? (Tarboton, 1997, WRR 33(2)309)
• Flat routing (Garbrecht and Martz, 1997, JOH
  193204)
• Drainage area (D8 and D?)
• Network and watershed delineation
• Support area threshold/channel maintenance
  coefficient (Standard)
• Combined area-slope threshold (Montgomery and
  Dietrich, 1992, Science, 255826)
• Local curvature based (using Peuker and Douglas,
  1975, Comput. Graphics Image Proc. 4375)
• Threshold/drainage density selection by stream
  drop analysis (Tarboton et al., 1991, Hyd. Proc.
  5(1)81)
• Wetness index and distance to streams
• Water Quality Functions

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TauDEM in ArcGIS
Visual Basic ESRI ArcGIS 8.3, 9.0 Toolbar
Standalone command line applications
C COM DLL interface
Available from
TauDEM C library
Fortran (legacy) components
http//www.engineering.usu.edu/dtarb/
TauDEM Gridio
Shapelib
ESRI gridio API (Spatial analyst)
ESRI binary grid
ASCII text grid
Vector shape files
Binary direct access grid
Data formats
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Implementation Details
Spatial Analyst includes a C programming API
(Application Programming Interface) that allows
you to read and write ESRI grid data sets
directly.
Excerpt from gioapi.h / GetWindowCell - Get a
cell within the window for a layer,
Client must interpret the type of the output
32 Bit Ptr to be the type of
the layer being read from. PutWindowCell -
Put a cell within the window for a layer.
Client must ensure that the type of
the input 32 Bit Ptr is the
type of the layer being read from. / int
GetWindowCell(int channel, int rescol, int
resrow, CELLTYPE cell) int PutWindowCell(int
channel, int col, int row, CELLTYPE cell)
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C COM Methods used to implement functionality
using Microsoft Visual C
STDMETHODIMP CtkTauDEMAreadinf(BSTR angfile,
BSTR scafile, long x, long y, int doall, BSTR
wfile, int usew, int contcheck, long result)
USES_CONVERSION //needed to convert from BSTR
to Char or String result area(
OLE2A(angfile), OLE2A(scafile), x,y,doall,
OLE2A(wfile), usew, contcheck) return
S_OK
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Visual Basic for the GUI and ArcGIS linkage
Private TarDEM As New tkTauDEM Private
Function runareadinf(Optional toadd As Boolean
False) As Boolean Dim i As Long
runareadinf False i TarDEM.Areadinf(tdfile
s.ang, tdfiles.sca, 0, 0, 1, "", 0, 1) If
TDerror(i) Then Exit Function If toadd Then
AddMap tdfiles.sca, 8 End If
runareadinf True End Function
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Using TauDEM - Exercise
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Calculating the distance to a drain point (e.g.
watershed outlet or gage)

• Introduce VB scripting
• Introduce Recursion
• Isolate the Watershed draining to a point
• Could be done with the Flow Path function
  (maybe), but a programmed solution is instructive
  and can be generalized to other applications

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Distance from each grid cell to outlet along flow
path Write program to do this
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Distances
42.4
42.4
42.4
30
30
30
42.4
42.4
42.4
30
30
30
42.4
42.4
42.4
30
30
30
42.4
30
30
30
30
30
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Summing the distances down from each grid cell
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Summing the distances down from each grid cell
30
3042.4
303042.4
303042.430
Number of additions
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Recursive Approach
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Recursive Approach
30
3042.4
3072.4
30102.4
Number of additions N
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This requires (assumes) that the distance for
cell i,j is initialized or has been calculated to
start the process
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Programming the calculation of distance to the
outlet

102.4
72.4
30
72.4
42.4
0

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Visual Basic Implementation
'RECURSIVE DISTANCE CALCULATION FUNCTION Sub
DistCalc(i, j) Dim k As Integer, inb As Long,
jnb As Long For k 1 To 8  ' for each neighbor
    inb i di(k)     jnb j dj(k)     If
(inb gt 0 And inb lt nrow And jnb gt 0 And jnb lt
ncol) Then   ' guard ' against out of domain
        If pPixels(jnb, inb) gt 0 Then   ' guard
against no data             If (pPixels(jnb,
inb) - 4 k Or pPixels(jnb, inb) 4 k) Then
            ' Here we have a grid cell that
drains back to the grid cell we are at
                dPixels(jnb, inb) dPixels(j,
i) dd(k)                 DistCalc inb, jnb '
Call the function for the neighbor pixel
            End If         End If     End If
Next k End Sub
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Steps for distance to outlet program

• Read the outlet coordinates
• Read the DEM flow direction grid. This is a set
  of integer values 1 to 8 indicating flow
  direction
• Initialize a distance to outlet grid with a no
  data value
• Convert outlet to row and column references
• Start from the outlet point. Set the distance to
  0.
• Call the DistCalc function at the outlet.

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Distance Calculation VBA Exercise
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Visual Basic Programming in ArcMAP

• References
• ESRI, (1999), ArcObjects Developers Guide
  ArcInfo 8, ESRI Press, Redlands, California.
• Zeiler, M., (2001), Exploring ArcObjects. Vol 1.
  Applications and Cartography. Vol 2. Geographic
  Data Management, ESRI, Redlands, CA.

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Are there any questions ?