Programming for Geographical Information Analysis: Advanced Skills

1
Programming for Geographical Information
AnalysisAdvanced Skills

• Lecture 3 Arc Data Framework
• Dr Andy Evans

2

• Data
• Getting maps and layers
• Getting data points and attributes
• Sorting and searching

3
ArcMap IMXDocument methods

• Used for getting data
• getActiveView() i.e. layout view or data view
  data.
• getFocusMap() i.e. currently selected/shown
  map.
• getMaps() i.e. all maps.
• getSelectedItem() i.e. that the user has picked.
• getSelectedLayer() i.e. that the user has picked.
• Documents also implement IDocument, the main use
  of which is programmatically controlling toolbars.

4

• Data
• Getting maps and layers
• Getting data points and attributes
• Sorting and searching

5
Getting data
Document (.mxd file)
Map
AttributeTable
FID Data
1 234
2 875
Layer
Feature
234
Values
6
Getting a Map

• A Map contains all the data and features in the
  Data View or each Layout View frame.
• import com.esri.arcgis.carto.
• IMxDocument mxDocument (IMxDocument)app.getD
  ocument()
• IMap mxDoc mxDocument.getFocusMap()
• FocusMap is the one visible in data view or
  selected in layout view.

7
Getting all Maps

• You can also get an Object containing all the
  Maps.
• IMaps maps mxDoc.getMaps()

8
IMaps

• You can loop through all the IMap Interface
  objects in an IMaps Interface object using its
  .getCount and .getItem methods.
• IMap map null
• for (int i 0 i lt maps.getCount i)
• map maps.getItem(i)
• Other IMaps methods include
• add(IMap), create(), remove(IMap),
  removeAt(index), Reset Remove all.

9
Getting data

• Its rare we want to get data out of a Map. Its
  more usual to get data from a Layer (a
  Coverage, FeatureDataset, Image etc.).

Map
AttributeTable
FID Data
1 234
2 875
Layer
Feature
234
Values
10
Getting Layers I

• If you know what the type of the Layers are, you
  can get them thus
• // Assuming we've got a IMap object "map".
• ILayer layer null
• for (int i0 i lt map.getLayerCount() i)
• layer map.getLayer(i)
• // Do something

11
Enumerations

• Objects containing lists of other objects. Like a
  1D array.
• Arc uses them to return arrays of data to you.
• Have a next method to get the next object.
• Also a reset method to return to the start.
• ArcObject types have different Enumerations.
• e.g. IEnumLayer is the Interface for a set of
  Layers.

12
Standard use of Enumerations

• IEnumSomething enumSomething someEnumGett
  ingMethod()
• enumSomething.reset()
• SomeClass variable enumSomething.next()
• while (variable ! null)
• \\Do stuff with variable
• variable enumSomething.next()
• Note we get the first variable first, then do
  something with it, before getting the next and
  checking whether it is null.

13
Getting Layers II

• Get an Enumeration of Layers
• IEnumLayer enumLayer map.getLayers(null,true
  )
• enumLayer.reset()
• ILayer layer enumLayer.next()
• while (layer ! null)
• \\ Do something with the ILayer
• layer enumLayer.next()

14
Types of Layer

• Remember however that we can add many things as
  Layers (images, data, etc.).
• Main types
• IFeatureLayer
• IGeoFeatureLayer
• IGraphicsLayer
• Others include more specific FeatureLayers,
  FDOGraphicsLayers (Annotation), TinLayer,
  RasterLayer, and CoverageAnnotationLayer.
• If we dont know the layers in the document we
  may need to check for a specific type.

15
The instanceof keyword

• You can check whether an object implements an
  Interface using Javas instanceof keyword.
• For example, if the users selected something in
  ArcMap's tree of contents, you can test whether
  its a GeoFeatureLayer, thus
• // Assuming weve got an enumeration of Layers.
• IGeoFeatureLayer featLayer null
• ILayer layer enumLayer.next()
• while (layer ! null)
• if (layer instanceof IGeoFeatureLayer)
• featLayer (IGeoFeatureLayer) layer
• //Do something with featLayer
• layer enumLayer.next()

16

• Data
• Getting maps and layers
• Getting data points and attributes
• Sorting and searching

17
Getting Data/Features from Layers

• Assign your Layer to an appropriate Interface.
• IGeoFeatureLayer Treat as geographical data
• IFeatureLayer Treat as a general Layer
• IAttributeTable Treat as an attribute table
• Get the Attribute Table or search the Layer.

18
Getting data

• Once we have our Layer, we want to get data from
  it.

Map
AttributeTable
FID Data
1 234
2 875
Layer
Feature
234
Values
19
Getting the Attribute Table

• Assuming we have a Layer Enumeration, we set the
  Layer to an IAttributeTable.
• import com.esri.arcgis.geodatabase.
• IAttributeTable pAttributeTable
• (IAttributeTable)enumLayer.next()
• ITable table pAttributeTable.getAttributeTable()
  
• IRow row null
• for (int i 1 i lt table.rowCount(null) i)
• row table.getRow(i)
• int index table.findField("School")
• Object value row.getValue(index)

20
Getting the Attribute Table
IAttributeTable pAttributeTable
(IAttributeTable) enumLayer.next()
ITable table pAttributeTable.getAttributeTable
() IRow row null for (int i
1 i lt table.rowCount(null) i) row
table.getRow(i) int index
table.findField("School") Object value
row.getValue(index)
21
Getting data

• Alternative is to get data from a Feature.

Map
AttributeTable
FID Data
1 234
2 875
Layer
Feature
234
Values
First though, we need to get only the features we
are interested in. We can search for these.
22

• Data
• Getting maps and layers
• Getting data points and attributes
• Sorting and searching

23
Searching

• You need to get a reference to the data and a
  search cursor (ICursor / IFeatureCursor).
• The search cursor jumps between records in a
  dataset that match some search criteria.
• The cursor marks the row/feature in the dataset
  that youre currently interested in.
• They have a nextSomething method which gets a
  object appropriate to the dataset.

24
Search Methods

• IFeatureLayer / IGeoFeatureLayer
• IFeatureCursor cursor featureLayer.search
• (queryFilter, false)
• ITable from an IAttributeTable
• ICursor cursor table.search
• (queryFilter, false)
• Where queryFilter is an IQueryFilter Object
• True / false determines how the records are
  allocated to the Cursor set to False.

25
Making a QueryFilter

• You can get everything by setting these to null.
• cursor pFeatureLayer.search(null, false)
• IQueryFilter objects store fields you want
  returned and query strings.
• You need to (rare this) make a QueryFilter object
  from scratch
• IQueryFilter queryFilter
• new QueryFilter()

26
IQueryFilter Objects

• pQueryFilter.setSubFields("SCHOOL,CITY")
• pQueryFilter.addField ("POSTCODE")
• pQueryFilter.setWhereClause
• "CITY 'Leeds'"
• By default the fields are set to i.e. all
  fields, so if you use just addField youll have
  to setSubFields to first.

27
Sorting data

• You can use searching to also sort data. However,
  it is a bit hit-and-miss.
• Well look at the more usual TableSort in the
  practical.

28
Getting Data from a Feature

• Use the cursor to get the next feature
• IFeature feature featureCursor.nextFeature()
• while (feature ! null)
• //Do stuff to feature
• feature featureCursor.nextFeature()
• The Feature method getValue(i) takes in an
  integer number equalling the position of the
  field column.
• If you dont know it, there are lookup methods
  that return integers
• feature.getFields().findField("SCHOOL")

29
Setting/Getting Features Selected

• An alternative is to get the selected Features.
• To get the Features you need IMaps
  getFeatureSelection method, or an ISelectionSet
  Object.
• IMaps selectFeature method takes in an ILayer
  and IFeature.
• Refresh the display using the MxDocuments
  refresh.
• mxDoc.getActiveView().refresh()

30
Getting data
Document (.mxd file)
Map
AttributeTable
FID Data
1 234
2 875
Layer
Feature
234
Values
31
Summary

• Get the Applications Document.
• Get the Maps from it.
• Pick the one you want or loop through them.
• Get a Layer from the Map, or Loop through all of
  them.
• Generate an Attribute table and use Rows / Fields
  to get data.
• Or use the Layers search routine to search for
  Features.

32
Next Lecture

• Editing data.
• External applications.
• Practical
• Building a Toolbar.
• Getting and sorting data.