Transcript Lecture 10
GTECH 361 Lecture 10 Behavior and the Geodatabase Rules and Behavior ..is what makes geodatabase features smart Enforcing integrity with attribute domains Grouping features using subtypes Table relationships Between feature classes Between feature classes and non-spatial tables Attribute Domains Define what values are allowed for a field in a feature or a non-spatial table Created and edited in ArcCatalog Attribute Domains Are a specialization of well-known data types ValveTypeDomain is a Long Integer with a permissible value range from 1..10 Enforcing Data Integrity Preventing errors during data entry Checking validity after the fact Types of Attribute Domains Range domains Coded value domains Split and Merge Policies Use attribute domains to specify how attributes are handled after the split or merge Manage attributes that will be affected by edits to a feature's geometry Split Policies Duplicate Default value Geometry ratio Merge Policies Default value Sum Weighted average Field Type Limitations to Split and Merge Policies Merge Policy Options Field Types Split Policy Options Coded Value Domain Date, double, float, long integer, short integer, text Default value, Duplicate Default value Range Domain Date, double, float, long integer, short integer Default value, Duplicate, Geometry ratio Default value, Sum values, Weighted average Subtypes The closest we get to object-orientation in the geodatabase To group similar features without creating a new feature class Group parcels into residential, commercial, and agricultural subtypes and associate different attribute domains with each group Faster than many feature classes Subtypes in ArcGIS Versions ArcView Only displays subtypes ArcEditor, ArcInfo Create, edit and use subtypes Example of a Subtype Subtypes of feature class country_lanes Example of a Subtype Subtype encoding and decoding Feature class table ArcMap Table of Contents Creating a Subtype Based on an existing attribute, or A new field containing subtype values Values have to be short or long integer For each subtype, you can associate default field values and domains You have to define one default type Once defined the new subtype can become target of an ArcMap edit operation Using Subtypes with Features Everything is Related… to everything else but… (Tobler’s Law) This multitude of relationships is usually not well captured in a GIS database Which makes tracking real-world situations difficult For instance… Cardinality Relationships Across Tables Relationship Definitions Require primary and foreign key to be of the same type Supported field types are short integer long integer float double text object ID Relationship Classes Permanently stored in the geodatabase Hence different from joins and relates in ArcMap, which are only stored in .mxd Within but not across geodatabase(s) Once created cannot be modified If corresponding table is deleted, the relationship class is deleted automatically Only 2 tables can be related per R.C. Relationship Properties Cardinality, origin and destination tables As discussed before Labels Relationship types and messaging Attributes Relationship Labels Relationship classes have forward and backward path labels Relationship Types Simple Table objects exist independently of each other Composite Destination objects cannot exist without an origin object Forward messaging only One-to-one or one-to-many cardinality Relationship Attributes Relationship classes can have attributes describing the relationship E.g, in a relationship between parcels and owners, an attribute of the relationship may be the percentage of ownership Relationship Classes, Relates and Joins Relationship Class Relate Join Typical Uses Modeling and editing Querying, Querying, labeling, related objects selecting symbolizing Referential Integrity Yes No No Messaging Yes No No Attributes Yes No No Relationship Yes Rules No No Cardinality All One-to-one, manyto-one All Relationship Rules Control how records in the origin and destination tables can be related Which objects or subtypes from the origin table can be related to which objects or subtypes in the destination table Specify a valid cardinality range for related objects or subtypes Relationship Rule Example Wood poles are able to support from 0 to 3 transformers, whereas steel poles support 0 to 5 transformers In Summary Modeling closer to real world by creating attribute domains, subtypes, and relationship classes Attribute domains define the allowable values Subtypes provide a way to implement different domains and relationships Relationship classes create a permanent record of their relationship (as opposed to join/relate) Relationship rules control which objects or subtypes from the origin table can be related to which objects or subtypes in the destination table 3-Dimensional GIS TINs, DEMs and 3-D Surfaces Surface Analysis in GIS Analyzing the distribution of a variable which can be represented as the third dimension of spatial data Elevation is a good example of a 3rd dimensional variable Most GIS packages represent z-values as an attribute of the data What is a DEM? DEM = digital representation of a topographic surface (usually a raster or regular grid of spot heights) DTM or digital terrain model = more generic term for any digital representation of a topographic surface, but not widely used DEM is the simplest form of digital representation of topography and the most common Resolution is a critical parameter Creating DEMs From contour lines (digital or scanned) scanning, raster to vector conversion + additional elevation data are (i.e. shorelines provide additional contours) algorithm is used to interpolate elevations at every grid point from the contour data Creating DEMs By photogrammetry (manually or automatically) extraction of elevation from photographs is confused when the ground surface is obscured e.g. buildings, trees DEMs from each source display characteristic error artefacts Background of TINs Developed in the early 1970's as a simple way to build a surface from a set of irregularly spaced points ….. .....Commercial systems using TIN began to appear in the 1980's as contouring packages, some embedded in GISs Surface Analysis in a Vector GIS Several ways of building a TIN are possible: from a set of irregularly-spaced points from points in a regular fashion - a lattice from digitized contours as line features Not usually practical to use polygon features The TIN Model Sample points are connected by lines to form triangles Each triangle's surface would be defined by the elevations of the three corner points Pros and cons of TINs TIN Construction From Points to Surfaces Exaggerating Elevations Terrain Analysis in Concert With Other GIS Operations Calculating Slope and Aspect From (raster) DEMs: to estimate these at a raster point, a 3x3 window centered on the point is usually used From TINs: simpler and more efficient, but perhaps not as accurate What Is Slope? Slope and Aspect Calculation Determining Drainage Networks A raster DEM contains sufficient information to determine general patterns of drainage and watersheds Flow direction determined by the elevations of surrounding cells Algorithms to determine the flow direction Water is assumed to flow from each cell to the lowest of its neighbors Flow Direction DEM Leading to Flow Accumulation Three Steps in Developing a Hydrological Model Flow Directions Accumulating Flow Critical Flow Level 2 Very Important Points Relief Shading Different Techniques for Visualizing Elevation 2D elevation raster Transparent hillshade Shaded relief map Main Uses of DEMs and TINs Determining attributes of terrain Finding features on the terrain elevation at any point, slope and aspect drainage basins and watersheds, drainage networks and channels, etc. Modeling of hydrologic functions energy flux and forest fires