WFM 6202: Remote Sensing and GIS in Water Management Akm Saiful Islam [Part-B: Geographic...

transcript

WFM 6202: Remote Sensing and GIS in Water Management

Akm Saiful Islam

[Part-B: Geographic Information System (GIS)]

Lecture-4(b): Geo-Database

December, 2008

Institute of Water and Flood Management (IWFM)Bangladesh University of Engineering and Technology (BUET)

WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful IslamInstitute of Water and Flood Management (IWFM) , Bangladesh University of Engineering and Technology (BUET)

Lecture Topic

• Understand basic Geodatabase concepts and structure

• Know the advantages in using the Geodatabase format

• Managing a GeoDatabase

• Creating GeoDatabase

First Generation Storage/Linking

AS400Database

Access Database

Tabular Data Spatial Data

•Tabular/Spatial data is linked outside the database

•Links occur using unique IDs….Parcel Numbers

•Storage is still in separate locations

Second Generation Storage/LinkingGeodatabases

Tabular Data

Spatial Data

•Tabular/Spatial data is stored/linked in a single location!!

o Spatial & attribute data integrity

o Intelligent Behavior

o Centralized Data Storage

o Increased Performance

o Advanced Analysis Capabilities

o Multi-user editing (SDE format)

Benefits of a GeoDatabase

Benefits of Migrating to a GeodatabaseData Integrity

• Maintain tabular data more efficiently– Reduce typological

data errors

• Maintain spatial data more efficiently– Reduce spatial errors

Pro-West & Associates

What is a Geodatabase?

• A spatial and attribute data

container container – Relational database

management system (RDBMS)

– Maintains data integrity

– Apply Rules and Behavior

• Native data format for ArcGIS

Relational Database - A method of structuring data as collections of tables that are logically associated to each

other by shared attributes. Any data element can be found in a

relation by knowing the name of the table, the attribute (column)

name, and the value of the primary key.

2 Types of Geodatabase

• Personal GeodatabasePersonal Geodatabase– Stand alone PC, MS Access database– Supports individual and small groups on

moderate size datasets

• Enterprise GeodatabaseEnterprise Geodatabase– Exists on underlying RDBMS through Spatial

Database Engine (SDE) e.g. SQL Server– Usually runs on a dedicated server– Supports many users and massive datasets– Supports raster datasets

Two types of GeoDatabases

• Personal– Access

• Multi-user– SDE

GIS SQLSDEData Stora

Interpreter

View/Analyze

The Personal GeodatabaseIt’s not Scary!

• Stores spatial and tabular data in an Access database format

• Sets the stage for future SDE geodatbase migration

• Edit in ArcView, ArcEditor or ArcInfo

Geodatabase Features

• Contains tables, feature classes, feature datasets, topology rules, etc. Tables

Feature Classes

Topology

Feature Dataset

Feature data set

Feature class

Geometric network

Annotation class

Geodatabase ElementsGeodatabase

Relationship class

GeoDatabase (GDB) structure

• Stores– Feature datasets– Feature classes– Tables– Raster– More

• A unique structure within the GDB

Feature Dataset

• Contains Feature Classes – Must have same

coordinate system

• Required for Topology– Behavior

relationships between feature classes.

GDB Objects: Feature Dataset

• A collection of feature classes– Environment for spatial reference– Environment for topology – Environment for coincident geometry and linked

annotation– Feature classes inherit spatial reference

• Data loaded are projected on the fly, if necessary

Feature Class

• Stores a single feature type

– Point, Line, Polygon

• Can be standalone or member of a Feature dataset

Stand Alone

Feature DatasetFeature Class

GDB Objects: Feature Class (FC)

• A collection of features– Each feature class has one geometry type (point,

multi-point, line, polygon)• Can be stored in a feature dataset or ‘stand-alone’• Attributes are

stored with coordinate data in one table

Spatial Reference

Coordinate domain• Extent of available coordinates

– Min and max X,Y coordinates– Precision = storage units per

map unit• Example, 1000 mm per meter

• Make sure it covers study area– Allow for growth

• ArcCatalog default– Import: data plus room for growth

• Set your own– Import from existing data– Type in extent for study area

2.14 billion storage units

Domain

• A property of a feature dataset or feature class (cannot change once set)

Domains

• Spatial

• Attribute– Range of values (e.g., 0-100)– Coded values (e.g., 1 = potatoes 2 = wheat)

The Spatial Domain

• The Geodatabase stores all geometry coordinates as positive integers– Faster Display, Processing, and Analysis– Better Compression (DBMS only)– Efficient for managing topologic relationships

• Limited to 2,147,423,647 storage units.– 2.14x109 meters, or miles, or inches, or ...

Accuracy and Precision• Accuracy in the Data

– Scale of source map scale will determine accuracy*• 1:600 (1”=50’) ± 1.7 feet

• 1:1,200 (1”=100’) ± 3.33 feet

• 1:2,400 (1”=200’) ± 6.67 feet

• 1:4,800 (1”=400’) ± 13.33 feet

• 1:24,000 ± 40.00 feet– Precision

• Ability to store the accuracy– Significant digits

» Single precision 6-7 precise digits» Double precision 13-14 precise digits» Geodatabase 0-10 precise digits

Example: Spatial Domain

• All GIS Features Must Fit Within this Positive, 32-bit Integer Space.

OFF LIMITS

2,147,423,647 2,147,423,647

The Database’s Spatial Domain

Standard Fields• Feature classes have default fields

– ObjectID – unique identifier– Shape – contains coordinates of feature– Area – automatically calculated and maintained for polygons

• Shape_Area (Personal GDB)

– Length – automatically calculated and maintained for lines and polygons

• Shape_Length (Personal GDB)

Spatial Reference

• Property of a feature class or feature dataset• Components

– Coordinate system– Coordinate domain

• Permanent after definition is saved– Warning: it may look like you changed the coordinate

system, but you can’t and don’t try. It messes things up!

• See next slide for more information

Storing Feature Coordinates

Two important considerations when storing

feature coordinates in a Geodatabase:

1. All data is stored as positive, 32-bit integers (Spatial Domain)

2. All data must maintain a Coordinate Precision.

Coordinate Precision

• The geodatabase converts all coordinates into 32-bit Storage Units.

• Storage Units are the smallest measurable unit that can be stored in a Geodatabase.

• Precision is used to convert coordinate system units into storage units.

Example: Coordinate Precision

Floating Point Coordinate in ArcGIS

(123.456000)

Multiply by Precision

123.456789 × 1000

Divide by Precision 123456 ÷ 1000

Integer Storage Unit in a Geodatabase

(123456)

X = 123.456789Precision =1000

• Precision is a Scale Factor– Used to preserve decimal places before

rounding– Larger precision preserves more digits

Example: Precision Preservation

Coordinate system units ÷ Precision = Storage units

Meters 100 1 cm

Meters 1000 1 mm

Meters 50 2 cm

Feet 12 1 inch

Coordinate System Units PrecisionStorage Units =

Topology Objects

• Maintain data integrity– Within feature class– Between feature class

• Feature Dataset required

• Functionality– Display Topology

Errors– Select and Correct

Errors– Validation

• Regarding map features, topology is relationship between features connectivity and adjacency.

• Geodatabase topology provides tools to ensure integrity of spatial data.

Selected Topology Rules

• 25 available 25 available topology topology rulesrules

• 2 Rules 2 Rules currently currently appliedapplied

– Must Not Overlap

– Must Not Have Gaps

File Management

• Compacting the Personal Geodatabase– Reduces file size

• Procedure– In ArcCatalog, right

click on the .mdb file– Select the Compact

Database option in the context menu

Reference Data Locations

• Proscribed by the Standard for Geospatial Dataset File Naming– http://dlnt20.fsa.usda.gov/scdm/DP/Parent3.htm

• Standard folder structure on shared f: drive

• GeodataGeodata – top level geospatial data folder

• Local Geodata Administrators have authority to create, delete, and change folders, but only as outlined in the standards document.

<disk drive>:geodata

soils <geospatial dataset category (directory / folder)>

soil_a_ks057

topographic_images <geospatial dataset category (directory / folder)>

plants

soil_p_ks057

soil_l_ks057

• The current standard has 23 common geospatial dataset categories such as soils that consist of 1 or more geospatial datasets.

Data Management File Naming Standards

A geospatial dataset file name should:

• be less than 30 characters long

• consist of lower case a-z and numerals 0-9• first character always a-z

soil_a_ks057

• Elements of a file name

Feature category Feature type: a-polygon, l-line,

p-point, t-table, i-image, etc.

Data Management File Naming Standards cont.

Location: Alpha or numeric FIPS code

Data Storage and Backup

• Shared data in a service center must be on the f: drive.• Personal data can be stored on the c: drive or h: drive.

– c: drive is notis not routinely backed up.– h: drive should contain important working files

that can be routinely backed up.• Local Geodata Administrators are responsible for

ensuring backups are routinely being made of specific directories.– Large, easily replaced datasets should not be

routinely backed up because they can be obtained again.

– Files and directories that change regularly should be routinely backed up.

GDB Design

• A critical step• UML modeling for

ArcGIS– IBM Rational Rose– MS Visio

• Class diagrams

Managing Your GDB

• ArcCatalog is your main tool to manage the schema– Construction of component parts– Organization of those parts– Properties for the parts

• Many capabilities are available– Some are not on the default GUI

Reading Schemas

Structural

Logical

Most data access technologies provide a way for you to query the schema of a database, and obtain information about the tables, stored procedures, data types, users, and other content of a database.

Creating a GDB

• Personal– Use ArcCatalog

• Multi-user– Must be done at the

system level

1.1. Open ArcCatalog Open ArcCatalog 2.2. Choose a folder Choose a folder

location location 3.3. Right click: Choose Right click: Choose

New < Personal New < Personal GeodatabaseGeodatabase

Creating a new personal geodatabase

Right click your geodatabase

Choose: New < Feature Dataset

Creating Feature Datasets

Creating an empty feature class

• Two locations available: stand-alone and within a feature dataset

Creating a feature dataset

Right click your geodatabase

Choose: New < Feature Dataset

Creating Feature Datasets

Feature Datasets: Setting the spatial reference

http://arcscripts.esri.com/ :Search on Spatial Domain

1. Set the Projection

2. Set the Domain

• Precision

• Extent

Import existing data

•Navigate to the feature dataset or geodatabase icon in ArcCatalog

•Right Click•Choose Import

Use this to import any existing format!

Subtypes & Domains

Subtype:

•Distinguish features within a single layer

•Maintain different domains within the same field

•Need ArcEditor or ArcInfo

Domain:

•Identify & constrain attribute values

•Can utilize in ArcView

Subtypes & DomainsParcels

Example

Subtype: Boundary Line

Domains: ROW Type

Subtypes

• Must be long or short integer fields

• Created in ArcEditor or ArcInfo

• Increases the efficiency of the editing process

• Use when

– Standardizing a legend

– distinguishing different default values/domains within the same field

Creating Subtypes

• In ArcCatalog• Double click on a feature

class• Select the Subtype tab

Creating Domains

Created inArcCatalog

1. Double Click on the Personal Geodatabase Icon

2. Choose the Domains tab

Creating Domains—Assigning to Feature Classes

In ArcCatalog

1. Double click a feature class

2. Choose the Fields tab

3. Highlight a field

4. Click Domain under the Field properties section

Creating Domains—Assigning default values

Set in the Field Properties section

Using Domains during the Editing Process

Geodatabase TopologyPutting the power into your hands

– Topology Rules• Preset rules to define topological relationships to

ensure connectivity, adjacency and coincidence– Can be changed at any time

– Topology Tools• Maintain spatial relationships• Toolbar and Tasks

Creating Topology

1. Rules– Land use boundaries overlap parcel boundaries– Manholes overlap sanitary line endpoints

2. Cluster Tolerance– Min distance where vertices within tolerance are

snapped

3. Ranks– Control what features move during validating

• Surveyed points will not move (snap) during the validation process

Validating Topology

• Validate edited features using set topology rules

• Evaluate rules/tolerance and generates error notifications

• Snaps vertices using set cluster tolerance and ranks

Create a New Topology

• Created in ArcCatalog

• Created within a Feature Dataset

• Topology Wizard – Allows user to set Rules, Ranks,

Tolerance, and perform initial Validation

Final Topology

When added to ArcMap, will show errors from the validation process

Managing Topologies

• Right click on the Topology in ArcCatalog

Topology ToolsMaintenance

• Standard toolbar in ArcView-ArcInfo

• Used in an editing environment in ArcMap

• Use in conjunction with Topology Tasks in Editor Toolbar

Editor ToolbarMaintenance

• Topology Tasks: Modify, Auto Complete Polygon and Reshape

– Allows user to use basic editing tools to alter vertices, replace lines, add adjacent polygons or alter existing polygons

– Use in conjunction with the Topology Edit Tool on the Topology Toolbar

Remember:Set snapping and snapping tolerance

Flexible Editing• Topology edit tool

– Allows for editing shared boundaries– Builds a temporary topology cache within a

given extent• Faster performance• Must use each time your extent changes

• Show shared features tool– Move a boundary without effecting shared

boundaries (temporary)• Parcels & land use • Parcels and easements

Validate & Fix

• Validate after editing is complete– Errors are highlighted

• Click the Fix Error button

• Select a feature and right click– Fix– Mark as an Exception– Do Nothing

Process in Review

1. Plan for success

2. Import data

3. Set Subtypes & Domains

4. Create Topology

5. Start editing!

• Projecting data– Must create a new feature class

• PGDB is 2 GB max

• Read-only on a PGDB will restrict some analyses, such as Select by Location

• Use compact to clean up temporary files

• All table names need to be unique

• Create a Personal GDB

• Create an empty Feature Class

• Create a Feature Dataset

• Create a Feature Class within the Feature Dataset

WFM 6202: Remote Sensing and GIS in Water Management Akm Saiful Islam [Part-B: Geographic...

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