Louisianas Spatial Domain or Everything youve ever wanted to know about Geospatial Domains

1
LouisianasSpatial Domainor Everything youve
ever wanted to know about Geospatial Domains
Coordinate Precision,but were afraid to ask.

• Dr. Jim Mitchell, DOTD
• Joshua Kent, LAGIC
• LA GIS Council PresentationJanuary 20, 2005

2
The Geodatabase

• The Geodatabase is a data format used within
  ESRIs ArcGIS.
• The Geodatabases is a relational database that
  stores geographic data.
• Two Types of Geodatabases
• Personal (for the desktop)
• Enterprise (for an DBMS)

3
Geodatabase Structure

• A Container for Managing GIS Data Objects
• Features (shape, line, polygon)
• Feature Datasets (topologically related feature
  classes)
• Non-spatial Tables (attribute data)
• All Feature Objects are Spatially Referenced

4
Spatially Referenced Data

• We use a Reference System to determine the
  location of features on Earth or on a map.
• In a GIS, the reference systems used to determine
  feature locations are called Coordinate Systems.

5
Coordinate Systems

• Two Types of Coordinate Systems
• GEOGRAPHIC used to locate objects on the curved
  surface.
• PROJECTED used to locate objects on a flat
  surface (i.e. paper, computer screen).

6
Storing Feature Coordinates

• Two Important Considerations when Storing
• Feature Coordinates in a Geodatabase
• All data is stored as positive, 32-bit integers
  (i.e. Spatial Domain)
• All data must maintain a Coordinate Precision.

7
1. 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 arpents,
  or ...

8
Example Spatial Domain

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

The Databases Spatial Domain
9
Storing Feature Coordinates

• Two important considerations when storing
• feature coordinates in a Geodatabase
• All data is stored as positive, 32-bit integers
  (Spatial Domain)
• All data must maintain a Coordinate Precision.

10
2. 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.

11
Example Coordinate Precision

• Precision is a Scale Factor
• Used to preserve decimal places before rounding
• Larger precision preserves more digits

12
Example Precision Preservation
13
Dont Look... Its Magic!

• Spatial Domain and Precision Values Will Be Set
  Automatically
• Spatial Domain and Precision will be defined by
  the first feature class imported.
• Automatic Settings Are Bad
• Errors can occur when importing features into a
  Feature Dataset.
• Values must be set deliberately to guarantee a
  specific precision.

14
Why is this so important?

• Data Management
• Larger Domains will support larger geographic
  areas.
• Larger Domains are maintained at the expense of
  precision.
• Topology
• Topology defines the relationship one feature
  class has with another.
• Topology Efficient Data Management
• Example Modifying the border of one feature
  class simultaneously modifies the borders of
  other feature classes.

15
Why else is this important?

• Data Sharing
• A standardized Spatial Domain Coordinate
  Precision ensures that all features can be shared
  by all parties without impacting accuracy.
• Understanding your Data
• Understanding the relationship your data shares
  with its environment.
• Understanding the level of precision at which
  your data was collected/created.

16
The Zen Art of Geodatabase Design

• Become One with your Data!
• Learn how to modify your Spatial Domain
• Define your Coordinate Precision
• Translate floating point coordinates into integer
  storage units
• Define your Spatial Extents
• Identify the maximum spatial extents for all your
  data without exceeding the 2.147 billion integer
  storage units.

17
1. Calculating Precision

• Store Precision Based on Data Quality
• Match storage units to equipment resolution
• Not all floating-point digits will represent
  actual data
• How Precise is your GPS?
• 30.3192129, -91.9826443or30.319, -91.983

18
1. Calculating Precision
The smallest value for precision is 1
19
2. Define the Spatial Domain

• Spatial Domain Max Spatial Extents
• Cannot exceed 2,147,483,647 storage units (or
  231-1)
• Cannot change once its been defined.

20
Someone Elses Job...

• Isnt someone responsible for creating a
  standardized Spatial Domain and Coordinate
  Precision for Louisiana?
• YES...

21
Louisianas Spatial Domain

• Developed For the LA GIS Council
• Encompasses Louisiana and Surrounding Areas
• Maintains High Level of Precision (.0004 meters)
• Characteristics
• UTM Coordinate System, Zone 15
• North American Datum 1983
• Meter Units
• 0.4mm precision

22
Max X 1,137,595.909 Max Y 3,773,695.909
Min X 198,600.000 Min Y 2,834,700.000
Precision 2287.000 or 1/2287 meters
23
Max X 1,137,595.909 Max Y 3,773,695.909
Min X 198,600.000 Min Y 2,834,700.000
Precision 2287.000 or 1/2287 meters
24
But wait, theres more...
Max X 1,137,595.909 Max Y 3,773,695.909
Z Domain Range of Altitude Values (-500000 to
1647483.65 meters at 1/1000 meter precision) M
Domains Range of Linear Referenced Values(0 to
21474.84 meters at 1/100000 meter precision)
Min X 198,600.000 Min Y 2,834,700.000
Precision 2287.000 or 1/2287 meters
25
Dont Let this Happen To You!
Dont Loose Data Because it Falls Outside the
Domain!
26
Get Yours Today!

• You too can have your very owncopy of the
  Louisiana Spatial Domain
• http//lagic.lsu.edu/mapserver