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Dr. Jim Mitchell, DOTD Joshua Kent, LAGIC LA GIS Council Presentation January 20, 2005

Louisiana’s Spatial Domain or Everything you’ve ever wanted to know about Geospatial Domains & Coordinate Precision, but were afraid to ask. Dr. Jim Mitchell, DOTD Joshua Kent, LAGIC LA GIS Council Presentation January 20, 2005. The Geodatabase.

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Dr. Jim Mitchell, DOTD Joshua Kent, LAGIC LA GIS Council Presentation January 20, 2005

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  1. Louisiana’sSpatial Domainor Everything you’ve 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 ESRI’s ArcGIS. • The Geodatabases is a relational database that stores geographic data. • Two Types of Geodatabases • Personal (for the desktop) • Enterprise (for an DBMS) Louisiana's Spatial Domain

  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 Louisiana's Spatial Domain

  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. Louisiana's Spatial Domain

  5. Geographic Coordinate System Projected Coordinate System Illustrates the 3D shape of the Earth Illustrates a 3D surface on a 2D surface 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). Louisiana's Spatial Domain

  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. Louisiana's Spatial Domain

  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 ... Louisiana's Spatial Domain

  8. 2,147,423,647 2,147,423,647 0 0 OFF LIMITS Example: Spatial Domain • All GIS Features Must Fit Within this Positive, 32-bit Integer Space. The Database’s Spatial Domain Louisiana's 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. Louisiana's Spatial Domain

  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. Louisiana's Spatial Domain

  11. X = 123.456789Precision =1000 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) Example: Coordinate Precision • Precision is a Scale Factor • Used to preserve decimal places before rounding • Larger precision preserves more digits Louisiana's Spatial Domain

  12. Coordinate System Units Precision Storage Units = Example: Precision Preservation Louisiana's Spatial Domain

  13. Don’t Look... It’s 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. Louisiana's Spatial Domain

  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. Louisiana's Spatial Domain

  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. Louisiana's Spatial Domain

  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. Louisiana's Spatial Domain

  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, -91.9826443or+30.319, -91.983 Louisiana's Spatial Domain

  18. Coordinate System UnitsEquipment Resolution(Desired Precision) Precision = 1. Calculating Precision *The smallest value for precision is 1 Louisiana's Spatial Domain

  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 it’s been defined. Louisiana's Spatial Domain

  20. Someone Else’s Job... Isn’t someone responsible for creating a standardized Spatial Domain and Coordinate Precision for Louisiana? YES... Louisiana's Spatial Domain

  21. Louisiana’s 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 Louisiana's Spatial Domain

  22. Max X = 1,137,595.909 Max Y = 3,773,695.909 Precision = 2287.000 or 1/2287 meters Min X = 198,600.000Min Y = 2,834,700.000 Louisiana's Spatial Domain

  23. Max X = 1,137,595.909 Max Y = 3,773,695.909 Precision = 2287.000 or 1/2287 meters Min X = 198,600.000Min Y = 2,834,700.000 Louisiana's Spatial Domain

  24. But wait, there’s 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) Precision = 2287.000 or 1/2287 meters Min X = 198,600.000Min Y = 2,834,700.000 Louisiana's Spatial Domain

  25. Don’t Let this Happen To You! Don’t Loose Data Because it Falls Outside the Domain! Louisiana's Spatial Domain

  26. AS SEEN ONTV Get Your’s Today! • You too can have your very owncopy of the Louisiana Spatial Domain http://lagic.lsu.edu/mapserver Louisiana's Spatial Domain

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