Autodesk 15606-011408-9330 User Guide - Page 119

About Coordinate Precision, Choosing a Coordinate System, SDF Component Toolkit, or Autodesk Map

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About Coordinate Precision Coordinate precision is the level of accuracy at which a point can be stored and retrieved to match its original location. When you use the SDF Loader, SDF Component Toolkit, or Autodesk Map® to convert your data to an SDF, you can specify whether to use single (32-bit) precision or double (64-bit) precision. For latitude/longitude coordinates, single precision is accurate to about 16 feet or 5 meters, whereas double precision is accurate to better than a fraction of an inch or 1mm. Single precision is usually more than enough accuracy for most applications, but if you are creating very large-scale maps for applications that require that you accurately pinpoint items, you might need double precision. If you are using arbitrary XY coordinates and the base unit of the map is already very small (such as inches on a facilities management map of office equipment), single precision will probably be sufficient. For more information, refer to the Coordinate Precision White Paper at: http://www.autodesk.com/utilitypapers Choosing a Coordinate System If you do not know which coordinate system to use, or if you need to decide which coordinate system to use in your office or department, consider your options in this order:  Consult with the data engineer who provided your data.  Use the same coordinate system as other staff in your organization.  Use the same coordinate system as your most common data source.  Choose the coordinate system used by people who share data with you.  If the area is small, use the same coordinate system as your local city or county government. If the area is large, use the same coordinate system as the state, regional, provincial, or national mapping group.  Ask surveyors, cartographers, consultants, and other mapping profession- als for suggestions. Designing the Map | 119

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Designing the Map
|
119
About Coordinate Precision
Coordinate precision is the level of accuracy at which a point can be stored
and retrieved to match its original location. When you use the SDF Loader,
SDF Component Toolkit, or Autodesk Map
®
to convert your data to an SDF,
you can specify whether to use single (32-bit) precision or double (64-bit)
precision. For latitude/longitude coordinates, single precision is accurate to
about 16 feet or 5 meters, whereas double precision is accurate to better than
a fraction of an inch or 1mm. Single precision is usually more than enough
accuracy for most applications, but if you are creating very large-scale maps
for applications that require that you accurately pinpoint items, you might
need double precision. If you are using arbitrary
XY
coordinates and the base
unit of the map is already very small (such as inches on a facilities manage-
ment map of office equipment), single precision will probably be sufficient.
For more information, refer to the Coordinate Precision White Paper at:
Choosing a Coordinate System
If you do not know which coordinate system to use, or if you need to decide
which coordinate system to use in your office or department, consider your
options in this order:
Consult with the data engineer who provided your data.
Use the same coordinate system as other staff in your organization.
Use the same coordinate system as your most common data source.
Choose the coordinate system used by people who share data with you.
If the area is small, use the same coordinate system as your local city or
county government. If the area is large, use the same coordinate system as
the state, regional, provincial, or national mapping group.
Ask surveyors, cartographers, consultants, and other mapping profession-
als for suggestions.