What is a Foot Survey Feet vs. International Feet

1
What is a Foot?Survey Feet vs. International
Feet
Dan Ahern, PE
2
What are Models

• Drawing container inside a DGN file.
• All models in a DGN file are independent of each
  other.
• Graphics
• Working Units
• Views
• Exception all models in a DGN file share common
  color table and level definitions.

3
Using Models

• All DGN files contain at least one model.
• File Models to create a new model.

4
Types of Models

• Design Model
• A two-dimensional or three-dimensional drawing
  environment similar to a design file or .dgn file
  in MicroStation/J.
• Sheet Model
• A two-dimensional drawing environment for laying
  out plot sheets.

5
Models with GEOPAK and InRoads

• Limited support
• InRoads reads and writes to the active model.
• GEOPAK reads and writes to the active model for
  interactive processes.
• GEOPAK read from all models for batch processes
  such as create cross sections.

6
Working Units

• Define the real world
• size and measurement unit
• of the MicroStation drawing area.

7
Working Units in MicroStation/J

• Defined Master Unit Sub Unit Positional Unit
• Divides integer gridinto drawing space.
• All element verticeslocated at a PUgrid
  position.(controls drawing precision)

8
Working Units in MicroStation V8

• Defined Master Unit Sub Unit Resolution Unit
• Relates user selectedunits to MicroStationintern
  al unit (meter).
• Have no impact ondrawing precision.

9
Setting MicroStation V8 Units

• Select desired Master Unit and Sub Unit from the
  selection lists.
• Contents of Selectionlist defined in units.def
  file.
• Labels used forDimensioning.

10
Feet?

• The default Feet unit in MicroStation V8 is an
  International Foot.
• Survey Feet are activated through the units.def
  file.

11
What is a Survey Foot?

• History of the foot
• U. S. Metric Law of 1866
• 1 foot 1200/3937 m ? .3048006 m
• 1959 Adjustment of the Law
• 1 foot .3048000 m
• Result
• Old definition referred to as a US Survey Foot
• New definition referred to as an International
  Foot

12
Why does it matter?

• MicroStation V8 stores everything in meters.
• Converted to Master Units on the fly when any
  value is entered.
• Converted from Master Units on the fly for
  display.

13
Why does it matter?

• Short distances
• US Survey Foot International Foot (measured
  1/100 of a foot)
• At 100,000 feet
• Definitions result in a difference of about .2
  feet
• At 1,000,000 feet
• Definitions result in a difference of about 2
  feet
• At 10,000,000 feet
• Definitions result in a difference of about 20
  feet

14
Activating Survey Feet in MicroStation

• Edit the text file /Workspace/System/Data/units.d
  ef.

15
Units.def file

• Uncommented units will appear in the MicroStation
  interface.
• Labels at the beginning of each unit are used to
  match Master Units when converting a file from V7
  to V8.
• By default, V7 files with a MU of ft will convert
  to International Feet.

16
Converting V7 to V8

• MicroStation V8.0 or V8.1
• Method 1 If a MicroStation V7 file is converted
  to MicroStation V8 and the Master Unit in the V7
  file matches one of the label units for the
  survey foot in the units.def file, the working
  units in the MicroStation V8 file are
  automatically set to Survey Feet.
• Method 2 An existing MicroStation V8 file is
  updated to the Survey Foot working unit by
  issuing the keyin set units Survey Feet
• CAUTION Method 2 will not work for GEOPAK
  users.

17
Converting V7 to V8

• MicroStation 2004
• Method 1 If a MicroStation V7 file is converted
  to MicroStation V8 and the Master Unit in the V7
  file matches one of the label units for the
  survey foot in the units.def file, the working
  units in the MicroStation V8 file are
  automatically set to Survey Feet.
• Method 2 Select Working Unit from DGN File
  Settings dialog box.
• Method 3 An existing MicroStation V8 file is
  updated to the Survey Foot working unit by
  issuing the keyin set units Survey Feet
• CAUTION For GEOPAK users, method 2 also
  requires setting the resolution unit and method 3
  will not work.

18
Resolution Unit

• Defined on the Advanced Unit Settings dialog box.
• Determines the worst case accuracy of the drawing
  space at the outer reaches of the drawing space.
• Changing the resolution unit, changes the size of
  existing graphics in the model.

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Resolution Unit and GEOPAK

• GEOPAK references the Resolution unit to the
  GEOPAK preference unit.
• The GPK file does not have a unit.
• The GEOPAK preferences define the design unit.
• The GEOPAK preference unit, and MicroStation
  Resolution unit, and MicroStation Master unit
  must be the same!