Survey foot and International foot

There are various units of linear measurement in use. Foot is also among one of them.

A foot is not an SI unit of length and hence its size slightly varies from system to system, such as English units, Imperial units, and United States customary units. The most commonly used foot today is the International Foot.

In this blog I am going to describe US survey foot and International Foot and how MicroStation user can set them for the design files.

International Foot :-

 It was defined in 1959. It is the most commonly used representation.

1 International Foot = 1/3 yard = 0.3048 meters

1 International Foot = 12 Inches

 In MicroStation “Feet” represents International Foot. To set Working Units as International Foot, open Design File Settings and select Feet in Master Unit drop-down list.

Survey Foot :- 

                Prior to 1959, Survey Foot was the most prominent unit of linear measurement in US.  It is almost equal to International Foot, but its definition is slightly different:

  • International Foot: 0.3048 meters
  • US Survey Foot: 1200/3937 meters

This small difference can cause problems in some cases when the area under measurement is large like in mapping etc., so it is advisable to always know which units are being used.

These two units have the following relationship in terms of numeric value.

1 International Foot = 0.999998 U.S. Survey Foot

1 U.S. Survey Foot = 1.000002000004000008000016000032 International Foot

In MicroStation to set working units as US Survey Foot , the steps are common as for setting up any unit, just  go to Design File Settings and in Master Unit drop down list select US Survey Feet and click OK. As shown in the snap shot.

Feet used in MicroStation in the standard unit list are based on International Foot definition and not on US Survey Foot definition. This is the correct definition for most work outside of the civil engineering and surveying disciplines. Many states continue to base their survey work on the US Survey Foot. One must verify the basis of the survey for projects to ensure the work is on correct units of measurement.

Additional information regarding this is in The difference between US Survey Foot and International Foot wiki article.

More blogs are coming up so be there...

 

Anonymous