Units of Measure

ERDAS IMAGINE Help

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Units of measure are expressed in numerous functions throughout ERDAS IMAGINE. For example, these units are expressed in places such as measuring a line drawn in an image in the View, recalculating elevation values, or if you are looking at the Rectangle Properties dialog of an AOI in an image. This document defines the units of measure used in ERDAS IMAGINE.

Units of measure are categorized into angle, distance, area, volume, and time. For a complete list of valid strings used in the tables below for <units1>, see the file <$IMAGINE_HOME>/etc/units.dat.

reference_icon You can edit the units.dat text file to add a desired unit. See Add New Units of Measure.

Angle

Conversion column lists the formula to convert a numeric value from your selected unit to the IMAGINE standard internal unit. Radian is the standard internal unit used when measuring angles.

Unit

<units1>

Symbol

Conversion to radians

<standardunits>

Definition

radian

rad

1.0

units_eqn_radian

decimal degrees

dd

combination of latitude/longitude degrees, minutes, and seconds converted into a decimal fraction, expressed as degrees

decimal minutes

dm

units_eqn_decimal_minutes

In latitude/longitude, minutes value converted into a decimal

decimal seconds

ds

units_eqn_decimal_seconds

In latitude/longitude, seconds value converted into a decimal

degree

deg, dg

units_eqn_degree

plane angular degree

grad

grad

units_eqn_grad

100 grads in a 90 degree angle, 1 grad = 0.9 of a degree or of a radian. Measurement of an arc in metric system.

gon

gon

units_eqn_grad

Same as grad. The term gon is used in European countries where grad means degree.

Convert the value <value> from <units1> to the same amount expressed in <standardunits>.

<units1> is the expression in Unit column, <standardunits> is the expression derived after conversion.

Example: 2 degrees = 0.034906 radians (to 6 places)

Distance

Conversion column lists the formula to convert a numeric value from your selected unit to the IMAGINE standard internal unit. Meter is the standard internal unit used when measuring distance.

Metric Units

Unit

<units1>

Symbol

Conversion to meters

<standardunits>

Definition

meter

m

1.0

Basic SI* unit of length or distance

centimeter

cm

<value> * 0.01

100 centimeters = 1 meter

millimeter

mm

<value> * 0.001

1000 millimeters = 1 meter

kilometer

km

<value> * 1000.0

1 kilometer = 1000 meters

nanometer

nm

<value> * 0.000000001

1 meter = units_eqn_10_9th nanometers

micron

units_eqn_micron

<value> * 0.000001

1 meter = units_eqn_10_6th microns

micrometer

units_eqn_micron

<value> * 0.000001

1 meter = units_eqn_10_6th micrometers

other

1.0

standard internal unit (meter) or if unit is unknown

* International System of Units (abbreviated SI from the French name Le Système International d'Unités)

Convert the value <value> from <units1> to the same amount expressed in <standardunits>.

Example: 25 kilometers = 25,000 meters

U.S. Survey Foot Units

Conversion column lists the formula to convert a numeric value from your selected unit to the IMAGINE standard internal unit. Meter is the standard internal unit used when measuring distance.

Unit

<units1>

Symbol

Conversion to meters

<standardunits>

Definition

us survey feet

us survey foot

ft

<value> * 0.3048006096012192

units_eqn_us_survey_foot

1 meter = 3.2808333 U.S. survey feet

feet

foot

ft

<value> * 0.3048006096012192

units_eqn_us_survey_foot

1 meter = 3.2808333 U.S. survey feet

Convert the value <value> from <units1> to the same amount expressed in <standardunits>.

Example: 200 U.S. survey feet = 60.9601 meters (to 4 places)

International Foot Units

Conversion column lists the formula to convert a numeric value from your selected unit to the IMAGINE standard internal unit. Meter is the standard internal unit used when measuring distance.

Unit

<units1>

Symbol

Conversion to meters

<standardunits>

Definition

international feet

international foot

<value> * 0.3048

1 international foot = 0.3048 meters

1 meter = 3.2808398 international feet

inches

inch

in

<value> * 0.3048006096012192 / 12.0

1 inch = 2.54 centimeters

1 meter = 39.3700787 inches

point

pt

<value> * 0.3048 / 12 / 72.0

Intended for map compositions. A measurement unit for font sizes in paper units.

units_eqn_point_on_paper

device pixel

<value> * 0.3048 / 12 / 300.0

Intended for map compositions. A measurement unit for printer devices. Default assumes a device resolution of 300 dpi.

yard

yd

<value> * 3 * 0.3048

1 yard = 3 feet

mile

mi

<value> * 5280 * 0.3048

A unit of length defined to be exactly 5,280 feet.

1 mile = 5,280 feet

1 mile = 1609.3472 meters (to 4 places)

Convert the value <value> from <units1> to the same amount expressed in <standardunits>.

Example: 3 miles = 4828.032 meters

Variants

Conversion column lists the formula to convert a numeric value from your selected unit to the IMAGINE standard internal unit. Meter is the standard internal unit used when measuring distance.

Unit

<units1>

Conversion to meters

<standardunits>

modified american foot

<value> * 0.3048122530

clarke foot

<value> * 0.3047972651

indian foot

<value> * 0.3047995142

link

<value> * 0.2011661950

benoit link

<value> * 0.2011678249

clarke link

<value> * 0.2011661949

sears link

<value> * 0.2011676512

benoit chain

<value> * 20.1167824944

sears foot

<value> * 0.30479947153867620

benoit chain 1895 a

<value> * 20.1167824

benoit chain 1895 b

<value> * 20.1167824944

sears chain

<value> * 20.1167651216

sears yard
sears yd

<value> * 0.9143984146

indian yard
indian yd

<value> * 0.9143985425

fathom

<value> * 1.8288000000

international nautical mile

<value> * 1852.0

gold coast foot

<value> * 0.3047997101815088

Convert the value <value> from <units1> to the same amount expressed in <standardunits>.

Example: 3 fathoms = 5.4864 meters

Area

Conversion column lists the formula to convert a numeric value from your selected unit to the IMAGINE standard internal unit. Hectare is the standard internal unit used when measuring area.

Unit

<units1>

Symbol

Conversion to hectares

<standardunits>

Definition

hectare

1.0

1 hectare = 10,000 square meters.

Equivalent to 2.471 acres in the English system.

acre

<value> * 0.4046856

Defined as 10 square chains (1 chain = 4 rods or 66 feet)

1 acre = 43,560 square feet

1 acre = approximately 4047 square meters

square mile

sqmile

units_eqn_mile_sq

<value> * 258.9988

Area of a plane surface enclosed by a square with each side 1 mile in length.

1 sq mile = approximately 640 acres

square nautical mile

sqnautical mile

<value> * 342.9904

Area of a plane surface enclosed by a square with each side 1 international nautical mile in length.

square foot

sqfoot

sqfeet

units_eqn_foot_sq

<value> * 0.00000929030

Area of a plane surface enclosed by a square with each side 1 foot in length.

square meter

sqmeter

units_eqn_meter_sq

<value> * 0.0001

Area of a plane surface enclosed by a square with each side 1 meter in length.

square kilometer

sqkilometer

units_eqn_kilometer_sq

<value> * 100

Area of a plane surface enclosed by a square with each side 1 kilometer in length.

Convert the value <value> from <units1> to the same amount expressed in <standardunits>.

Example: 56 square meters = 0.0056 hectares

Volume

Conversion column lists the formula to convert a numeric value from your selected unit to the IMAGINE standard internal unit. Liter is the standard internal unit used when measuring volume.

Unit

<units1>

Symbol

Conversion to liters

<standardunits>

Definition

liter

lt

1.0

Metric unit of capacity equal to volume of 1 kilogram of water at  4 degrees C (39 degrees F) and at standard atmospheric pressure of 760 mm of mercury.

milliliter

ml

<value> * 0.001

1 liter = 1000 ml

gallon

gal

<value> * 3.7854118

Volume used in liquid measure equal to 4 quarts or approximately 3.785 liters.

cubic foot

units_eqn_foot_cubic

<value> * 28.3169

Volume occupied by a cube with each side 1 foot in length.

1 cubic foot = 28,316.8 cubic centimeters

cubic meter

units_eqn_meter_cubic

<value> * 1000

Volume occupied by a cube with each side 1 meter in length.

1 cubic meter = 1000 liters

cubic kilometer

units_eqn_kilometer_cubic

<value> * 1000000000000

Volume occupied by a cube with each side 1 kilometer in length.

Convert the value <value> from <units1> to the same amount expressed in <standardunits>.

Example: 4 gallons = 15.1416472 liters

Time

Conversion column lists the formula to convert a numeric value from your selected unit to the IMAGINE standard internal unit. Second is the standard internal unit used when measuring time.

Unit

<units1>

Symbol

Conversion to seconds

<standardunits>

Definition

second

sec

1.0

Basic SI* unit of time. 1/60 of a minute of time.

minute

<value> * 60.0

1 minute = 60 seconds. 60 minutes = 1 hour.

hour

hr

<value> * 60.0 * 60.0

1 hour = 60 minutes. 24 hours = 1 day.

day

<value> * 24.0 * 60.0 * 60.0

1 day = 24 hours. 365.25 days = 1 year.

year

yr

<value> * 365.25 * 24.0 * 60.0 * 60.0

1 year = 365.25 days.

* International System of Units (abbreviated SI from the French name Le Système International d'Unités)

Convert the value <value> from <units1> to the same amount expressed in <standardunits>.

Example: 4 days = 345,600 seconds