Projection Information

The difference between NAD27 and NAD83 is that NAD 27 does not include Alaskan islands and Hawaii.

To convert from NAD27 to NAD 83

units feet

zone 3426

datum NAD27 NADCON

parameters

output

projection stateplane

units meters

zone 3426

datum NAD83 NADCON

parameters

end

WGS84 and NAD83 are essentially the same so it is not necessary to convert the datum.

There are a few possible units for geographic projection:

DMS: degrees, minutes, seconds indicated by DD MM SS (e.g. 10 30' 30" is listed as 10 30 30)

D: decimal degrees (e.g. 10.55)

DM: decimal minutes (e.g. 630.5)

DS:decimal seconds (e.g. 37830.0)

Other projections may also have these units:

meters

units per meter (real meter)

It is optional to state the datum to be used for all projections
except those which support data on a sphere only.

DATUM NONE

DATUM USER_DEFINED dx, dy, dz

The term name is simply means name of the datum. The term method is the datum conversion method used to convert between the specified datum (e.g. NADCON).

The classification none is used when projecting data on a spheroid
or sphere to a projection which supports data on a sphere only

You can also specify the spheroid to be used. However, do not use the SPHEROID subcommand if DATUM is stated in the parameters.

The default is Clarke 1866. AN other spheroid which can be used is GRS80. Look in Help "Map Projections " for a complete list of spheroids.

NOTE:ARC/INFO does not convert between spheroids unless transforming
between datums.

Here is a list of parameters for azimuthal projection.

units: ft or meters

parameters

radius of the sphere of reference

longtitude of center of projection

latitude of center if projection

false easting (meters)

false northing (meters):

The latitude of true scale is usually the Equator, but it doesn't
have to be. The radius of the sphere of reference must be a real number.
You should note that Azimuthal is supported
only on a sphere.

Here is a list of parameters for a conical projection.

projection lambert

units: feet

parameters

1st standard parallel:37 10 00

2

central meridian: -123 00 00

latitude of projection's origin:0 00

false easting: 0.0

false northing: 0.0

The longitude west of the Prime Meridian and the latitudes South
of the Equator are negative. The false easting and northing are
real numbers and can be zero. The latitude of origin defines the
origin of the y coordinate for the projection.

Here is a list of parameters for a cylindrical projection

projection cylindrical

units: feet

xhsift:100000000

yshift:2000000

parameters

longtitude of central meridian:171 0 0

latitude of standard parallel:-44 0 0

azimuth:45.0000

scale factor:1

The longitude west of the Prime Meridian and the latitudes South
of the Equator are negative. The azimuth must be entered as an
angle in decimal degrees. The scale factor of the central line
is a real number, usually one.

Each UTM zone has its own central meridian and spans 3 degrees
west and 3 degrees east. There are 60 zones. You can look in the
HELP in ARC under the Map Projection for a table with all the
zones and their spans.

The following projection file, called alb_lamb.prj, converts from
Albers projection to a Lambert Projection

projection albers

units meters

spheroid CLARKE1866

parameters

29 30 0.000

45 30 0.000

-96 0 0.000

23 0 0.000

0.00000

0.00000

output

projection lambert

units meters

spheroid GRS1980

parameters

27 25 0.000

34 55 0.000

-100 0 0.000

31 10 0.000

1000000.00000

1000000.00000

end

Another example is the following file, called geostate.prj, which
converts from geographic coordinates to stateplane.

projection geographic

units ds

zunits meters

datum NAD83

spheroid GRS1980

parameters

output

projection staeplane

units feet

zunits feet

datum NAD27

spheroid CLARKE1866

zone 5376

parameters

END

Go to Dr Maidment's Home Page