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

**projection stateplane
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:

**radians
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:

**feet
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 name{method}
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.

**projection azimuthal
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**

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

**input
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.

**input
projection geographic
units ds
zunits meters
datum NAD83
spheroid GRS1980
parameters
output
projection stateplane
units feet
zunits feet
datum NAD27
spheroid CLARKE1866
zone 5376
parameters
END**

*These materials may be used for study, research, and education, but
please credit the authors and the Center for Research in Water Resources,
The University of Texas at Austin. All commercial rights reserved. Copyright
1997 Center for Research in Water Resources.*