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Problem: Projector sample extension produces different results than ArcInfo PROJECT command

Description

The example in this article shows how to reduce the differences between the output of the Projector sample extension and the ArcInfo PROJECT command.

Cause

This is related to mismatches in either spheroid, datum, or both. When projecting in ArcInfo, the default spheroid for UTM and the two Stateplane coordinate systems is Clarke 1866, whereas in ArcView it is GRS80 for UTM, and Stateplane NAD83 and Clarke 1866 for Stateplane NAD27.

Solution or Workaround

The Projector dialog box shows the default spheroid for the projection chosen. If this is not correct, change it from Standard to Custom and type in the projection parameters.

For example, for a coverage with the following parameters:

Stateplane California Zone VI (3401) NAD83
Spheroid Clarke1866
Units Feet

You would use the following PROJECT subcommands in ArcInfo to produce a new UTM coverage:

Code:
INPUT
PROJECTION STATEPLANE
ZONE 3401
DATUM NAD83
UNITS FEET
OUTPUT
PROJECTION UTM
ZONE 11
UNITS METERS
PARAMETERS
END

The default input and output spheroids are both Clarke 1866. The default datum on the output UTM coverage is NAD27.

Starting with the same Stateplane coverage in ArcView, use the following parameters for projecting it into UTM:

Code:
INPUT
Category - Stateplane NAD83
Type - Calif. Zone VI
OUTPUT
Category - UTM
Type - Zone 11

The result can be 100 to 300 meters off.

Note:
Even if the output spheroid is set to Clarke 1866, the results will not match ArcInfo. The Projector extension does not support datum transformations. It is necessary to use the Datum Conversion extension or the NADCON extension available from ArcScripts.

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