INPUT PROJECTION GEOGRAPHIC UNITS DD PARAMETERS OUTPUT PROJECTION UTM UNITS METERS ZONE 12 PARAMETERS ENDBut the resulting projection is not the same as that used by ArcView. It is actually equivalent to NAD27, whereas ArcView's UTM settings use NAD83. Not even the assumptions regarding lat/long are the same. The following parameters are the equivalent of ArcView's projection from DD to UTM Zone 12:
INPUT PROJECTION GEOGRAPHIC UNITS DD DATUM WGS84 THREE PARAMETERS OUTPUT PROJECTION UTM DATUM NAR_C THREE UNITS METERS ZONE 12 PARAMETERS ENDBecause the GRS80 spheroid is practically identical to WGS84 in the continental U.S., the following parameters will lead to the same values:
INPUT PROJECTION GEOGRAPHIC UNITS DD DATUM NAD83 NADCON PARAMETERS OUTPUT PROJECTION UTM DATUM NAD83 NADCON UNITS METERS ZONE 12 PARAMETERS ENDThus, should you wish to convert NAD27 UTM Zone 12 data to DD for use in ArcView, you may use the following parameters:
INPUT PROJECTION UTM DATUM NAD27 NADCON UNITS METERS ZONE 12 PARAMETERS OUTPUT PROJECTION GEOGRAPHIC UNITS DD DATUM NAD83 NADCON PARAMETERS ENDNote also that ArcView cannot "unproject" according to Clarke1866; therefore, you will need to use the above parameters (in reverse) to bring DD data created for ArcView into your PC A/I project.
A good rule of thumb regarding the appropriate parameters for abstract data (e.g. lat/long lines) is to ask yourself how you want the features to "appear" relative to a particular projection. For example, USGS 7.5' quads (except the newest ones) use NAD27 lat/long frames; if you were to use the above parameters to project a lat/long frame, it would match the NAD83 ticks.