Geographic Transformations and 'Layer to KML' Tool

Question

I'm attempting to export some shapefile data that is projected in UTM Zone 9 NAD 1927 to kml using the 'Layer to KML' tool. Unfortunately, the geographic transformation that appears to be selected by the tool results in the features being shifted about 120 metres away from their true position (I have a sample of the same data exported using Global Mapper which I know to be accurate for comparison).

I primarily wanted to know how a transformation is selected by the 'Layer to KML' tool. The features are in northern British Columbia and I've attempted to export data that I've pre-projected into WGS84 using the transformations: 
- 1179 (NAD_1927_To_WGS_1984_10 which I understand is suitable for BC and Alberta) and 
- 1176 (NAD_1927_To_WGS_1984_7 which is more appropriate for Alaska).

The resulting kml data from both of these projections are closer, within 20 metres of the true position. However, the data from the Global Mapper export is almost halfway between the resulting data sets when all 3 are loaded into Google Earth.

I need to be able to export directly out of ArcGIS desktop (from NAD27) to kml, so if anybody can offer a solution I'd greatly appreciate it. Cheers!

(I've re-posted this request here because of the recent migration of the support forums)

PrashantMakwana · Answer

What is an appropriate transformation method to transfer from NAD_1927_To_WGS_1984 for Alberta ?

MelitaKennedy · Answer

I don't know what the Layer-to-KML tool is using for a transformation. It is probably whatever transformation is "active" in the dataframe, or any preset transformations in the geoprocessing environment. For Canada, it might be more accurate to use the NTv2-based transformation, NAD_1927_To_WGS_1984_33.

However, if you don't have it, you will need to download the NTv2 file that this transformation requires. You can download the file at http://www.geod.nrcan.gc.ca/tools-outils/ntv2_e.php. You first will need to get a free account for CSRS database. In the NTv2 for Windows software includes the Ntv2_0.gsb file. Once you get that file, place it in your ArcGIS software location, pedata, ntv2, canada folder (you'll need to create the canada folder).

Melita