Orthophotographs shifting by 65m

[MattMcCrisken]

Hi there, excuse the lack of specific terms, I'm new to ESRI and ARCPad

I have a Magellan Mobile Mapper CX running ARCPad 7.1.
I also have ARCMap 10 desktop.
Using the ARCPAD toolbar in ARCMap 10 I have exported point, line and polygon layers, plus a basemap and an orthophotograph to the SD card of the Magellan.
The image and layers are georeferenced to Irish Grid TM65 on the Desk top and I have set the datum on the Magellan to TM65.
However, when I used the GPS funstion in ARCPad to plot 4 points around a car park, which was shown on the ortho, it was plotted about 65m east of where it was on the photo.
Assuming that the GPS was accurate, the photo is shifted left on the screen by 65m. Sizes and scales are fine, just the location.

Any ideas or help much appreciated.

Matt

[RolfBroch]

Most GPS's use WGS84 as their datum and this is also the default setting in ArcPad, that is, ArcPad expects that the incoming lat lon coordinates are in WGS84.

When you say you set the Magellan to TM65, do you mean that you ask the Magellan to show coordinates on the screen in TM65 datum or is the output from the GPS to ArcPad set to TM65? If the latter, you also need to change the GPS datum for ArcPad to TM65.

I have not worked with TM65 or Magellan before so this may or may not be the case in your instance.

Rolf