Canon GP-E2 Instruction Manual page 13

Places with Poor GPS Coverage
Location information may not be recorded, or inaccurate information may be
recorded where GPS signal coverage is poor, such as in the following
places.
Indoors, underground, near buildings or in valleys, in tunnels or forests
Near high-voltage power lines or mobile phones operating on the
1.5 GHz band
When the receiver is inside a bag or suitcase
When traveling through different environments
Even in other places, GPS satellite movement may interfere with
geotagging and cause missing or inaccurate location information. The
information may also indicate hat the camera has been used in a
different location, even if you are shooting at the same place.
Appended Information
When the receiver and the camera are connected with a cable, shots
taken immediately after turning on the camera's power switch (or
resuming use after auto power off) may not be geotagged. Similarly,
directions may not be recorded correctly. To avoid this, either attach the
receiver to the hot shoe (except for the EOS 7D) or wait a moment
before shooting. When the receiver is attached to the hot shoe, do not
connect the camera and receiver with a cable.
If mirror lockup is performed when the receiver is attached to he hot
shoe, location information where the mirror was locked will be attached
to the images. If mirror lockup is performed when the receiver is
connected to the camera with a cable, shooting location will be attached
to he images as location informa ion. For convenience, he receiver can
be left attached to the hot shoe.
Acquiring GPS Signals
13