Grouping Consecutive Rows In A Table

SQL Server 2008.

From individual event logs I have generated a table where arrivals and departures at a location are registered per device. As there are multiple registration points, there might be multiple consecutive registrations per location.
If this is the case I need to filter those out and have one registration per location and in the result I need to get the earliest arrival and the latest departure of these consecutive rows.

Part of the table:

logIDdeviceIDArrivedDepartedLocationIDGrp1Grp2Grp
3485441082013-02-07 17:51:05.0002013-02-07 17:51:15.0005110
3492041082013-02-07 17:51:15.0002013-02-07 17:51:26.0005220
3500241082013-02-07 17:51:27.0002013-02-07 17:51:37.0003312
3508941082013-02-07 17:51:41.0002013-02-07 17:51:54.0004413

[Code] ....

So as long the field LocationID is the same in the next row, it needs to be grouped.

I have added the rows Grp1, Grp2, Grp in an attempt to get an unique grouping number with the following script in the select statement:

,ROW_NUMBER() OVER(PARTITION BY DeviceID
ORDER BY logID) AS Grp1
,ROW_NUMBER() OVER(PARTITION BY DeviceID, LocationID
ORDER BY logID) AS Grp2
,ROW_NUMBER() OVER(PARTITION BY DeviceID
ORDER BY logID)
-
ROW_NUMBER() OVER(PARTITION BY DeviceID, LocationID
ORDER BY logID) AS Grp

By subtracting Grp2 from Grp1 (Grp = Grp1 - Grp2) I hoped to get an unique group number for each set of equal consecutive locations, however the Grp2 column does not restart from 1 each time the LocationID changes: Grp2 in line 7 should have been 1 again, but it is 2 because this is the second row with LocationID = 3 in the list.