I have implemented a Gantt chart to display the utilisation of resources which are in fact locations, so room1, room2 etc.  I do however want the use of the rooms to be displayed on a single line and not multiple rows for each room.  As such I have created a data source with 5 columns:- series, task, starttime, endtime and owner as in

"room1", "task", 2019-02-06 10:00,  2019-02-06 11:00, "Accounts Meeting"

"room1", "task", 2019-02-06 11:00,  2019-02-06 12:00, "Sales Meeting"

"room1", "task", 2019-02-06 12:20,  2019-02-06 13:00, "Lunch"

"Boardroom", "task", 2019-02-06 09:50,  2019-02-06 12:00, "Board Meeting"

"Boardroom", "task", 2019-02-06 14:00,  2019-02-06 15:00, "Staff Appraisals"

...and so on.  I have set 'task' to be the same for all rows in the data as otherwise each task is listed on a separate line which is not what I want from a Gantt chart.  When displayed I want one row for 'room1' with all uses of room1 along the row and a second row for 'Boardroom' with all of it's uses.  The above data achieves this but probably is not how the control was designed as tool tips do not work correctly.

I therefore created a custom tooltip handler as per another article but i am having issues getting the tooltips to display the correct text which I want to be 'start time - end time (owner)'  I have used the following code to obtain what I thought was the data item for the task for which the tool tip is to be displayed

Dim colIdx As Integer = context("DATA_COLUMN")
Dim rowData = _data.Rows(colIdx).ItemArray

but this returns the same row of data for all of the tasks on the same row - i.e. all room 1 tasks return the same data row and as such the tool tip is always the same. 

Is there an alternate way to display the above data in the way I need it to be or a way of getting the 'correct' data row for the item tooltip?  Seems that this must be a common requirement as many Gantt charts I have seen show usage of a resource along the timeline...