mapping data longitude to display longitude

• To: visad-list@xxxxxxxxxxxxx
• Subject: mapping data longitude to display longitude
• From: Steve Emmerson <steve@xxxxxxxxxxxxxxxx>
• Date: Thu, 30 Apr 1998 14:38:58 -0600

Hi,

It appears that one needs to "double up" the beginning and ending
longitude values when displaying a 2-D lat/lon grid.  For example, say
we have a complete 2-D regular lat/long grid of data values on 10 degree
centers.  Then, in order to display it via the following code (for
example):

    display.addMap(new ScalarMap((RealType)domainType.getComponent(0),
        Display.Longitude));
    display.addMap(new ScalarMap((RealType)domainType.getComponent(1),
        Display.Latitude));

the grid must have the following latitude locations:

    -90, -80, -70, -60, -50, -40, -30, -20, -10, 0, 10, 20, 30, 40, 50,
    60, 70, 80, 90

and the following longitude locations:

    0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150,
    160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280,
    290, 300, 310, 320, 330, 340, 350, 360

Note that the values at 0 degrees longitude must be replicated at 360
degrees longitude.  If this is not done, then the field is displayed
with a 0th-order discontinuity at 0 degrees longitude.

Is this true?  And, if so, why and is there a workaround?

--Steve