Re: Gridded2DSet of Lat/Lon

• To: Curtis Rueden <curtis@xxxxxxxxxxxxx>
• Subject: Re: Gridded2DSet of Lat/Lon
• From: Leah Foechterle <leah@xxxxxxxxxxxxxxxxxx>
• Date: Fri, 14 Mar 2003 16:59:29 -0800 (PST)

Ok.  I've figured out my problem.  Some of my longitudes were 
positive values where most of my longitudes were negative values
(I was wrapping around the N. Pacific).  I noticed this when I
tried plotting with an Irregular2DSet.  

So, if I modify my longitude values (lon -= 360 for lon > 0)
my lat/lon points do form a valid grid.

Great!  I can have a relaxing weekend now that I've gotten this
figured out.

:)

Leah


**************************
Leah Foechterle Heiss
Engineer III
Applied Physics Laboratory
University of Washington
Seattle, WA
**************************


On Fri, 14 Mar 2003, Curtis Rueden wrote:

> Hi Leah,
> 
> The algorithm requires that each box of the grid be convex, and
> that the direction of the samples (clockwise vs counterclockwise)
> be consistent.  It checks this by comparing "signatures" between
> grid boxes. The Lambert conformal conic projection should form a
> valid grid, except where the grid converges on a single point at
> the top.
> 
> Because the algorithm will most likely fail if you have colocated
> samples, I recommend spacing the topmost samples of the
> projection a very small distance apart from one another, in such
> a way that the validity of the grid is maintained.
> 
> -Curtis
> 
> At 10:00 AM 3/14/2003, Leah Foechterle wrote:
> >I'm trying to create a Gridded2DSet of Lat and Lon values
> >but the constructor throws an Exception: "samples do not
> >form a valid grid".  I'm using the following constructor...
> >
> >public Gridded2DSet( MathType type, float[][] samples, int lengthX, 
> >int lengthY)
> >
> >My Lat/Lon values are on a Lambert Conformal grid projection, 
> >but I haven't defined the Coordinate System because I didn't
> >think it was necesssary (and it seems complicated -- there are
> >alot of parameters associated with a Lambert Conformal projection).
> >
> >My float[][] samples are loaded from files such that 
> >samples[0][] = latitudes and samples[1][] = longitudes (reversing
> >these doesn't avoid the exception).
> >
> >I've looked at the Gridded2DSet code to try to figure out why my
> >"samples do not form a valid grid" but I don't understand the 
> >algorithm that determines this.
> >
> >Has anyone else had this problem or could someone explain to me
> >the algorithm that says my grid is not be valid?
> >
> >
> >Leah
> 

• References:
  • Re: Gridded2DSet of Lat/Lon
    • From: Curtis Rueden