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Re: Projected Data in LAS/Ferret?


The problem is with the LiveMap applet inside of LAS.  There is not any
way currently to tell it that a map is not lon-lat with units in
degrees.  In LAS 5.2 you can associate different maps with individual
datasets or variables but the lon-lat restriction remains.

The only way I've worked around this with "curvilinear" datasets is to
create a new image for the  map and specify the axes in terms of indices
rather than units.  For example I have one dataset where I define axes
like this:

 <Galveston_I type="x">
  <arange start="1" step="1" size="181"/>
 <Galveston_J type="y">
  <arange start="1" step="1" size="101"/>

The applet shows the map but the textfields incorrectly show N and E as
if the units were degrees.  Further hacking was required to get around
the default assumptions when the region is set.

Again using configurability in LAS v5.2 I created a new method (perl
subroutine) to be associated with XY plots for this variable.  Inside of
custom.pl I copied some code from Ferret.pl to create the visualization
but I set the region using I and J instead of X and Y so that Ferret
would interpret these as index space.

The bottom line is that we don't support non-rectilinear, gridded data
but that a determined individual can hack a work-around.

-- Jon

Mark A Ohrenschall wrote:
> Hello,
> I have US Albers equal area grids which I'm attempting to put into
> netCDF and display with LAS/Ferret. I'm able to successfully view a
> test grid with ncBrowse, but no dice with LAS -- in fact, no
> ferret.jnl file or log/GenericLAS_debug.txt files are created
> (modified) when I make the attempt. I've only done unprojected grids
> (degrees_north, degrees_east) before, and I'm not sure how (or if)
> LAS/Ferret handles projected grids.
> Here are how the axes are defined in the LAS configuration fiel:
> <ec_lon type="x" units="meters_east">
>         <arange start="-2405000.0000000" step="10000" size="470"/>
> </ec_lon>
> <ec_lat type="y" units="meters_north">
>         <arange start="255000.0000000" step="10000" size="295"/>
> </ec_lat>
> The netCDF file is only about 550 Kb, and you can get it at
> http://panther.ngdc.noaa.gov/dods/ec.nc -- DODS URL is, e.g.,
> http://panther.ngdc.noaa.gov/cgi-bin/dods/nph-dods/dods/ec.nc.dds --
> in case you want to look at it.
> Thanks in advance,
> Mark Ohrenschall

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