On Mon, Feb 3, 2014 at 6:09 AM, Timothy Lebo <lebot@xxxxxxx> wrote:
> How can (or should) LiDAR be modeled in NetCDF-4?
>
NetCDF is very flexible -- if you want to know how best
to represent particular data in a standard way, you'll want o use a defined
standard. Most commonly used is the "CF" metadata standard (CF for Climate
Forecast, but is has been expanded and adopted for all sorts of other
things):
http://cf-pcmdi.llnl.gov/
A quick search of the standard name table does not turn up "lidar", but I'd
be really surprised if it hadn't been used for that, so I'd puruse teh
standard and see what matches your data well.
> I’m a NetCDF novice, and it seems to me that the format assumes uniformly
> spaced samples (e.g. [1]).
>
NetCDDF works really well for regular gridded data, but it by no means
is restricted to that. You certainly dont want to arbitrarily shift your
data points to a regular grid.
Below is a table of sample points that I’d like to encode in NetCDF. It
> originates from a USGS LAS file about Disneyland.
>
> lat lon alt intensity
> category(Ground=2;Low-Vegetation=3;Unclassified=1;Water=9)
> 414783.24 3741669.72 40.32 26 9
> 414782.09 3741669.31 40.44 3 9
> 414782.73 3741670.04 40.40 10 9
> 414782.03 3741670.63 40.28 26 9
> 414781.51 3741671.03 40.34 22 9
>
if I"m reading this right, you have a whole bunch of points, each with a
lat-lon, and a couple values and a flag associated with that. If there is
no particular structure to the arrangement of the point, then you want to
keep it as unstructured data:
a bunch of 1-d arrays, length-number-of-points long:
latitude
longitude
alt
intensity
catagory
it's pretty much that simple, but browse through the CF standard to see how
you want to label then and what mets-data to apply so that users will be
most easily able to interpret the data.
I think you want to look at what CF calls "Discrete Sampling Geometries".
If it's unclear what do do a post to the CF list would probably result in
good advice:
http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
> My latest attempt is at [3] and included below, but it isn’t satisfactory
> because I’m forced to round my points to suit a grid.
>
yeah, you really don't want to do that...
-Chris
--
Christopher Barker, Ph.D.
Oceanographer
Emergency Response Division
NOAA/NOS/OR&R (206) 526-6959 voice
7600 Sand Point Way NE (206) 526-6329 fax
Seattle, WA 98115 (206) 526-6317 main reception
Chris.Barker@xxxxxxxx
