I work with ASCAT files as well, and I use the command "scat2gridgauss_xy" to plot over all the passes in the end of a day.
Not sure if I'm doing right, but comparing with the shading output it looks similar (also the "min" and "max" values), I attached an example of the shade picture for the "scat2gridgauss_xy" output ("shadeWIND_SPEEDscat2grid.gif") and for " shade WIND_SPEED, lon,lat" ("shadeWIND_SPEED.gif").
Your question about the shade command got me curious, and for sure, I tried to do the same and I still don't understand, if there isn't interpolation, why it plots in areas between the points of LON/LAT ("plotLONLAT.gif") .
Sorry Ansley, would you explain better this "checkerboard" variable? I reproduced it but could not understand...besides, it uses the "shade" command as well (shade checkerboard, lon, lat), equal "shade WIND_SPEED, lon,lat".
By the end, I had a problem when I tried to do the same as Martin, with the command "curv_to_rect_map", Ferret stops; don't show any error and remains in the in blank display.
I first tried axis with 12.5 km ( ASCAT resolution) and after 1°, but ferrets locks anyway...does anyone have a clue way I'm not able to do it?
OBS: I use FERRET v6.401
Linux(g77) 2.6.9-89.ELsmp - 12/09/09
Above these tests commands:
shade WIND_SPEED,LON,LAT; go land_hires
plot/vs lon,lat ; go land_hires
define axis/x=1:267238:1 tripaxis
define axis/x=0:360:0.1126/UNIT=degrees xaxis
define axis/y=-90:90:0.1126/UNIT=degrees yaxis
let uASCATgrau=scat2gridgauss_xy(lon2,lat2,uASCAT,x[gx=xaxis],y[gy=yaxis],0.2252, 0.2252, 2, 0)
let vASCATgrau=scat2gridgauss_xy(lon2,lat2,vASCAT,x[gx=xaxis],y[gy=yaxis],0.2252, 0.2252, 2, 0)
shade/level=(0,20,1) mag; go land_hires
let checkerboard = 0*wind_speed+mod(i+j,2)
shade/pal=greyscale/lev=(0,2,1) checkerboard, lon, lat
let lonin=lon;let latin=lat
Paula Lamosa Nunes
Date: Fri, 18 Feb 2011 11:23:37 -0800
Subject: Re: [ferret_users] plotting and interpolating data given on curvilinear grids
There is a newer interpolation method in the pipeline, but not yet available. The libcf library being developed by Unidata and a group of collaborators will give us faster tools for interpolating between grids. We are paying close attention to this development and will implement it in Ferret as soon as it's ready. When there's a beta version of the interpolation code, and other capabilities available, we will add it as an option for people to experiment with. Here's the link to the information about libcf:
With the existing tools in Ferret, if all your data has the same curvilienar grid and are interpolating to the same rectilinear grid, you can re-use the map function. This speeds up the entire process quite a lot, and it's the reason we have two functions; one to compute the map and the other to apply it.
The SHADE command only fills each grid box with the corresponding color. It's not doing any interpolation. The curvilinear version of the shade command can use curvlinear coordinate variables that define either the edges of the grid cells or their centers. Here it looks like the grid defines the centers - else their size would be one larger than the grid size of the data fields.
yes? use "ascat_20100111_005400_metopa_16755_eps_o_125_1018_ovw.l2.nc"
yes? sh dat
currently SET data sets:
1> ./ascat_20100111_005400_metopa_16755_eps_o_125_1018_ovw.l2.nc (default)
name title I J K L
TIME time 1:82 1:3259 ... ...
LAT latitude 1:82 1:3259 ... ...
LON longitude 1:82 1:3259 ... ...
cross track wind vector cell nu 1:82 1:3259 ... ...
model wind speed at 10 m 1:82 1:3259 ... ...
model wind direction at 10 m 1:82 1:3259 ... ...
ICE_PROB ice probability 1:82 1:3259 ... ...
ICE_AGE ice age (a-parameter) 1:82 1:3259 ... ...
wind vector cell quality 1:82 1:3259 ... ...
wind speed at 10 m 1:82 1:3259 ... ...
WIND_DIR wind direction at 10 m 1:82 1:3259 ... ...
backscatter distance 1:82 1:3259 ... ...
A nice way to visualize a grid is to define a "checkerboard" variable, which alternates 1 and zero over the grid, based on the variable we're looking at.
yes? let checkerboard = 0*wind_speed+mod(i+j,2)
yes? shade/hlim=50e:150e/vlim=-80:0/pal=greyscale/lev=(0,2,1) checkerboard, lon, lat
So I think what looks in your shade.gif image like data smeared across the middle of this swath is really just the way the shape of the cells changes. The question is why the regridded data has a gap in that area. There should be many points within the 1-degree radius that you've chosen, to use in the interpolation. I don't understand that, but will try to look into it.
On 2/18/2011 8:42 AM, Martin Schmidt wrote:
Description: GIF image
Description: GIF image
Description: GIF image