Hello, I will answer two questions you sent to me outside of the list.  First, some general comments about interpolation in Ferret. MODE INTERPOLATE controls whether Ferret interpolates results when getting data out of a grid.  So, for instance, say you have a data on an axis which is every 10 degrees, such as      define axis/x=0:360:10/units=degrees_east and you ask Ferret to list data at x=28E.  With MODE INTERPOLATE turned on, Ferret would do a linear interpolation between the data values at x=20 and x=30 and return that interpolated result.  If MODE INTERPOLATE is off, it would return the data at the nearest location, x=30. Interpolating to a grid can mean a couple of different things.  For your data, which is ungridded data with locations lon, lat and data at lon,lat; we use one of the scat2grid functions, as you show here. If the data is gridded, then interpolating to another grid is referred to in the documentation as "regridding".  Finally if you had gridded data, and wanted data at a set of X,Y locations, that would be "sampling". Now, about scat2gridgauss_xy. The script you sent earlier needs one change.  You had this: yes? use wm_20110101.nc yes? DEFINE AXIS/X=15E:120:10/UNIT=DEGREES xlon yes? DEFINE AXIS/Y=-60S:30N:10/UNIT=DEGREES ylat yes? DEFINE GRID/X=xlon/Y=ylat gsnoopy2d The Y axis definition should not have -60S, but either 60S or -60, without the S. yes? use wm_20110101.nc yes? DEFINE AXIS/X=15E:120:10/UNIT=DEGREES xlon yes? DEFINE AXIS/Y=60S:30N:10/UNIT=DEGREES ylat yes? let swhcorgrid = scat2gridgauss_xy (lat, lon, swhcor, x[gx=xlon], y[gy=ylat], 4,2,4,2) yes? stat swhcorgrid                SCAT2GRIDGAUSS_XY (LAT, LON, SWHCOR, X[GX=XLON], Y[GY=YLAT], 4,2,4,2)              LONGITUDE: 10E to 130E              LATITUDE: 65S to 35N              Z:  N/A              T:  N/A              E:  N/A              F:  N/A              DATA SET: ./wm_20110101.nc    Total # of data points: 120 (12*10*1*1*1*1)  # flagged as bad  data: 40  Minimum value: 0.62119  Maximum value: 5.3594  Mean    value: 2.6417 (unweighted average)  Standard deviation: 1.1658 On 2/4/2014 10:55 PM, Selvam G. wrote: Dear Prof, I tried another command with scat2gridgauss_xy , In this Interpolation data points are drawn. please guide me for Interpolating data points within this region, LON=15:120 and LAT=-60:30.  yes? let swhcorgrid = scat2gridgauss_xy (lat, lon, swhcor, x[gx=xlon], y[gy=ylat], 4,2,4,2) yes? stats swhcorgrid                SCAT2GRIDGAUSS_XY (LAT, LON, SWHCOR, X[GX=XLON], Y[GY=YLAT], 4,2,4,2)              LONGITUDE: 10E to 130E              LATITUDE: 25N to 65N              Z:  N/A              T:  N/A              E:  N/A              F:  N/A              DATA SET: ./wm_20110101.nc    Total # of data points: 48 (12*4*1*1*1*1)  # flagged as bad  data: 17  Minimum value: 0.5978  Maximum value: 4.3431  Mean    value: 1.6993 (unweighted average)  Standard deviation: 1.3002 yes? let xlon = XSEQUENCE(lon) yes? let ylat = YSEQUENCE(lat) yes? let yswhcor = YSEQUENCE(swhcor) yes? let salinite = SCAT2GRIDGAUSS_XY(xlon,ylat,yswhcor,x[gx=xlon],y[gy=ylat],2,2,2,2) yes?  regards, Selvam G. From: "Ansley Manke" To: "Selvam G." Cc: "ferret users" Sent: Tuesday, February 4, 2014 11:18:17 PM Subject: Re: [ferret_users] Spatial Trend Hello, Your data is organized as lists of longitude, latitude, time and measurements. You used a good method, plot/vs/ribbon, to visualize the density and range of the data. yes? go basemap x=15:120 y=-60:30 yes? plot/vs/over/nolab/ribbon/thick/size=0.08/symbol=17/key/LEV= v LON,LAT,SWHCOR To interpolate it to a grid, use one of the SCAT2GRID functions    yes? show function scat2grid*xy Perhaps the scat2gridgauss_xy function. A note on the syntax: in your axis definition, the latitude axis should be one of these: DEFINE AXIS/Y=60S:30N:10/UNIT=DEGREES ylat DEFINE AXIS/Y=-60:30:10/UNIT=DEGREES ylat Not -60S.  -Ansley On 2/3/2014 7:49 PM, Selvam G. wrote: ```Dear Prof, I would like to know the ferret command for linear Interpolation. I am dealing with Ifremer altimeter wave data for Indian Ocean.I plotted the map but when the Interpolation command is given the .des file is not shown as it is Interpolated. I am attaching one of my wave data for your consideration. I request your guidance for this Interpolation. Thanks & regards Selvam G. ----- Original Message ----- From: "Russ Fiedler" To: "ferret users" Sent: Tuesday, February 4, 2014 3:16:38 AM Subject: Re: [ferret_users] Spatial Trend The time units for the trend should correspond to the time axis for your data. If it's days then you will have to multiply by 365 or 365.25 to get the trend in terms of years. Russ On 03/02/14 23:45, iwlod@xxxxxxxxxxxxxxxxxxx wrote: ``` ```I dont think it is that simple - units on slope are way to small can someone else confirm? thanks ``` ```Simply shade slope. Sent from my iPhone ``` ```On Jan 31, 2014, at 4:17 AM, iwlod@xxxxxxxxxxxxxxxxxxx wrote: Collective Ferret Wisdom :-) How do I go from a linear regression line plot (with go regresst) to a SPATIAL (lat x lon) trend map of say, temperature for the past 20 years? Thank you ```