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From: Jeff Whitaker <jswhit@fa...>  20051103 02:25:48

Brian Donovan wrote: > basemap folks, > > I'm trying to understand how the transform_scalar function works. > What are the units of the native projection grid and how are they > determined? I'm trying to scale a scalar data field and overlay it on > the map. Does the location of the origin matter when I do this? To be > clear here's what I'm trying to do. > > 1) I have a Numeric array with a scalar field > 2) I want to overlay this onto a map projection > 3) The data is slightly larger than the map area (in terms of latitude > and longitude) > 4) From the examples it seams like transform_scalar and then imshow > can be used to show the data > 5) I can't seem to use transform_scalar properly > > Thanks is advance, > > Brian Brian: I'm going to assume your data (latlondata) is on a latitude/longitude grid with latitudes lats and longitude lons, and you have created a Basemap instance for your projection regrion (m). Then, to create a nx by ny grid to overlay on the map, all you need is xydata = m.transform_scalar(latlondata,lons,lats,nx,ny) you can then overlay xydata on the map with im = x.imshow(xydata, cm.jet) You only need to do this to plot the data with imshow  with pcolor or contourf you can plot the data on the original lat/lon grid using x,y = m(lons,lons) cs = m.contourf(x,y,latlondata,20,cmap=cm.jet) or im = m.pcolor(x,y,latlondata,shading='flat',cmap=cm.jet) HTH, Jeff  Jeffrey S. Whitaker Phone : (303)4976313 Meteorologist FAX : (303)4976449 NOAA/OAR/CDC R/CDC1 Email : Jeffrey.S.Whitaker@... 325 Broadway Office : Skaggs Research Cntr 1D124 Boulder, CO, USA 803033328 Web : http://tinyurl.com/5telg 
From: Jeff Whitaker <jswhit@fa...>  20051103 02:33:34

Jeff Whitaker wrote: > Brian Donovan wrote: >> basemap folks, >> >> I'm trying to understand how the transform_scalar function works. >> What are the units of the native projection grid and how are they >> determined? I'm trying to scale a scalar data field and overlay it on >> the map. Does the location of the origin matter when I do this? To be >> clear here's what I'm trying to do. >> >> 1) I have a Numeric array with a scalar field >> 2) I want to overlay this onto a map projection >> 3) The data is slightly larger than the map area (in terms of >> latitude and longitude) >> 4) From the examples it seams like transform_scalar and then imshow >> can be used to show the data >> 5) I can't seem to use transform_scalar properly >> >> Thanks is advance, >> >> Brian > Brian: I'm going to assume your data (latlondata) is on a > latitude/longitude grid with latitudes lats and longitude lons, and > you have created a Basemap instance for your projection regrion (m). > Then, to create a nx by ny grid to overlay on the map, all you need is > > xydata = m.transform_scalar(latlondata,lons,lats,nx,ny) > > you can then overlay xydata on the map with > > im = x.imshow(xydata, cm.jet) > > You only need to do this to plot the data with imshow  with pcolor or > contourf you can plot the data on the original lat/lon grid using > > x,y = m(lons,lons) > > cs = m.contourf(x,y,latlondata,20,cmap=cm.jet) > > or > > im = m.pcolor(x,y,latlondata,shading='flat',cmap=cm.jet) > > HTH, > > Jeff > > Brian: One correction  lons and lats are 1d arrays describing the lat/lon grid, so instead of x,y = m(lons,lats) you'll need lons, lats = pylab.meshgrid(lons, lats) x, y = m(lons, lats) Jeff  Jeffrey S. Whitaker Phone : (303)4976313 Meteorologist FAX : (303)4976449 NOAA/OAR/CDC R/CDC1 Email : Jeffrey.S.Whitaker@... 325 Broadway Office : Skaggs Research Cntr 1D124 Boulder, CO, USA 803033328 Web : http://tinyurl.com/5telg 
From: Brian Donovan <donovan@mi...>  20051103 17:06:54

Dr. Whitaker, Thank you for helping me with this. My point of confusion is what should nx and ny contain when they are sent into the transform_scalar function: >> xydata = m.transform_scalar(latlondata,lons,lats,nx,ny) Thanks, Brian On Nov 2, 2005, at 9:32 PM, Jeff Whitaker wrote: > Jeff Whitaker wrote: >> Brian Donovan wrote: >>> basemap folks, >>> >>> I'm trying to understand how the transform_scalar function >>> works. What are the units of the native projection grid and how >>> are they determined? I'm trying to scale a scalar data field and >>> overlay it on the map. Does the location of the origin matter >>> when I do this? To be clear here's what I'm trying to do. >>> >>> 1) I have a Numeric array with a scalar field >>> 2) I want to overlay this onto a map projection >>> 3) The data is slightly larger than the map area (in terms of >>> latitude and longitude) >>> 4) From the examples it seams like transform_scalar and then >>> imshow can be used to show the data >>> 5) I can't seem to use transform_scalar properly >>> >>> Thanks is advance, >>> >>> Brian >> Brian: I'm going to assume your data (latlondata) is on a >> latitude/longitude grid with latitudes lats and longitude lons, >> and you have created a Basemap instance for your projection >> regrion (m). Then, to create a nx by ny grid to overlay on the >> map, all you need is >> >> xydata = m.transform_scalar(latlondata,lons,lats,nx,ny) >> >> you can then overlay xydata on the map with >> >> im = x.imshow(xydata, cm.jet) >> >> You only need to do this to plot the data with imshow  with >> pcolor or contourf you can plot the data on the original lat/lon >> grid using >> >> x,y = m(lons,lons) >> >> cs = m.contourf(x,y,latlondata,20,cmap=cm.jet) >> >> or >> >> im = m.pcolor(x,y,latlondata,shading='flat',cmap=cm.jet) >> >> HTH, >> >> Jeff >> >> > Brian: > > One correction  > > lons and lats are 1d arrays describing the lat/lon grid, so > instead of > > x,y = m(lons,lats) > > you'll need > > lons, lats = pylab.meshgrid(lons, lats) > x, y = m(lons, lats) > > Jeff > >  > Jeffrey S. Whitaker Phone : (303)4976313 > Meteorologist FAX : (303)4976449 > NOAA/OAR/CDC R/CDC1 Email : Jeffrey.S.Whitaker@... > 325 Broadway Office : Skaggs Research Cntr 1D124 > Boulder, CO, USA 803033328 Web : http://tinyurl.com/5telg 
From: Jeff Whitaker <jswhit@fa...>  20051103 17:50:18

Brian Donovan wrote: > Dr. Whitaker, > > Thank you for helping me with this. My point of confusion is what > should nx and ny contain when they are sent into the transform_scalar > function: > > Brian: nx and ny define the resolution of the transformed grid  you should choose them so that the grid spacing on the transformed grid is at least as fine as the original lat/lon grid. Jeff  Jeffrey S. Whitaker Phone : (303)4976313 Meteorologist FAX : (303)4976449 NOAA/OAR/CDC R/CDC1 Email : Jeffrey.S.Whitaker@... 325 Broadway Office : Skaggs Research Cntr 1D124 Boulder, CO, USA 803033328 Web : http://tinyurl.com/5telg 
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