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NOTICE: This version of the NSF Unidata web site (archive.unidata.ucar.edu) is no longer being updated.
Current content can be found at unidata.ucar.edu.
To learn about what's going on, see About the Archive Site.
Hi Caitlin -- If your surface temperature values are on grids, then you can use the "simple difference" to subtract the two. First, use the Choosers to select the data sources (grid and image), then in the Field Selector, choose "Formula" and drill down in Misc to the difference formula. When you pick that, select an output display (Color shaded plan view), then when you click "display", the IDV will prompt you to identify the two parameters to subtract. (NOTE: if your gridded data is really 3D, then you will need to use the Formula "slice at leve" or "2D slice" when naming the gridded data; the IDV will then ask you to select the grid -- the reason is that the image is 2D and the grid must be 2D as well......) The domain of the first data source will define the domain of the result -- the code will resample the second data source to the domain of the first one and then do the subtraction. If you select the image as the first data source, then the grid (2nd data source) will be sampled onto the image domain -- this might take a while to accomplish.... If you want to find out only where the difference is < 4K, you can use the built-in mask() function to create your own formula. Something like this: mask( (a - b) , "<", 4.0) When you display this, you will be prompted for "a" and "b". Again, just select the two data sources. The display will then contain only 0s and 1s -- and you'll need to create a color table range appropriately. Hope that gets you started.....be sure to check the Users Guide on formulas for more details, if you haven't had a chance already... tom On Wed, Mar 25, 2009 at 4:56 PM, Caitlin Hart <chart2@xxxxxxxxxxxxx> wrote: > Hello, > I am an undergraduate and very new to IDV. > > Is it possible to create composite images out of McIDAS AREA files and > surface plots (GEMPAK or netCDF files)? > > specifically, I am trying to evaluate a fog product and one of the criteria > is that surface temperature - longwave (ch4 on GOES) brightness temperature < > 4K. > > I have AREA files of satellite data and GEMPAK/netCDF files of surface > temperature, but I don't know what to tell IDV in a formula to get a > composite of the two. > > Thank you, > Caitlin Hart > SUNY Brockport Meteorology > > _______________________________________________ > idvusers mailing list > idvusers@xxxxxxxxxxxxxxxx > For list information, to unsubscribe, visit: > http://www.unidata.ucar.edu/mailing_lists/ > -- Tom Whittaker University of Wisconsin-Madison Space Science & Engineering Center (SSEC) Cooperative Institute for Meteorological Satellite Studies (CIMSS) 1225 W. Dayton Street Madison, WI 53706 USA ph: +1 608 262 2759
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