This archive contains answers to questions sent to Unidata support through mid-2025. Note that the archive is no longer being updated. We provide the archive for reference; many of the answers presented here remain technically correct, even if somewhat outdated. For the most up-to-date information on the use of NSF Unidata software and data services, please consult the Software Documentation first.
David, I looked at your gif inages in the testimages directory below. Can you also put a sample of your AREA file with the poked values in that directory so that I can look at the map drawing? I did some playing around with the existing projections that already exist in GEMPAK. I believe the Orthographic projection accomplishes what you originally described. For example, I created a globe-like plot using the following in GPMAP: GAREA = 0;-135;0;-135 PROJ = ort/35;-135;0 LATLON = 6/1/1/1;1/20;20/10;-135 The latlon drawing is a little sensitive (eg buggy) when the longitude drawn on the back side of the earth is 180 degrees oposite the central longitude - so I picked the longitude increment of 20 (instead of 15) to avoid that problem. Steve Chiswell Unidata User Support >From: David Ovens <address@hidden> >Organization: UCAR/Unidata >Keywords: 200202130953.g1D9rkx03539 >Steve and Tom, > >If you look in http://www.atmos.washington.edu/~ovens/testimages/ >you will find 3 GIF images and 3 commented *lwu_pokes files that show >how the bogus McIDAS AREA file used in the corresponding plot was >generated. Turns out that once I found the right words to POKE, this >was possible and both McIDAS-X and GEMPAK can handle it (for the most >part). One thing I am wondering if you could still help on is the >apparent bug in the mapping. Look for Greenland in the various plots >and you'll see that only avn3_2002021300_000.gif has its complete >outline. Similar disappearances of the lat/lon lines also occur near >the pole. > >I realize that what I've done to generate the AREA file is pretty >klugey, but I still wonder if I can get trick GEMPAK into creating >avn1_2002021300_000.gif with a full map and lat/lon lines. If I add >more bogus data to the file to correspond to the POKEd words (5, 6, 8, >and 9), would this make the maps and lat/lon labels around the pole >reappear? > >David >-- > >David Ovens e-mail: address@hidden >(206) 685-8108 plan: Real-time MM5 forecasting for Pacific Northwest >Research Meteorologist >Dept of Atmospheric Sciences, Box 351640 >University of Washington >Seattle, WA 98195 > > >Unidata Support wrote: >> >> >From: David Ovens <address@hidden> >> >Organization: University of Washington >> >Keywords: 200202121913.g1CJDNx21764 McIDAS AREA >> >> David, >> >> Chiz already responded to you on this from a GEMPAK perspective, but >> I figured I would throw in my 2 cents worth on the McIDAS side. >> >> >I am hoping to create a bogus McIdas area file -- basically a GOES-10 >> >image rotated up so Seattle is about at the center of the image -- so >> >that I can get a different satellite projection in GEMPAK (if you want >> >an example of what my output would look like, see >> > http://www.atmos.washington.edu/~ovens/loops/wxloop.cgi?joes_okc_h500+all >> >). Anyhow, I think that all I need to do is figure out how to read an >> >existing McIdas file (GOES-10) and write it back out changing only the >> >4th word in the navigation section from "102042" to "474500" or >> >something like that. Is there FORTRAN (preferably), C, or PERL code >> >out there that could help me with this? >> >> This can easily be done in McIDAS. You can use the LWU command to list >> out and change values in any file. So, for instance, let's suppose >> that the image you want to play around with is in file AREA1234. >> Use LWU from a McIDAS session to list out the first 64 words of the >> file: >> >> LWU LIST AREA1234 0 63 >> >> Now, suppose you wanted to change the value of word 123 to 474500: >> >> LWU POKE AREA1234 474500 123 >> >> Remember that the index into the file that LWU will use is zero based. >> >> As a side comment, the GVAR navigation model is so complex that I don't >> think that changing the value of one word in the NAV block will do the >> rotation that you want. But hey, I have never tried this so go for >> it! >> >> After changing a NAV value, you will need to redisplay the image >> and then draw a map on it to see the effect: >> >> IMGDISP MYDATA/IMAGES.1234 REFRESH='EG;MAP' >> >> If this fails, it means that you can not simply change one NAV parameter >> in the GVAR navigation and be successful. >> >> One navigation that does lend itself to simple rotations in McIDAS is >> that for METEOSAT. The subsatellite longitude is called out explicitly >> in METEOSAT imagery. Changing it effectively rotates the image to >> the new longitude. What is not called out, however, is the subsatellite >> latitude as that is assumed to be the equator. The only problem for >> you using a METEOSAT image is that GEMPAK does not support METEOSAT >> navigation. >> >> >By the way, I have looked at maknav and imgremap in McIdas-X and I >> >understand the LAMB, MERC, PS, RADR, RECT, and MOLL projections, it's >> >possible that SIN, TANC, or NOAA does what I want, but I don't >> >understand those. Basically, I didn't see how I could do a new >> >satellite projection if I did not already have a file with the >> >projection that I want to create. >> >> IMGREMAP can be used to write image data into a new AREA file >> specifying the projection that you want. The projections >> supported by IMGERMAP for new output files are: >> >> =LAMB slat1 slat2 slon | Lambert Conformal, standard latitude >> and standard longitude (slat1 def=30, >> slat2 def=50, slon def=center longitude) >> =MERC slat | Mercator projection and standard latitude (slat def=0) >> =MOLL slon | Mollweide projection and standard longitude (slon def=0) >> =PS slat slon | Polar Stereographic projection, standard latitude >> and standard longitude >> (slat def=60, slon def=center longitude) >> =RADAR rot | Radar projection and rotation angle (rot def=0) >> =RECT | Rectilinear projection >> =SIN | Sinusoidal Equal Area projection >> =TANC slat slon | Tangent Cone projection, standard latitude and >> >> If you want the navigation of the resultant image to be that for GVAR, >> then your only option is to remap into an existing image. >> >> I am curious to hear the results of your changing NAV parameters in >> a GVAR image! >> >> >Thanks for any help or suggestions. >> > >> >David >> >David Ovens e-mail: address@hidden >> >(206) 685-8108 plan: Real-time MM5 forecasting for Pacific Northwe > st >> >Research Meteorologist >> >Dept of Atmospheric Sciences, Box 351640 >> >University of Washington >> >Seattle, WA 98195 >> >> Tom Yoksas >> **************************************************************************** >> Unidata User Support UCAR Unidata Program >> (303)497-8644 P.O. Box 3000 >> address@hidden Boulder, CO 80307 >> ---------------------------------------------------------------------------- >> Unidata WWW Service http://www.unidata.ucar.edu/ >> **************************************************************************** >> > > >From address@hidden Tue Feb 12 15:21:48 2002 >Received: from blizzard.atmos.washington.edu (blizzard.atmos.washington.edu [1 > 28.95.175.12]) > by unidata.ucar.edu (UCAR/Unidata) with ESMTP id g1CMLlx08683 > for <address@hidden>; Tue, 12 Feb 2002 15:21:47 -0700 (MST) >Organization: UCAR/Unidata >Keywords: 200202122221.g1CMLlx08683 >Received: (from ovens@localhost) > by blizzard.atmos.washington.edu (8.11.6+Sun/8.11.6) id g1CMLld06158 > for address@hidden; Tue, 12 Feb 2002 14:21:47 -0800 (PST) >From: David Ovens <address@hidden> >Message-Id: <address@hidden> >Subject: Re: 20020212: sat projection in GEMPAK >To: address@hidden >Date: Tue, 12 Feb 2002 14:21:46 -0800 (PST) >In-Reply-To: <address@hidden> from "Unidata Suppor > t" at Feb 12, 2002 01:59:24 PM >X-Mailer: ELM [version 2.5 PL2] >MIME-Version: 1.0 >Content-Type: text/plain; charset=us-ascii >Content-Transfer-Encoding: 7bit > >Steve, > >Thanks for the idea, but the professor for whom I doing this really >wants that circular, satellite view that NCARGraphics is able to >provide. I can still use the NCARGraphics code, but it takes about >5-10 times as long to run and is prone to failing every week or two >(something to do with attempting to do contours at the limb, I >think). If I can get a fake satellite image, then GEMPAK can do it >for me. > >Too bad GEMPAK doesn't have the ability to do SAT projections all by >itself. > >I will come up with a solution and let you and Tom know what it is. > >David > > >Unidata Support wrote: >> >> >From: Unidata User Support <address@hidden> >> >Organization: Unidata Program Center/UCAR >> >Keywords: >> >> >> David, >> >> As I figured, Tom was able to suggest an easy way to create the >> satellite projection for an AREA file. As an asside, if you weren't trying >> to project a satellite image, but rather just wanted to give the >> illusion of the disk then you could use other GEMPAK projections >> such as rotated cylindrical projections (depending on how much you wanted to >> zoom in on Washington). Such as: >> GAREA = -10;-180;20;-30 >> PROJ = ced/45;-120;90 >> >> >> Steve CHiswell >> **************************************************************************** >> Unidata User Support UCAR Unidata Program >> (303)497-8644 P.O. Box 3000 >> address@hidden Boulder, CO 80307 >> ---------------------------------------------------------------------------- >> Unidata WWW Service http://www.unidata.ucar.edu/ >> **************************************************************************** >> > > >-- > >David Ovens e-mail: address@hidden >(206) 685-8108 plan: Real-time MM5 forecasting for Pacific Northwest >Research Meteorologist >Dept of Atmospheric Sciences, Box 351640 >University of Washington >Seattle, WA 98195 >