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20020213: 20020212: reading/writing McIDAS area files for use in GEMPAK

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/     
>> ****************************************************************************
>> 
>
>
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>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)
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>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
>