20020227: 20020213: 20020212: reading/writing McIDAS area files for use in GEMPAK

David,

There is a USGS web page poster (which is an overview of
a much larger book on projections that we have):

http://mac.usgs.gov/mac/isb/pubs/MapProjections/projections.html

The suggestion about improving the projection information for users
is good one. 

Thanks for posting the areas.

Steve Chiswell
Unidata User Support



>From: David Ovens <address@hidden>
>Organization: UCAR/Unidata
>Keywords: 200202271852.g1RIqnx15547

>Steve,
>
>First of all, you're a genius!  That orthographic projection is
>terrific!  Thanks for the advice on the labelling bug for longitudes
>being 180 degrees off of the central longitude, too.
>
>Second, is there a reference that I should know about that would have
>clued me in to this projection?  I know next to nothing about
>cylindrical, azimuthal, and conic projections of the earth, and I am
>sure I am not alone.  The PROJ help is informative but assumes one
>knows what these three projections are.  I am thinking about a web
>page that would provide rudimentary information on these projections
>and would show a couple example images of each of the possible
>projections obtainable in GEMPAK along with their GAREA, PROJ, and
>LATLON values for gpmap.  This would help the projection-ignorant such
>as myself find what we're looking for.  The URL could then be added to
>the PROJ help.
>
>Third, I put AREA7799.avn[123].Z into
>http://www.atmos.washington.edu/~ovens/testimages/ for you.
>
>Thank you very much for your help.
>
>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:
>> 
>> 
>> 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 Northwe
> st
>> >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+a
> ll
>> >> >).  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 Nort
> hwe
>> > st
>> >> >Research Meteorologist
>> >> >Dept of Atmospheric Sciences, Box 351640
>> >> >University of Washington 
>> >> >Seattle, WA  98195
>> >> 
>> >> Tom Yoksas
>> >> *************************************************************************
> ***
>> >> Unidata User Support                                    UCAR Unidata Prog
> ram
>> >> (303)497-8644                                                  P.O. Box 3
> 000
>> >> address@hidden                                   Boulder, CO 80
> 307
>> >> -------------------------------------------------------------------------
> ---
>> >> 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
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>> >Organization: UCAR/Unidata
>> >Keywords: 200202122221.g1CMLlx08683
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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)
>> >In-Reply-To: <address@hidden> from "Unidata Sup
> por
>> > t" at Feb 12, 2002 01:59:24 PM
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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 tryin
> g 
>> >> 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 Prog
> ram
>> >> (303)497-8644                                                  P.O. Box 3
> 000
>> >> address@hidden                                   Boulder, CO 80
> 307
>> >> -------------------------------------------------------------------------
> ---
>> >> Unidata WWW Service                        http://www.unidata.ucar.edu/  
>    
>> >> *************************************************************************
> ***
>> >> 
>> >
>> >
>> >-- 
>> >
>> >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
>> >
>> 
>> ****************************************************************************
>> 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/     
>> ****************************************************************************
>> 
>
>