20010220: creating a mosaic in McIDAS (cont.)

>From: address@hidden (Chris Hennon)
>Organization: Ohio State
>Keywords: 200102121741.f1CHf4L28141 McIDAS mosaic IMGREMAP

Chris,

Sorry I couldn't get to this yesterday.

>> The job of compositing in McIDAS is as simple as:
>> 
>> o create an AREA that covers the region of interest
>> o remap one image into the that AREA
>> o remap the other image into the same AREA that the first was remapped
>>   into
>
>I have "mcidas terminology deficiency syndrome" (MTDS) - how do you
>"create an AREA"?

There are a couple of different ways to create an AREA file. Since
you are wanting to do something very similar to what we do to composite
GOES-East and West, I will describe the process that is instantiated
in the GEWCOMP.MCB and GEWCOMP1.MCB example scripts.

>Say my area of interest is 0,100W (lower left corner), 50N,2.5W (upper
>right corner).

There really is a different mind set in McIDAS and GEMPAK.  In GEMPAK
one always refers to a map area in terms of a lower left corner and an
upper right corner.  In McIDAS one always refers to a map area in terms
of the lower right corner and upper left corner.  Pretty weird, isn't
it.  In defence of McIDAS, all I can say is that it was doing this
before GEMPAK :-)

Before I begin, I should ask what this composite image will be used
in/for.  If you intend for the image to be usable in GEMPAK, then we
may want to stay away from using a METEOSAT image as the base for
remapping.  This is because GEMPAK does not support the METEOSAT
navigation (or it didn't the last time I looked).  This is too bad
since METEOSAT images are really nice for using as a remapping base.
The reason for this is that the subsatellite point is a simple
parameter in the navigation block.  Changing it effectively rotates the
image to whatever longitude you set the value to be.  Remapping into
that image is then straightforward.

Let's first start with using a METEOSAT image as a remapping base
('cause this one is easy).

In the Unidata McIDAS distribution is a number of topographic images.
One of these is an image that covers the western hemisphere.  This
image is in AREA9012, and if you setup the ADDE datasets as per
the online installation/configuration instructions, this image
will be accessible to you as TOPO/WHEMI.  If you didn't setup
the TOPO dataset, we can still proceed by setting up the MYDATA
dataset.

<login as whoever you are running McIDAS as>
<start a McIDAS session>

BATCH MYDATA.BAT

This will setup the MYDATA dataset.  To see the elements of this
dataset, run:

DSSERVE LIST MYDATA

You should get a listing that looks like:

Group/Descriptor         Type  Format & Range     RT Comment
------------------------ ----- ------------------ -- --------------------
MYDATA/GRIDS             GRID  GRID 1-9999           All gridded data in GRID fo
                                                     rmat
MYDATA/IMAGES            IMAGE AREA 1-9999           All images in AREA format
MYDATA/PTSRCS            POINT MD   1-9999           All point source data files
                                                      in MD file format
MYDATA/TOPO              IMAGE AREA 9000-9019        All topographic images in A
                                                     REA format
DSSERVE: done

After this, you should be able to load the WHEMI image in two different
ways:

SF 1

IMGDISP MYDATA/TOPO.13 EU=TOPO

- or -

IMGDISP MYDATA/IMAGES.9012 EU=TOPO

As you can see, the subsatellite point for this image lies at 0,100W:

IMGLIST MYDATA/TOPO.13 FORM=EXP
Image file directory listing for:MYDATA/TOPO
 Pos Satellite/         Date       Time      Center      Res (km)   Image_Size
     sensor                                 Lat  Lon    Lat   Lon
 --- -------------  ------------  --------  ---- ----  ----- ----- ------------
  13  TOPOGRAPHY     1 JAN 96001  00:00:00     0  100
    Band: 1  No Information Available                    9.0   9.0  1232 x 1252
     proj:    0 created: 1996001      0  memo: --- 1-BYTE TOPOGRAPHY FILE ---
     type:PRD      cal type:BRIT
     offsets:  data=    1280 navigation=  256 calibration=  768 auxillary=    0
     doc length:   0   cal length:   0   lev length:   0 PREFIX=   0
     valcod:          0 zcor:  1 avg-smp: N
     pdl:  1  0  0  0  1  0  0  0  0  0  0  0  0  0  0  0
           0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
     start yyddd: 1996019  start time:160000  start scan: 2500
     lcor:   51  ecor:     1  bytes per pixel: 1  ss: 11
     Image Center Point Res (derived)  Lat:   9.04 (km)  Lon:   8.98 (km)

IMGLIST: done

Now, let's make a copy of this image.  This copy will be the AREA that
we will use to remap into:

IMGCOPY MYDATA/TOPO.13 MYDATA/IMAGES.1234 SIZE=ALL

I chose the positon '1234' since the file it represents, AREA1234, is
not one typically used by realtime data ingestion at Unidata sites.
If you have an image stored in AREA1234 that you do not want to mess
with, chose a different position number.

For now, I will continue using positon 1234 as an example.

Now, comes the part where one has to know something about the navigation
block of McIDAS AREA files.  This information is available online
in the McIDAS Programmers Reference Manual:

http://www.ssec.wisc.edu/mug/prog_man/prog_man.html

Select Version 7.6 (it was not updated for McIDAS-X Version 7.7),
and then go to Chapter 7 - Format of the Data Files.  Click on
AREAnnnn    Area (image) files, and you will get to the section
that describes the format of the AREA file.  If you read through
the description of the AREA file, you will eventually get to
the 'Satellite-specific characteristics' page.  When there, click
on the 'Meteosat PDUS' link. In the link page, you will see a
section called 'Meteosat PDUS navigation block'  This defines
the meaning of the words in the navigation block.  The numbering
of the words is 1-256, but they start in the AREA file at word
64 (0 based).  The documentation tells us that the 'center longitude
of rectification (west positive)' is listed in ddmmss (degrees, minutes,
and seconds).

You can list out the contents of the Meteosat navigation block for the
image copy you just made using the McIDAS LWU application:

LWU LIST AREA1234 64
      64. 1297301844       96016 HEX: 4D534154    17710 ASCII: MSAT   w
      66.      93356           0 HEX:    16CAC        0 ASCII:   l
      68.          0        1250 HEX:        0      4E2 ASCII:
      70.    1000000           0 HEX:    F4240        0 ASCII:   B@
      72.          0       96016 HEX:        0    17710 ASCII:        w
      74.          0           0 HEX:        0        0 ASCII:
      76.          0           0 HEX:        0        0 ASCII:
      78.          0           0 HEX:        0        0 ASCII:
      80.          0           0 HEX:        0        0 ASCII:
      82.          0           0 HEX:        0        0 ASCII:
      84.          0           0 HEX:        0        0 ASCII:
      86.          0           0 HEX:        0        0 ASCII:
      88.          0           0 HEX:        0        0 ASCII:
      90.          0           0 HEX:        0        0 ASCII:
      92.          0           0 HEX:        0        0 ASCII:
      94.          0           0 HEX:        0        0 ASCII:
      96.          0           0 HEX:        0        0 ASCII:
      98.          0           0 HEX:        0        0 ASCII:
     100.          0           0 HEX:        0        0 ASCII:
     102.          0           0 HEX:        0        0 ASCII:
 --END OF LISTING

Word 70 in this list is the subsatellite longitude * 10000 (1000000).

Since you are interested in longitudes that range from 2.5W to 100W,
we should change the subsatellite point to 51.25 W.  (NOTE that
longitudes in McIDAS are specified as West positive (go figure)).

51.25 degrees is 51 degrees and 15 minutes.

We use LWU again to change the subsatellite longitude

LWU POKE AREA1234 511500 70

Now, the image has effectively been rotated so that the center of the
image is at the center of your area of interest.

Next display the image:

SF 2
IMGDISP MYDATA/IMAGES.1234 LATLON=30 51:15 EU=TOPO
MAP H

Notice how the map does not conform to the topographic features.  This
is to be expected since we changed the subsatellite point, but we
havn't (yet) done anything with the data.

The next step is remapping the GOES-East and METEOSAT images into this
base.  I don't know what your datasets for these images will be, so
I will show the steps used to remap RTIMAGES/GE-IR into the image and
then display the results:

IMGREMAP RTIMAGES/GE-IR MYDATA/IMAGES.1234 SMOOTH=YES

IMGDISP MYDATA/IMAGES.1234 LATLON=30 51:15 EU=IMAGE REFRESH='EG;MAP H'

So far, we have remapped the GOES-East IR image into the centralized
projection we want.  The next step would be to merge the METEOSAT
image into the same thus creating a composite.  Since I don't have
a METEOSAT image to use, I will simply pretend that there is a
dataset of METEOSAT IR images called MSAT/IR.

IMGREMAP MSAT/IR MYDATA/IMAGES.1234 MERGE=YES SMOOTH=YES

IMGDISP MYDATA/IMAGES.1234 LATLON=30 51:15 EU=IMAGE REFRESH='EG;MAP H'

At this point, you will have a composite of METEOSAT and GOES-East
IR, but you may say that this is not how you wanted to create the
composite (since the values for the meteosat image will overlap/replace
those of the GOES-East image everwhere the METEOSAT image values
exist).

We are not done at this point.  We can do some other steps so that
the compositing will be done along a particular longitude so that
every pixel to the west will be from GOES-East, and every pixel
to the East will be from METEOSAT.  Before we get into how to do
this, I think that you should give the above steps a try and see
if you follow what is happening.  As soon as you are past this, we
can work through doing the compositing using a split method.

For an example of composited GOES-East and GOES-West images, take
a look at:

DATALOC ADD RTIMAGES adde.ucar.edu
IMGDISP RTIMAGES/GEW-IR LATLON=30 100 EU=IMAGE REFRESH='EG;MAP H'

The compositing for these images is done stepwise.  First the
GEOS-West image is added and when the new GOES-East image is
received it is added.  If your display only contains the west
image, then do:

IMGDISP RTIMAGES/GEW-IR.-1 LATLON=30 100 EU=IMAGE REFRESH='EG;MAP H'

to display the previously done composite.

Let me know if you have any difficulties in the example above.  As
soon as you are comfortable with what is going on, we can proceed
to more exotic ways of combining the images.

Tom