fixed grid format of ABI/AHI ==> ADDE

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joleenf
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fixed grid format of ABI/AHI ==> ADDE

Post by joleenf »

Hi,

I was wondering how the fixed grid format of AHI and ABI is carried into the NAV block for the ADDE served AREA files? Does the NAV block retain the

    - Scale,
    - offset for x&y,
    - sub-satellite point (dir block does, correct?),
    - eccentricity?

If this information is contained in the NAV block, how does McIDAS-V access this information? I am asking this question so that we might be able to use the fixed grid format to resample the higher resolution grid to 1 km before projecting onto the earth when performing channel combinations.

Thanks,
Joleen
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bobc
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Re: fixed grid format of ABI/AHI ==> ADDE

Post by bobc »

Hi Joleen -

I'll probably have to forward this to a programmer, but I'm looking to get a bit of clarification first. You specifically mentioned AREA files. The only fixed grid format ABI data that I've worked with myself is in the NetCDF format. These files can be loaded through the General>Files/Directories chooser, as well as local servers (if on Linux or OS X), and remote servers. The local and remote servers both use NetCDF-formatted data.

Can you please point me towards some of these AREA files for testing?

Thanks -
Bob Carp
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joleenf
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Re: fixed grid format of ABI/AHI ==> ADDE

Post by joleenf »

Hi Bob,

That is correct, I am just wondering if when the ABI files are converted to AREA, the original projection information gets retained as documentation.

Joleen
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bobc
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Re: fixed grid format of ABI/AHI ==> ADDE

Post by bobc »

Hi Joleen -

It is possible to obtain this navigation block information in McIDAS-V. Here is how you would go about doing this:

  1. Run your loadADDEImage command. In my example, I ran:

    Code: Select all

    data=loadADDEImage(**addeParms)

    * At this point, you can run:

    Code: Select all

    type(data)

    ... and you will see that you are working with a MappedAreaImageFlatField.
    * Looking at the AreaFile class in the javadocs, there is a getNav() method that returns the navigation block of the data. However, you can't pass a MappedAreaImageFlatField through this method.
  2. Run the AreaFile constructor (described in the AreaFile javadoc) on the URL returned from your loadADDEImage function. This URL should print out in the Jython Shell. In my case, I'm defining this as abiArea:

    Code: Select all

    abiArea = AreaFile('url_returned_from_loadADDEImage')

    * At this point, you will see that abiArea is a type AreaFile.
  3. Pass this abiArea object through the getNav() method to return the navigation block:

    Code: Select all

    abiArea.getNav()
You will notice that there are only 7 navigation parameters in the navigation block, and the rest of the block is 0 (zero) filled. This is much different than the navigation block returned from GOES East, which has a lot more values. I passed this around to a few programmers to verify that this makes sense, and here was the response:
Both ABI and AHI need only 7 navigation parameters. These are the basic values listed in Joleens original email. The rest of the navigation block is 0 (zero) filled. The way these vlues are used by the respective navigation transforms is quite different. That is why they do not share a common dlm member.

If you have any questions, please let us know.

Thanks -
Bob
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joleenf
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Re: fixed grid format of ABI/AHI ==> ADDE

Post by joleenf »

Hi Bob,

The first part of the nav array seems to have some of the information that I am looking for, but perhaps not all:
array('i', [1094863182, 15186500, -15186500, -1400, 1400, -895, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0...

I think that indices 1,2 might be the x and y offsets from the DOE-4 files, but I can't find the scale_factor anywhere in the list. It appears that index 5 is the longitude center, but what about the latitude center? Is it really 1?

Thanks,
Joleen
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bobc
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Re: fixed grid format of ABI/AHI ==> ADDE

Post by bobc »

Hi Joleen -

I just wanted to let you know that I forwarded this off to the ABI programmer to let us know what each of the 7 values in the navigation block are. I'll respond back to this forum when I hear back from him.

Thanks -
Bob
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bobc
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Re: fixed grid format of ABI/AHI ==> ADDE

Post by bobc »

Hi Joleen -

From the ABI server programmer:
The definition for the 7 values is documented in the navigation dlm (NVXABIN.DLM)
These are:
C IPARMS: Navigation Block:
C 1: ABIN
C 2: LOFF
C 3: COFF
C 4: LFAC
C 5: CFAC
C 6: Satellite SubPoint Longitude
C 7: Base Resolution

LFAC/CFAC - Line and Column scale factors
LOFF/COFF - Line and column offset

Please let me know if you have any further questions about this.

- Bob
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joleenf
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Re: fixed grid format of ABI/AHI ==> ADDE

Post by joleenf »

A slightly related question that I can't remember if I already asked:

I have loaded part of a GOES-16 CONUS dataset, is there a method to determine the center location of the partial data and convert from fixed grid to lat/lon already built into the McIDAS-V software? This center location determination would occur before displaying the data.

Thanks,
Joleen
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bobc
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Re: fixed grid format of ABI/AHI ==> ADDE

Post by bobc »

Hi Joleen,

I've been looking into extracting the center lat/lon from the data object returned from loadADDEImage. I was hopeful that I could make use of the VisAD AreaFile class, but I'm not finding a way to get at it. The only thing I've found so far is making use of the URL returned from loadADDEImage, where you can parse the string to extract the lat/lon values. This would only work if you specified a center lat/lon in your loadADDEImage call. Here's an example:

Code: Select all

addeParms = dict(
    server = 'easta.ssec.wisc.edu',
    dataset = 'EAST',
    descriptor = 'CONUS',
    band = 10,
    coordinateSystem = LATLON,
    location = (40.8, -98.4),
    place = 'CENTER',
    size = (400, 400),
    mag = (1, 1),
    showUrls = False,
    )
data = loadADDEImage(**addeParms)
url = data['url']

# split the string so only text after LATLON= is included
parse1 = urlLatlon = url.split("LATLON=",1)[1]
# further split the string by including up to the second space,
# to only include the latitude and longitude values
parse2 = " ".join(parse1.split(" ",2)[:2])

print 'The center lat lon is: %s' % parse2

I'll have to check with the programmers about your second question, converting the data from fixed grid to lat/lon. I'm not aware of any way to do this myself. If I discover an alternative way of getting the center lat/lon of the data object returned from loadADDEImage I'll let you know.

Thanks,
Bob
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joleenf
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Re: fixed grid format of ABI/AHI ==> ADDE

Post by joleenf »

Hi Bob,

I should have started a new General Question thread for this. I was asking about getting the actual center from a loadGrid object where a xRange, yRange selection has been implemented to reduce the size of data loaded.

Joleen
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