Incorrect translation of SIGMET TAC location into xml <iwxxm:geometry> (degrees, minutes) to (decimal degrees)

[padhrigmccarthy]

Describe the bug Lat/lon points in SIGMET example https://github.com/wmo-im/iwxxm/blob/master/IWXXM/examples/sigmet-multi-location-VA.tac appear to be incorrectly translated to https://github.com/wmo-im/iwxxm/blob/master/IWXXM/examples/sigmet-multi-location-VA.xml.

The units of the TAC location points are in (degrees, minutes): "AND OBS AT 1200Z WI N4200 E02115 ..."

The units of the iwxxm:geometry are in (decimal degrees), but improperly converted in this example:

<gml:posList>
    42.00 21.15 <!-- (should be 42.0 21.25) -->
    41.30 21.30
    41.45 22.00
    42.17 21.30
    42.00 21.15
</gml:posList>

To Reproduce Steps to reproduce the behavior:

1. Compare https://github.com/wmo-im/iwxxm/blob/master/IWXXM/examples/sigmet-multi-location-VA.tac
2. To https://github.com/wmo-im/iwxxm/blob/master/IWXXM/examples/sigmet-multi-location-VA.xml

Expected behavior The above geometry should be converted as:

<gml:posList>
    42.00 21.25
    41.5 21.5
    41.75 22.00
    42.28333 21.5
    42.00 21.25
</gml:posList>

[mgoberfield]

Hi Paddy,

Can you supply your SIGMET converter output (based on schema v4.0.1) for this example as a pull request?

V/R,

mark

[padhrigmccarthy]

Hi Mark-

Will do.

I know this is off-topic, but do we have an example of a multi-location TC report? If not, should I mock one up and include it in the PR for your approval?

[mgoberfield]

Hi Paddy,

The TAC->XML translations in the examples folders on WMO site were created by hand using the TAC examples found in the Annex 3 documentation.

Other examples, like the one you are proposing, have been posted on the iwxxm-translation site. When you look there, we have a few examples of AIRMETs and SIGMETs based on previous IWXXM releases. There is a TC SIGMET example based SIGMET schema v3.0.0. A PR that illustrates the AIRMET/SIGMET changes (v3.1.1 and v4.0.1 respectively) with the more recent releases of IWXXM would be welcomed but don't feel obligated.

V/R,

mark

[padhrigmccarthy]

Hi Mark-

Getting more and more off-topic here, but do you interpret the 'AND' keyword for repetition in TC reports to join completely separate TC TACs, as in the iwxxm_3.0.0 example you referenced:

    YUDD SIGMET 2 VALID 101200/101800 YUSO-
    YUDD SHANLON FIR TC GLORIA PSN N2100 W06200 CB OBS AT 1200Z WI 20NM
    OF TC CENTRE TOP FL500 WKN FCST AT 1800Z TC CENTRE N2230 W06330 AND
    TC HARRIET PSN N2215 W06100 CB FCST AT 1200Z WI 20NM OF CENTRE TOP
    FL400 WKN FCST AT 1800Z TC CENTRE N2345 W06230

Where each side of the 'AND' will have a complete location, centre, etc? It's not clear from the Annex three documentation that this is allowed for iwxxm 2023-1.

For the VA reports, for example, there is one phenomenon clause (e.g. 'VA CLD') that is then referenced by multiple 'OBS AT ... FCST AT' sections joined by 'AND' keywords. So the phenomenon clause is shared.

Amd81 indicates that neither the 'Phenomenon' nor the 'TC forecast position' can be repeated, which would nullify the **starred** parts of the above report:

    YUDD SIGMET 2 VALID 101200/101800 YUSO-
    YUDD SHANLON FIR TC GLORIA PSN N2100 W06200 CB OBS AT 1200Z WI 20NM
    OF TC CENTRE TOP FL500 WKN FCST AT 1800Z TC CENTRE N2230 W06330 AND
    **TC HARRIET PSN N2215 W06100 CB** FCST AT 1200Z WI 20NM OF CENTRE TOP
    FL400 WKN FCST AT 1800Z **TC CENTRE N2345 W06230**

So this leads me to believe that the 'AND' clause is intended to join multiple locations for a single TC phenomenon. In addition, a named TC can have only one forecast 'TC CENTRE'. So this makes me puzzled about the utility of using the 'AND' keyword with TC reports. I'm thinking it could be used to indicate the observed and general location of the TC or CB at multiple heights, without specifying more than one 'TC CENTRE' location:

    YUDD SIGMET 2 VALID 101200/101800 YUSO-
    YUDD SHANLON FIR TC GLORIA PSN N2100 W06200 CB OBS AT 1200Z WI 20NM
    OF TC CENTRE TOP FL500 WKN FCST AT 1800Z TC CENTRE N2230 W06330
AND OBS AT 1200Z WI 20NM OF N2245 W06345 TOP FL400 WKN FCST AT 1800Z 
    WI N2230 W06330 - N2230 W06430 - N2330 W06430 - N2230 W06330

... where all the the OBS and FCST text refers to location and TOPs of the single CB phenomenon for TC GLORIA, except for the 'FCST AT 1800Z TC CENTRE N2230 W06330' clause which specifies a forecast for the center of the storm. It all seems rather error-prone.

Do you know the intent of the 'AND' repetition keyword for use in TC reports? And am I on track in how I'm interpreting Amd81?

We can take this discussion offline if that would be better. Thank you.

[mgoberfield]

Hi Paddy,

Yeah, the questions just keep coming, and we're getting off-track here. 😄

If you could just submit your corrections about the SIGMET example lat/lon values as a PR that would be fine. As for your SIGMET questions, I can't answer them. Maybe someone else can. If you have any further questions for me, let's take them offline.

V/R,

mark

[jkorosi]

Hi Paddy,

The structure of TC SIGMET was changed from AMD 79, as indicated by the small note under Table A6-1A. You can find the related discussion at https://github.com/wmo-im/iwxxm/discussions/267.

[image: image.png]

Best regards, Jan

Mr. Jan Korosi @.***)

--

Team Leader

IBL Software Engineering, http://www.iblsoft.com/

Galvaniho 17/C, 82104 Bratislava, Slovakia

Phone: +421-2-32662111, Fax: +421-2-32662110

Direct: +421-2-32662152

On Mon, Dec 2, 2024 at 8:14 PM Mark Oberfield @.***> wrote:

Hi Paddy,

Yeah, the questions just keep coming, and we're getting off-track here. 😄

If you could just submit your corrections about the SIGMET example lat/lon values as a PR that would be fine. As for your SIGMET questions, I can't answer them. Maybe someone else can. If you have any further questions for me, let's take them offline.

V/R,

mark

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[amilan17]

https://github.com/wmo-im/iwxxm/wiki/TT-AvData-Discussion-2025-Jan-22 notes: Only the SIGMET TAC example needs to be fixed; FT2025-2

[amilan17]

https://github.com/wmo-im/iwxxm/wiki/TT-AvData-Discussion-2025-Jan-22 notes:

still to be done

[blchoy]

Fixed all positions in sigmet-multi-location-VA.xml in 2025-2RC2.