Weather for a region is not positioned correcly

[turban]

Thanks for a great plugin!

I've created wind data for a region and added to a Leaflet map using this plugin:
http://mastermaps.com/racetracker/hardangervidda.html

I'm reading the bounds from the JSON-file and they are correct when I draw a rectangle and zoom the map to these bounds. The wind layer is displayed below the correct position:

Is this a know issue?

[brentfraser]

The problem is the "scanMode" in the json (and grib) file. Currently only scanMode: 0 is supported.
If your scanMode: 64, a quick fix is to modify the json file to set "dy": -0.25 so the Y direction is incremented in the opposite direction.

A better fix is to modify the leaflet-velocity JavaScript to interpret the scanMode and adjust the parameters appropriately (and maybe just support a subset of scanModes). For example, around line 530:
if (header.scanMode === 64) Δφ = -Δφ;

But really we should decode the scanMode bits and give a message for those we don't support.

[brentfraser]

FYI. some links
https://www.nco.ncep.noaa.gov/pmb/docs/grib2/grib2_doc/grib2_table3-4.shtml
https://www.unidata.ucar.edu/mailing_lists/archives/netcdf-java/2015/msg00001.html
https://trac.osgeo.org/gdal/ticket/2550

[brentfraser]

A slightly better (but not tested) fix, at line 530:

    
    var scanModeMask = header.scanMode.toString(2)
    scanModeMask = ('0'+scanModeMask).slice(-8);
    var scanModeMaskArray = scanModeMask.split('').map(Number).map(Boolean);
    var supported = true;	
    if (scanModeMaskArray[0]) Δλ =-Δλ;
    if (scanModeMaskArray[1]) Δφ = -Δφ;
    if (scanModeMaskArray[2]) supported = false;
    if (scanModeMaskArray[3]) supported = false;
    if (scanModeMaskArray[4]) supported = false;
    if (scanModeMaskArray[5]) supported = false;
    if (scanModeMaskArray[6]) supported = false;
    if (scanModeMaskArray[7]) supported = false;
    if (!supported) console.log("Data with scanMode: "+header.scanMode+ " is not supported.");

[d03090]

Thank you very much for this solution! I was struggling with this scanMode as well. So, this worked fine for me!

Still not exactly sure why scanMode 64 (01000000) affects Bit No. 2 and not No. 7 though (why is this flipped?).

[brentfraser]

I think it is a LSB/MSB thing. I guess I could reorder the scanModeMaskArray in the above code to match the bits in the table https://www.nco.ncep.noaa.gov/pmb/docs/grib2/grib2_doc/grib2_table3-4.shtml

[turban]

Thanks @brentfraser! Your quick-fix solution worked :-)

[danwild]

Thanks @brentfraser, please consider putting in a PR.