Inverted GRIB display

[Moo]

Discovered this one today.

I opened a GRIB file (an ECMWF file downloaded with TZ Navigator v3) which I generally use to access and view/analyse the very good Euro weather model.

When I open this in OCPN the GRIB display is inverted north to south. I have tried numerous file and see the same result in all from this source.

Can others confirm this please? Any files from other sources affected the same way?

Please see attached screenshots and sample file (remove .avi extension).

[hoolie]

I'm not sure what we're looking at here. Both images are OpenCPN and, according to the file reference bottom left, are two different GRIB files. It does not appear to be an inversion, more like a day apart as the wind barbs are generally in the same direction?

[Moo]

Originally Posted by hoolie

I'm not sure what we're looking at here. Both images are OpenCPN and, according to the file reference bottom left, are two different GRIB files. It does not appear to be an inversion, more like a day apart as the wind barbs are generally in the same direction?

It is an inversion.. Same day, same time, same generation time.

[hoolie]

It's not an inversion as the wind barbs are generally similar and the isobars are shaped differently, even if they were inverted. It doesn't look like an OpenCPN problem from the images you've shown. How do they look on a different scale?

[Moo]

trying to post the file again . remove .pdf

[Moo]

Fek it the forum keeps saying that the file is an invalid video when I post it with .pdf extension.

Anyway hoolie here is the same file displayed in TZ Navigator. Can you see that it is inverted yet?

[hoolie]

I think we're talking at cross-purposes. By "inverted" I assumed you meant "upside-down". They're not.

The wind barbs are very similar and generally point in the same direction but the isobar low is in a different place. This is what I would expect if you have a time shift between the two GRIB files. Agreed the shape is similar if it was inverted but by no means an accurate mirror image.

You've shown a TZ image for one of the GRIB files. What does it look like with the other?

[Moo]

Originally Posted by hoolie

I think we're talking at cross-purposes. By "inverted" I assumed you meant "upside-down". They're not.

The wind barbs are very similar and generally point in the same direction but the isobar low is in a different place. This is what I would expect if you have a time shift between the two GRIB files. Agreed the shape is similar if it was inverted but by no means an accurate mirror image.

You've shown a TZ image for one of the GRIB files. What does it look like with the other?

Yes agreed some misunderstanding.. The isobars are inverted.

If there was a time shift the wind arrows would change direction to match the isobars

Here is the GFS in TZ Navigator it displays correctly.

I know TZ Navigator v3 handles both file formats correctly as I usually compare GFS from Saildocs with ECM from Timezero when on passage.

[Moo]

One more try with the GRIB file. replace .pdf with .grb.bz2

[did-g]

Originally Posted by Moo

One more try with the GRIB file. replace .pdf with .grb.bz2

How big is it?

Likely I know what's going on but it'd be a lot easier with a grib file for testing.

[Moo]

Originally Posted by did-g

How big is it?

Likely I know what's going on but it'd be a lot easier with a grib file for testing.

500k.. I have tried with a smaller, and bigger, files but I keep getting the same result from the forum. Can you PM me an email address and I can send the file to you.

[hoolie]

I agree there's a difference with the OCPN ECM file image but it's certainly not simply an inversion. For example the winds off the NE coast of NZ NI are quite different on that GRIB compared with the other three images.

I still think it's a time shift problem. What is the time span of the ECM GRIB file? Maybe OCPN is picking up incorrectly timed data? Can you try other dates/times from that GRIB file with TZ to see whether you can match the OCPN image?

[Moo]

Originally Posted by hoolie

I agree there's a difference with the OCPN ECM file image but it's certainly not simply an inversion. For example the winds off the NE coast of NZ NI are quite different on that GRIB compared with the other three images.

I still think it's a time shift problem. What is the time span of the ECM GRIB file? Maybe OCPN is picking up incorrectly timed data? Can you try other dates/times from that GRIB file with TZ to see whether you can match the OCPN image?

Have a think about which direction the air circulation is around a LP in the southern hemisphere, then look again.

[hoolie]

I know the physics! Three of your images show 40kn north north west wind off the NE coast of NZ NI. The ECM OCPN you're complaining about shows 10kn south easterly

[did-g]

Originally Posted by hoolie

I agree there's a difference with the OCPN ECM file image but it's certainly not simply an inversion. For example the winds off the NE coast of NZ NI are quite different on that GRIB compared with the other three images.

I still think it's a time shift problem. What is the time span of the ECM GRIB file? Maybe OCPN is picking up incorrectly timed data? Can you try other dates/times from that GRIB file with TZ to see whether you can match the OCPN image?

There's various way you can read grib grid data, left to right, right to left, top to bottom, bottom to to top and so on. If ECM files are using an order we've never seen before OCPN could be 'confused'.