New Grib Presentation

[rgleason]

Quote:
Originally Posted by rgleason
The grib_pi got hung up on an old RTOFS file which does not have Wind and I had to wait to shutdown Opencpn and restart, but that file might be corrupted.

Sean

I don't care if the file is corrupted if the program gets stuck then we should fix that. Can you post the file?

Sure, here is one that hangs eventually for me. OpenCPN freezes.

It is too big to upload here so it will be in the main directory of
Opencpn Beta File Thingie rguser rgpass

RTOFS20150619174405933.grb.doc

[rgleason]

In updating the Grib_pi plugin for various small improvements, one improvement is to fixed and minimum spacing. In windows the menu is not free to shrink vertically and there is too much empty space when I take a screenshot.

Can someone add the ability to shrink the menu vertically?
It will help us get meaningful images for the documentation.

(Linux screenshots are better, because the space is closed up, but I don't run that.)

Thanks

[rgleason]

For Grib_pi, In windows, the menu is not free to shrink vertically and there is too much empty space when I take a screenshot. It would be even better if the space was automatically eliminated, and the Menu would automatically adjust to what is needed.

----
HOWEVER, I don't need it now. I have cut out the blank areas in the screenshots.

[rgleason]

Originally Posted by boat_alexandra

Does anyone know of a web access to grib files we can support in the plugin? It would be faster and more automatic than email.

Sean, would this do it?
An entire set of instructions using get, wget etc.
Fast Downloading of GRIB Files Partial http transfers
http://www.cpc.ncep.noaa.gov/product...ding_grib.html

[rgleason]

Maitai's post on grib sources
http://www.cruisersforum.com/forums/...ml#post2534452

FYI following some discussions on other topics with skiron people, they agreed to make their directories index-able, so you can now use in qtVlm customized grib download these addresses:

Index of /gribs_wrf_4km
Index of /gribs_wrf_12km
Index of /gribs_skiron
Index of /saildocs

[seandepagnier]

Am I missing something, or the "partial grib" described only allows various fields (eg, precipitation, wind etc) it doesn't allow partial geographic regions which is what we really need.

Fast Downloading of GRIB Files

[bdbcat]

Sean/Rick...

This server is what we use in Android. One can specify the geographical area, parameters of interest, time scale, etc.

Works fine, for what is does. Has lots of parameters. 3 model grids (1.0, 0.5, and 0.25 degree)

So far, very reliable.

Dave

[rgleason]

Dave, Thanks for your post. This is great to know. I just wrote Wesley at Noaa asking how we define a select area. Can you please advise how this is done, perhaps with an example call?

Maybe then Sean or Ptizif can program a direct request for Grib_pi?

-Sean, hope you are in a warmer climate and comfortable.

[bdbcat]

Rick...

What one does is to "craft" a specific URL containing the lat/lon, parameters required, etc. When that URL is accessed, the NOAA server prepares the file on demand.

Here is a sample URL from Android GRIB fetch. You can try the URL manually in browser, catch the GRIB file, and show it like normal. Note the "subregion" parameters. This sets the coverage area desired.

So, the fiddly work activity is to build code to craft the URL conforming to the user's specified parameters.

http://nomads.ncep.noaa.gov/cgi-bin/...gfs.2017121206


Good Luck
Dave

[rgleason]

Thank you Dave.

nomads.ncep.noaa.gov/cgi-bin/filter_gfs_1p00.pl?file=gfs.t06z.pgrb2.1p00.f000&v ar_UGRD=on&var_VGRD=on&lev_10_m_above_ground=on&su bregion=&leftlon=-85&rightlon=-74&toplat=34&bottomlat=21&dir=%2Fgfs.2017121206

on&subregion=
&leftlon=-85
&rightlon=-74
&toplat=34
&bottomlat=21

I found a 1k file in my browser download gfs.t06z.pgrb2.1p00.f000
Which when I add .grb to the end, shows up in the Grib_pi and loads, showing below.

We now have a path to create direct downloads in grib_pi!

[rgleason]

The Fast Downloading Page has a Sample script which downloads a time span.

do
url="http://nomad3.ncep.noaa.gov/pub/reanalysis-2/6hr/pgb/pgb.$date"
get_inv.pl "${url}.inv" | grep ":VGRD:" | grep ":10 mb" | \
get_grib.pl "${url}" pgb.$date
date=$(($date + 1))
if [ $(($date % 100)) -eq 13 ] ; then
date=$(($date - 12 + 100));
fi
done

[rgleason]

The second page of Fast Downloading shows a script get_gfs.pl. that uses perl I believe.

Fast Downloading of GRIB Files, Part 2

I don't have perl on this machine, but perhaps it should be considered.

Part of Wesley's script's header is this

# simple script to download gfs files
# inspired by Dan Swank's get-narr.pl script
# this script uses the tecnique described in
# Fast Downloading of GRIB Files
#
# arguments: action YYYYMMDDHH HR0 HR1 DHR VAR_LIST LEV_LIST DIRECTORY
#
# action = inv (display inventory of 1st file)
# data (get data)
#
# HR0, HR1, DHR: forecast hour parameters
# do f_hour = HR0, HR1, DHR (fortran)
# for (f_hour = HR1; f_hour <= HR1; f_hour = f_hour + DHR) (C)
#
# VAR_LIST: list of variable separated by colons, blanks replaced by underscore
# ex. HGT:TMP:OZONE
# LEV_LIST: list of levesl separated by colons, blanks replaced by underscore
# ex. 500_mb:sfc
#
# DIRECTORY: name of the directory in which to place the files

[bdbcat]

Rick...

This feature should be built into the Plugin itself, not calling out to a script. External scripts are a sure route to cross-platform incompatibility.

The Plugin API includes methods for arbitrary file download, so all one needs to do is craft the URL(s) (c++ code here), and call the API. Not really trivial, but not impossibly complex either.

Dave

[rgleason]

Dave, thanks. How is the Android App doing it? Would that code help? Maybe I should try the App and see how it works.... Never knew it had that feature!

[bdbcat]

Rick...

On Android, the code to generate URLs and fetch GRIBs is all in java on the Android OS. Java is, well, something like c++, but not exactly. So not directly portable.

Anyway, on Android, we craft the lat/lon limits by simply taking the limits of what is shown on the screen at the time of the request.

I assume on desktop we want the user to drag a rectangle region on the chart to select the area of interest. Not difficult, but will require an experienced c++/wxWidgets plugin author to build.

Dave