{"id":5467,"date":"2018-06-07T06:35:11","date_gmt":"2018-06-07T04:35:11","guid":{"rendered":"http:\/\/www.sigterritoires.fr\/?p=5467"},"modified":"2023-04-28T14:58:03","modified_gmt":"2023-04-28T12:58:03","slug":"how-to-integrate-free-marine-and-terrestrial-weather-forecasts-into-qgis","status":"publish","type":"post","link":"https:\/\/www.sigterritoires.fr\/index.php\/en\/how-to-integrate-free-marine-and-terrestrial-weather-forecasts-into-qgis\/","title":{"rendered":"How to integrate free marine and terrestrial weather forecasts into QGis"},"content":{"rendered":"

In the previous article we discussed\u00a0How to integrate free marine and terrestrial weather forecasts into\u00a0ArcGis<\/a>.
\nIn this article we will discuss how to integrate weather forecasts into a\u00a0QGis\u00a0project\u00a0.\u00a0We will use marine forecast data for 8 days.\u00a0These data is provided by the companies\u00a0\u00a0\u00a0 NASCA<\/a>\u00a0\u00a0\u00a0and\u00a0\u00a0\u00a0 ACTIMAR<\/a>\u00a0, via the products\u00a0\u00a0enav-forecast\u00a0.\u00a0Besides the software that employs and shares these forecasts for consultation and analysis (\u00a0 enav-viewer<\/a>\u00a0,\u00a0\u00a0\u00a0enav-forecast\u00a0,\u00a0\u00a0\u00a0enav-forecast\u00a0for iPhone\u00a0,\u00a0\u00a0\u00a0enav\u00a0-Pilot\u00a0), these companies also provides you with access to data via a WFS connection.<\/p>\n

What data is available?<\/strong><\/p>\n

Regarding the data type, you access the 8-\u00a0day\u00a0forecasts,\u00a0every 3 hours, for the following parameters:<\/p>\n

\n
height (in meters)\u00a0, direction\u00a0(in \u00b0) and wave period (in sec)<\/li>\n
crossed sea (wave direction in \u00b0\u00a0, direction\u00a0of the swell in \u00b0)<\/li>\n
speed (in\u00a0knots\u00a0) and direction (in \u00b0) of the average wind<\/li>\n
speed (in\u00a0knots\u00a0) of wind gusts<\/li>\n
speed (in\u00a0knots\u00a0) and direction (in \u00b0) of the surface current<\/li>\n
temperature (in \u00b0 C) of the sea surface water<\/li>\n
temperature (in \u00b0 C) of the air<\/li>\n

rainfall (in mm)<\/li>\n<\/ul>\n
Which data grid?<\/strong><\/p>\n
The grid of free forecasts is of 0.5 \u00b0.\u00a0Other grids are available but subject to subscription (see subscriptions).
\nThe forecasts cover the whole world.<\/p>\n
Update Frequency <\/strong><\/p>\n
The forecasts are updated four times a day.<\/p>\n
How to set up the WFS connection<\/strong><\/p>\n
To set up a WFS connection you click on the button \u00ab\u00a0Add a WFS layer\u201d, then click on the button \u201cNew\u201d\u00a0to create the connection parameters.<\/p>\n
$\"\"$ <\/p>\n
For the name type a high tech option: NASCA Marine Weather, for example.
\nFor the URL, enter the following string:
\nClick OK to close the configuration.
\nThe connection now appears in the list of possible connections.<\/p>\n
Before you log in<\/strong><\/p>\n
Open a project with the WGS84 Geographic SCR.\u00a0Display a base map that allows you to zoom in on the area of \u200b\u200binterest.\u00a0When you connect to the WFS server,\u00a0QGis\u00a0will send a query with the coordinates of the four corners of your current display.\u00a0The server will send the available forecasts inside this rectangle to your machine.<\/p>\n
If you are working in projection<\/a> mode (and not geographical), neither\u00a0QGis\u00a0nor the server will make a coordinates transformation. You\u00a0will have no result in return, often, not even an error message.<\/p>\n
Therefore it must be verified that what you are going to transmit are latitude and longitude coordinates in degrees.\u00a0To do that, simply, look at the status bar at the bottom of the QGis window: you have a field called \u201ccoordinates\u201d.\u00a0The values \u200b\u200bin this field must be between -180 and 180. If this is the case, you are working with geographic coordinates.<\/p>\n
If you are working with geographical coordinates but if you do not zoom in on the area of \u200b\u200binterest, you may have an area too big for the query.\u00a0In addition to being time consuming, WFS servers always have a limit for the number of records.\u00a0When this limit is reached, \u00a0the server sends the records found and then stops.\u00a0You will not have a warning message, just the data will be cut.<\/p>\n
Logging in to the WFS server<\/strong><\/p>\n
Then, a new connection appears in the list of proposed connections when you click on the button \u00ab\u00a0Add a WFS layer\u00a0\u00bb.\u00a0Click on the button \u00ab\u00a0Log in\u00a0\u00bb.<\/p>\n
$\"\"$ <\/p>\n
You will only use the layer: view_meteo99<\/p>\n
Click on this line to select it.\u00a0Uncheck the box \u201cCache\u00a0feature\u201d.
\nClick on \u00ab\u00a0Add\u00a0\u00bb.<\/p>\n
Displaying forecast data<\/strong><\/p>\n
After a few moments, the new layer is added to the\u00a0QGis\u00a0map window.<\/p>\n
$\"\"$ <\/p>\n
Each \u201cpoint\u201d\u00a0of the forecast is, actually, an array of 66 points.\u00a0To be able to view the forecasts for a given hour, you will have to make a selection on all the data for each point.\u00a0Performing this job for all the requests \u00a0is rather complicated and not worth it.\u00a0The most efficient method is to display all the data in\u00a0QGis\u00a0and create a new layer on your workstation.<\/p>\n
You can perform this task directly by clicking on the legend of the layer and selecting \u00ab\u00a0Save as …\u00bb\u00a0But do not rush, there are other little things to fix, and we’ll do it all at once.<\/p>\n
The WFS connections with\u00a0QGis\u00a0have a small flaw: according to the first value found for an attribute field of the\u00a0table,\u00a0it defines the data type.\u00a0Often we are left with numeric fields in the original table of the server, but QGis reads them as text strings. When working with marine forecasts, the problem does not arise for the values \u200b\u200bof force and speed, which are always\u00a0values \u200b\u200bwith a decimal point.\u00a0On the other hand, for direction values, which are depicted by natural numbers, the problem arises.
\nYou will have direction values \u200b\u200bas a\u00a0text\u00a0string.\u00a0While\u00a0for a simple display it does not change much, when displaying oriented arrows (currents, waves, wind) it is impossible to request a rotation of the symbol with a text field.\u00a0It is imperative that the direction field be numeric.<\/p>\n
To solve this problem, you must create a new numeric field and use the calculator field to work out the values \u200b\u200bfrom the text strings for, and repeat this task for the three direction fields (wave, wind, current).<\/p>\n
Tedious work.\u00a0So, a simpler solution must be found.\u00a0We have to build a processing model with the QGis \u00ab\u00a0Graphic modeler\u201d.\u00a0This is a small file that you can download by clicking\u00a0here<\/a>\u00a0.<\/p>\n
Unzip the file into a directory of your choice.<\/p>\n
Open the Chart Modeler:<\/p>\n
$\"\"$
\nIn the Modeler window, click the first button to open the downloaded template.\u00a0Point to the\u00a0meteoNasca.model\u00a0file.
\nThe model loads.<\/p>\n
$\"\"$ <\/p>\n
To execute it, click on the right button \u201cLaunch the model\u00a0\u00bb.<\/p>\n
$\"\"$ <\/p>\n
Check that the input file is the layer \u00ab\u00a0view_meteo99\u00a0\u00bb.
\nBrowse the directories to define the location and name of the\u00a0shape\u00a0file\u00a0that will be created on your\u00a0computer. Select\u00a0\u00ab\u00a0Save to file\u00a0\u00bb
\nClick on\u00a0Run
\nThe new layer is loaded in the map window.\u00a0You can now delete the WFS layer, it avoids loadings each time you\u00a0change\u00a0the grip of the view.<\/p>\n
$\"\"$ <\/p>\n
Symbology<\/strong>\u00a0of forecast data<\/strong><\/p>\n
For simple data (temperature, rainfall, …) the only thing to remember is that you have 66 points superimposed on each forecast location.\u00a0You must go through a \u00ab\u00a0subset query\u201d\u00a0in order to show just\u00a0 one step at a time\u00a0:
\nLayer properties -> \u00a0\u00bb\u00a0\u00a0\u00a0General\u00a0\u00a0\u00a0\u00bb-> Subset (click on query builder)<\/p>\n
$\"\"$ <\/p>\n
You have two attributes, the first for today’s date, the second for the time of day.\u00a0\u00a0<\/strong>\u00a0WARNING!<\/strong>\u00a0Time is depicted as GMT not in local time.<\/strong><\/p>\n
Before applying the\u00a0symbology, do not forget to define the selection request.\u00a0If not, you will have a stack of symbols on each point.<\/p>\n
For complex data (wind, waves, current) you have at least two associated values: direction and strength.\u00a0The classic way to display this type of data is to use an arrow oriented in the direction of the phenomenon and to assign it either a size or a different colour depending on the force.<\/p>\n
First thing to know: How is the direction of the phenomenon coded?
\nAll directions present in the attributes of the table indicate the direction from which the phenomenon originates (the direction from which it comes).
\nTo position the arrows, it is necessary to apply a rotation to the symbol.\u00a0If you choose a symbol \u201cup arrow\u201d\u00a0and you enter as rotation field only the name of the direction field, your arrows will indicate the opposite direction!\u00a0In this case, use an expression, for rotation, such as [direction field] – 180.<\/p>\n
We have prepared three layer files with\u00a0standard\u00a0symbology\u00a0that should do the trick.\u00a0You can download them in\u00a0\u00a0\u00a0here<\/a>\u00a0.
\nIn the compressed file, you have three\u00a0Qgis\u00a0layer style\u00a0files\u00a0(wind, current and waves) and a folder with the symbols used for the wind in the weather charts (barbules).
\nThe first three can be extracted in the directory of your choice.\u00a0On the other hand, the file\u00a0\u00a0\u00a0\u201cbarbules\u201d\u00a0\u00a0\u00a0has to be copied in the QGis\u00a0\/\u00a0apps\u00a0\/\u00a0qgis\u00a0\/\u00a0svg\u00a0 installation directory.\u00a0Otherwise, the symbols will not be accessible for style files.<\/p>\n
The\u00a0symbology\u00a0for the wind is as follows:<\/p>\n
$\"\"$ <\/p>\n
The symbols used are standard barbules, with increments of knots up to 65 knots.
\nThe rotation field is already corrected to depict the correct orientation of the barbules.<\/p>\n
The\u00a0symbology\u00a0for the current is as follows:<\/p>\n
$\"\"$ <\/p>\n
The symbols used are\u00a0arrows,\u00a0with increments of 1 knot.\u00a0The size of the arrows increases according to the speed.\u00a0Moreover speeds up to 3 knots are in blue, between 3 and 5 are in orange and from 6 knots in red.
\nThe rotation field is corrected by 180 \u00b0 to have the correct direction of the arrows.
\nRemember to add in the selection request, besides date and time, a filter on direction and speed so as not to display the null values at ground level (\u00a0CourantVal<\/strong>\u00a0<> 0 ANDICurDir<\/strong>\u00a0<> 0<\/strong>\u00a0).<\/p>\n
The\u00a0symbology\u00a0for the waves is as follows:<\/p>\n
$\"\"$ <\/p>\n
The symbols used are\u00a0arrows,\u00a0with increments of 1 meter.\u00a0Heights of up to 3 meters are green, between 4 and 7 are yellow and from 7 knots are orange-red.
\nThe rotation field is corrected by 180 \u00b0 to have the right direction of the arrows.
\nRemember to add in the selection request, besides date and time, a filter on the direction and speed so as not to display the null values at ground level (\u00a0HsVal<\/strong>\u00a0<> 0 AND<\/strong>\u00a0IHsDir<\/strong>\u00a0<> 0<\/strong>).
\nThe labels indicate the significant height of the waves in meters, and the wave period in seconds.<\/p>\n
If you have any doubt, do not hesitate to leave a comment!<\/p>\n
\n
<\/li>\n<\/ul>\n
<\/p>\n
<\/p>\n","protected":false},"excerpt":{"rendered":"
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