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Thu Aug 24 01:45:16 2017

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QGIS Planet

Docker basics with Geodocker GeoServer

Today’s post is mostly notes-to-self about using Docker. These steps were tested on a fresh Ubuntu 17.04 install.

Install Docker as described in https://docs.docker.com/engine/installation/linux/docker-ce/ubuntu/ “Install using the repository” section.

Then add the current user to the docker user group (otherwise, all docker commands have to be prefixed with sudo)

$ sudo gpasswd -a $USER docker
$ newgrp docker

Test run the hello world image

$ docker run hello-world

For some more Docker basics, see https://github.com/docker/labs/blob/master/beginner/chapters/alpine.md.

Pull Geodocker images, for example from https://quay.io/organization/geodocker

$ docker pull quay.io/geodocker/base
$ docker pull quay.io/geodocker/geoserver

Get a list of pulled images

$ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
quay.io/geodocker/geoserver latest c60753e05956 8 months ago 904MB
quay.io/geodocker/base latest 293209905a47 8 months ago 646MB

Test run quay.io/geodocker/base

$ docker run -it --rm quay.io/geodocker/base:latest java -version
java version "1.8.0_45"
Java(TM) SE Runtime Environment (build 1.8.0_45-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.45-b02, mixed mode)

Run quay.io/geodocker/geoserver

$ docker run --name geoserver -e AUTHOR="Anita" \
 -d -P quay.io/geodocker/geoserver

The important options are:

-d … Run container in background and print container ID

-P … Publish all exposed ports to random ports

Check if the image is running

$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
684598b57868 quay.io/geodocker/geoserver "/opt/tomcat/bin/c..." 
2 hours ago Up 2 hours 0.0.0.0:32772->9090/tcp geoserver

You can also check which ports to access using

$ docker port geoserver
9090/tcp -> 0.0.0.0:32772

Geoserver should now run on http://localhost:32772/geoserver/ (user=admin, password=geoserver)

For more tests, let’s connect to Geoserver from QGIS

All default example layers are listed

and can be loaded into QGIS


WMS-T Support in Geoserver and Mapserver

“-T”, this small appendix can be found after many popular GIS-related acronym. But of course, it always means something different. Take for example GIS-T (GIS for Transportation), WFS-T (Transactional WFS) and WMS-T (WMS with time support). The world of acronyms is a fun place!

Let’s see what a WMS-T can do for us. From the WMS standard:

Some geographic information may be available at multiple times (for example, an hourly weather map). A WMS
may announce available times in its service metadata, and the GetMap operation includes a parameter for
requesting a particular time
. [...] Depending on the context, time
values may appear as a single value, a list of values, or an interval, …

Currently, only Mapserver supports WMS-T but the Geoserver team is working on it.

Mapserver

MapServer 4.4 and above provides support to interpret the TIME parameter and transform the resulting values into appropriate requests.

Time attributes are specified within the metadata section:

METADATA
"wms_title" "Earthquakes"
"wms_timeextent" "2011-06-01/2011-07-01"
"wms_timeitem" "TIME"
"wms_timedefault" "2011-06-10 12:10:00"
END

Mapserver supports temporal queries for single values, multiple values, single range values or even multiple range values:

...&TIME=2011-06-10&...
...&TIME=2011-06-10, 2004-10-13, 2011-06-19&...
...&TIME=2011-06-10/2011-06-13&...
...&TIME=2011-06-10/2011-06-15, 2011-06-20/2011-06-25&...

Geoserver

GeoSolutions has developed support for TIME and ELEVATION dimensions in WMS.
There are plans to backport this feature to the stable 2.1.x series after the 2.1.1 release.

Configuration of time-enabled layers can be done via the normal user interface:

The following video by GeoSolutions demonstrates the use of Geoserver’s WMS-T:

Both server solutions seem to support only one time attribute per layer. An optional second time attribute would be nice to support datasets with start and end time like Time Manager for QGIS does.


Picking a Feature’s Attribute Value From a WMS Layer With OpenLayers

There are many nice examples out there of how to use a getFeatureInfo request in OpenLayers to display a feature’s attribute table. In some applications it can be useful though not to display the full attribute table but to only select one attribute value from it and output it somewhere, e.g. in a text field.

This post describes how to pick the road id from a road wms layer and write the id value into a text input field.

OpenLayers offers a convenient class to achieve this: OpenLayers.Control.WMSGetFeatureInfo.

Let’s create an object of this class, register and activate it:

roadidPicker = new OpenLayers.Control.WMSGetFeatureInfo({
                url: 'http://localhost:8080/geoserver/wms',
                title: 'identify features on click',
                layers: [wms],
                queryVisible: true
            });
roadidPicker.infoFormat = 'application/vnd.ogc.gml';
roadidPicker.events.register("getfeatureinfo", this, pickRoadid);
map.addControl(roadidPicker);
roadidPicker.activate();

Now, every time the user clicks onto the map, a getFeatureInfo request is issued and the function pickRoadid() is called. In pickRoadid(), we’ll define which value we want to pick from the feature. The ‘id’ of the feature will be written into a text input field called ‘roadId’:

function pickRoadid(e) {
  if (e.features && e.features.length) {
     var val = e.features[0].attributes.id;
     document.getElementById('roadId').value = val;
  }
}

You might have noticed the ‘[0]‘. That’s because the click event comes with a list of features within the reach of the mouse click. For my application, I can only use one value and the first feature in this list is as good as any.


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