Tag: en_gb

EN | PT

Now and then I get too many map symbols (points) in the same place, and I thought how nice it would be if we could drag n’ drop them around without messing with their geometries position, just like we do with labels. That thought gave me an idea for a cool hack.

Choose your point layer and start by creating two new fields called symbX and symbY (Type: Decimal number; Size: 20; Precision: 5). Now go the layer properties and in the Style tab edit your symbol. For each level of your symbol select “map units” as the offset units, and set the following expression in the offset data define properties option:

CASE WHEN symbX IS NOT NULL AND symbY IS NOT NULL THEN
    tostring($x - symbX) + ',' + tostring($y - symbY)
ELSE
    '0,0'
END

Be aware that, if your coordinates have negative values, you need to adapt the code. E.g., If you have negative values in X you should use “tostring(symbX -$x)” instead.

Now, temporarly  label your layer with a small convenient text (I used a centered ‘+’ (plus sign) with a white buffer) and set its coordinates to data defined using the symbX and symbY Fields.

From this point on, when you use the move label tool, not only the label position change but also the actual symbol! Pretty cool, isn’t it?

Notice that the features geometries are not changed during the process. Also, remember that in this case you can also add leading lines to connect the symbols to the original position of the points.

Sea Surface Temperature data downloaded by Oceancolor Data Downloader.

The Oceancolor Data Downloader is a new plugin for QGIS from the Mapping and Geographic Information Centre of the British Antarctic Survey that downloads Oceancolor and Sea Surface Temperature data from NASA’s Oceancolor website. The plugin currently downloads three datasets:

• MODIS AQUA chlorophyll concentration
• SeaWiFS chlorophyll concentration
• MODIS AQUA night time Sea Surface Temperatures

The data accessed includes daily, 8 day, monthly and yearly composites, all of which can be saved to disk while downloading. Future plans for the plugin include additional access to other datasets such as ocean Net Primary Production, selection by bounding box, the ability to save in other formats, a progress bar etc.

I used the plugin to download global Sea Surface Temperatures for the 13th Jan 2015. I then used shapefiles from Natural Earth to create a simple basemap. I finally chose the IBCAO Polar Stereographic projection (EPSG: 3996) to create a map centred on the North Pole.

If you use the plugin to produce published research, please cite:

EN | PT

I had the need to add columns with the coordinates of polygons centroids. I came up with the following expressions to calculate X e Y, respectively:

xmin(centroid($geometry))
ymin(centroid($geometry))

The expression seems quite simple, but it toke me some time before I realize that, not having a x(geometry) and y(geometry) functions, I could use the xmin() and ymin() to get the coordinates of the polygons centroids. Since this wasn’t the first time I had to use this expressions, this post will work as a reminder for the future.

A very handy plugin for QGIS I use day to day is go2streetview by Enrico Ferreguti. The plugin adds an icon to the tool bar in QGIS and when selected I can click a road or street on a base map and a window will open that displays the Google Street or a Bing Maps Bird’s Eye view of the location. The camera’s direction and location is highlighted by a blue marker. I use the plugin when tracing boundaries of parks, open spaces and foot paths from aerial imagery. If the imagery is blurred or the view is obscured by trees, I click a point on a nearby street to see the location up close. The plugin works wherever Google Street view and Bing Birds Eye has coverage.

For example, in the screen-shot below notice there is a footpath leading to a bus shelter that’s not mapped by OpenStreetMap. I know where it is now, I will add it to my map.

Plugin: go2streetview

It is with great pleasure that we want to announce the new name for what was briefly known as QGIS mobile.

Please welcome QField for QGIS™!

After long thinking about various names and variants including QGIS mobile, QTouch, OPENGIS.ch QGIS mobile, QWork, and many more, we felt that QField represents best what we want to archive. A field data capture and management app fully compatible with QGIS™ . QField allows you to take your QGIS projects out of the office for effective field work. By maintaining QGIS’ styling and edit widgets QField greatly reduces preparation time. QField is an Open Source project led by OPENGIS.ch LLC with the whole development happening on Github . Currently we are running an invite-only alpha testing but as soon as the app will have a bit more functionality we will widen up the testers group. QField will be released for free on the Playstore with the possibility of donating to the project via paypal  (preferred) or by buying the QField for QGIS Karma edition app . Another way to greatly help the project is, if you need a specific feature, contact us  to sponsor its development. QField is built from ground up to be touch oriented and easy to use outside and follows the following paradigm: ● GPS centric ● QGIS desktop compatible ● Fully working when offline ● Synchronization capabilities ● Project preparation on desktop ● Few and large buttons ● Switchable use paradigm (Display, Digitizing, Measuring, Inspection,…) QField is built using Qt5, QtQuick 2 (both are supported and suggested by Qt) and OpenGL so it is future proof and it spearheads QGIS towards Qt5. For feature requests, please contact us For bug reports contact us or better file an issue on Github

EN | PT

Recently I had the need to add labels to features with very close geometries, resulting in their collision.

Using data-defined override for label’s position (I have used layer to labeled layer plugin to set this really fast) and the QGIS tool to move labels, it was quite easy to relocate them to better places. However, in same cases, it was difficult to understand to which geometry they belonged.

I needed some kind of leading lines to connect, whenever necessary, label and feature. I knew another great plugin called “Easy Custom Labeling“, by Regis Haubourg, that did what I needed, but it would create a memory duplicate of the original layer, wish meant that any edition on the original layer wouldn’t be updated in the labels.

Since the data were stored in a PostgreSQL/Postgis database, I have decided to create a query that would return a layer with leading lines. I used the following query in DB manager:

SELECT
  gid,
  label,
  ST_Makeline(St_setSRID(ST_PointOnSurface(geom),27493), St_setSRID(St_Point(x_label::numeric, y_label::numeric),27493))
FROM
  epvu.sgev
WHERE
  x_label IS NOT NULL AND
  y_label IS NOT NULL AND
  NOT ST_Within(ST_Makeline(St_setSRID(ST_PointOnSurface(geom),27493), St_setSRID(St_Point(x_label::numeric, y_label::numeric),27493)),geom))

This query creates a line by using the feature centroid as starting point and the label coordinate as end point. The last condition on the WHERE statement assures that the lines are only created for labels outside the feature.

With the resulting layer loaded in my project, all I need is to move my labels and save the edition (and press refresh) to show a nice leading line.

QField (formerly known as QGIS Mobile) is a touch optimized interface for field work developed by OPENGIS.ch. It is with great pleasure the we want to share with you the demo video of version 0.2. Since the project is going to be one of our core projects, we set up a dedicated page here . The QGIS mobile 0.2  video demonstrates some basic functionality like navigation, feature identification and attribute editing.

The performance is affected by android’s video recording software. In reality animaitons look fluent and the interface feels snappy. Demo performed on a Galaxy Note 8.0 with Android 4.4.4 (CM11).

For the first time we at OPENGIS.ch can celebrate with 2 people, Marco Bernasocchi and Matthias Kuhn both experienced QGIS developers and holders of a Master degree in GIScience. After having worked individually in the last years, we have realized that there is a huge potential for us to join our knowledge - because the whole is greater than the sum of its parts. This is why starting from January 1st, 2015 we are working together as OPENGIS.ch LLC. Marco is the creator of QGIS for Android, has a strong background in python and web applications development and is core committer of the the award-winning InaSafe project. Matthias is an active QGIS core committer with a long history in developing in a wide variety of programming languages and areas from embedded systems to server services. We both are strong believers in open source software and are convinced that developing in the public is a big win for everybody. Among other projects, we are currently working on QGIS Mobile. A touch optimized interface for field work, based on the QGIS libraries. Make sure you keep an eye on this project as it is in its infancy but growing very fast. If you have a use-case for it and would like to support its development don’t hesitate contacting us. We will happily provide you with a preview version. [embed]https://vimeo.com/116231850[/embed] We are are also available for helping you with any idea and project you might have and to give ad-hoc courses that cover topics related to (Q)GIS and programming.

All the best

Marco and Matthias