Sourcepole - Linux & Open Source Solutions

Sourcepole - Linux & Open Source Solutions

QGIS Cloud and Sourcepole are proud to be official sponsors of the team Öcher-Safari, attending the Allgäu-Orient-Rallye. One of the last adventures in the world of cars. Sourcepole serves the team with know how, infrastructure and more. Information about the team and the charity ideas of this event you can find on Öcher-Safari and the official web site of the Allgäu-Orient-Rallye.

We’ll be using Postgis2.0 from UbuntuGIS, which has packages for a number of recent Ubuntu releases. Since Ubuntu precise has libc6 2.14 and Debian wheezy only 2.13 we fall back on Ubuntu oneiric for packages, which also has libc6 2.13.

However Postgis 2.0 in UbuntuGIS depends on a lot of llibraries which were in squeeze but live in wheezy under a higher version. Therefore we’ll install a lot of packages from Debian squeeze. Fortunately the libraries are versioned themselves and thus can be installed along the libraries from Debian wheezy.

Let’s go. Add the Debian squeeze sources:

# SRC="deb http://ftp.ch.debian.org/debian/ wheezy main"
# echo "$SRC" >> /etc/apt/sources.list

We’ll also add the security source, in case Debian releases a security update.

# SRC="deb http://ftp.ch.debian.org/debian/ wheezy main"
# echo "$SRC" >> /etc/apt/sources.list

You may want to replace ftp.ch.debian.org by a debian mirror nearer to you.

Now add the UbuntuGIS sources:

# SRC="deb http://ppa.launchpad.net/ubuntugis/ubuntugis-unstable/ubuntu oneiric main"
# echo "$SRC" > /etc/apt/sources.list.d/ubuntugis.list

Now update and try to install postgis:

# apt-get update
# apt-get install postgresql-9.1-postgis

Create your database:

# sudo su
# su - postgres
$ psql postgres
postgres=# CREATE DATABASE your_db OWNER your_preferred_user:

Now add the postgis features to that database:

$ psql -d your_db -f /usr/share/postgresql/9.1/contrib/postgis-2.0/
$ psql -d your_db -f /usr/share/postgresql/9.1/contrib/postgis-2.0/spatial_ref_sys.sql

That should be it. Let’s hope it works.

A final warning: you are mixing multiple distributions here. This can lead to problems. Due to version conflicts upgrading packages can become very difficult.

Tomáš Pospíšek tpo_hp@sourcepole.ch

The Region of Umbria, Italy, sponsored 4 days of work to update QGIS Globe for current QGIS versions. Most of the functionality is working again and the globe is now compatible with osgEarth 1.0 up to 1.3. The bad news is, that the globe plugin is not working on Windows with OSGeo4W. It seems that one of the OSGeo4W libraries (GDAL?) is compiled with an incompatible MS compiler version. Christmas holidays are coming…

At least it gives Linux users the possibility to play with the globe using the current development version and do exciting stuff like Oslandia does:

PostGIS 3D demo

Imagine someone would sponsor four weeks of QGIS Globe work!

In QGIS server, it is now possible to selectively exclude layers from WMS publication. These layers will be available only on the desktop and hidden from WMS clients. Similarly, print layouts can be excluded from WMS publication. Of course, these settings are conveniently accessible from the project properties dialog of QGIS (but you need to have a nightly build or a recent compile):

Additionally, attributes per layer can be excluded from WMS or WFS publication in the vector properties dialog:

There is also a new request type called ‘GetProjectSettings’. The output of this request is similar to the GetCapabilities output, but with more details and more specific to QGIS:

• Initial visibility of layers
• Information about vector attributes and their edit types
• Information about layer order and drawing order
• List of layers published in WFS

These new features have been developed in collaboration and with funding from the city of Uster. More details are available on the QGIS server / webclient wiki page

For providing maps via WMS over the internet, it is important to generate image files with a small size. Because normally, most of the perceived WMS delay comes from transfering large images files over the internet (and not from map rendering itself). Therefore, QGIS server supports the conversion of png24 and png32 images into png8, therefore generating a file with only 1/3 resp. 1/4 of the original size (but with lower quality). However, until recently, QGIS server was using the default algorithm from the Qt library for conversion to png8, resulting in very ugly png8 images if used with a transparent background and sometimes with shifted colors. Therefore, I decided to implement a better conversion algorithm: the median cut algorithm, which was first described by Heckbert in 1982 ( Paul S. Heckbert, Color Image Quantization for Frame Buffer Display. ACM SIGGRAPH ‘82 Proceedings). This algorithm creates color boxes in 4-dimensional colour space and subdivides at the mean of the largest dimension. It stops if the number of boxes equals the requested number of colors (256 in the case of png8 conversion). First tests show the quality of the converted images are quite good for vector maps. So a performant configuration for a webmap means probably to fetch background rasters as jpg and to overlay vectors as png8 with transparent background.

Let’s see with an example what the conversion from png24 to png8 means in terms of image quality. The first file is a png24 image, 590 KB size:

And this one is the conversion to png8, only 190 KB size.

To test the png8 conversion, you need to have the latest QGIS version from git (or a nightly build tomorrow). Then simply replace the FORMAT paramter in the url with ‘&FORMAT=image/png; mode=8bit’.