Desktop Software API's in Python (KiCAD, FreeCAD, Blender, QGIS)

Python wraps around everything

For the last couple of years I have mostly written Satellite Data Processing code in Python and plenty of Flask/Django web services. However Python is also an excellent automation tool for GUI based applications allowing custom plugins to be written and functionality provided out of the box extended by users.

The first desktop application I seriously looked at Python plugins for was QGIS. It was early days of learning how to wrap C++ code using SWIG/SIP etc. In the old mailing list you can find a much younger me making inane comments about mixing wrapper metaphors in QGIS with SWIG + SIP. We have come a long way since then and SIP based bindings are the mainstay of QGIS plugins.

QGIS

QGIS has so many Python plugins that they need a registry of their own. Occasionally QGIS Python gets twisted around itself due to multiple Pythons in the user enviroment. You can also flip the python API around and instead of building a plugin you can turn QGIS into a custom desktop application. Which is what I have done with my basic Airport Viewer demo.

QGIS being a fairly extensive and complex C++ application which takes hours to compile, being able to make small quick changes in python is invaluable.

KiCAD

At the time of writing KiCAD has an extensive Python API for processing the automating the PCB layout part of the workflow and this has lead to many innovations in automating traditionally laborious hand layout or even performing complex simulations / optimization to set trace lengths. For example Josh Johnson has one for laying parts out in a circle and Greg Davill has several for length matching and rendering file generation. My personal favourite among the KiCAD scripts is the one for generation of Interactive BOM.

I am really looking forward to Python script support in the Schematic Editor. Meanwhile programmatic Schematic generation tools like Skidl provide schematic oriented Python fun.

The rendering of the PCB's is often done in Blender. Which has its own set of Python nicities.

Blender

My first foray in creating a Blender API based application was during the Kinect USB protocol hacking days. The data stream had just been decoded and I wanted an easy pipeline to a commonly installed / open-source 3D display software. The Python API is mature enough for people these days to quickly put together motion capture plugins for Blender. This plugin however demonstrates the challenges for creating native plugins for blender, the .pyd files for Python have to be recreated for different versions of Blender for ABI compaitibility.

Getting the binaries working has had me thrashing about and posting in forums, then sticking to a working Blender build with Python 2.7 for about 5 years since I did not want to touch it and break it. My integration actually reversed the embedding process, i.e. instead of using additional modules in the Blender embedded python I embedded Blender in a 3D GIS automation.

Native plugin weirdness aside, Blender Python API is a really powerful tool for creating procedural objects from waves / fluid simulation to astrophysics with amuse.

FreeCAD

FreeCAD is sort of the third part of my physical electrical / mechnical design triumvirate. I occasionally design parts for KiCAD in FreeCAD, or bring multiple boards together to test enclosure fit. FreeCAD also has an extensive python library which is leveraged by KiCAD part library maintainers to parametrically generate parts.

The scripting in FreeCAD can be used much like the PCB layout scripts in KiCAD to create this with circular symmetry, like ball bearings which are difficult and repetitive to do by hand.

Final words

There are lots of other pieces of desktop software I have used that have started shipping with Python API's to address the never ending demand from users to easily automate repeated tasks. The live process for making this blogpost in somewhat recursive fashion can be found here.

Started a new blog post around #python wrapping around a bunch of desktop applications to ease automation / extension. Live updates here as I collate material to flesh it out. pic.twitter.com/zz8b29kHcO

— Tisham Dhar (@whatnick) October 4, 2020

I have even made videos withs a proprietary one, I will live that here for anyone interested in my attempts at a voiceover.

Compiling QGIS in MSVC in 2020

Compiling QGIS on Windows in 200x

I don't quite remember when I decided to help compile QGIS on Windows. It was somewhere between compiling GDAL with ECW support for Photoshop on Windows and getting carried into Direct3D and C# land with NASA WorldWind. It was sometime in the 2000's while still working at Apogee Imaging in Lobethal.

At that point I was manually building a database of the footprints of satellite imagery that filled up a wall cabinet with CD's and DVD's. The technique was something like open up the image, go around edges and trace a polygon. This was days before mature boolean thresholding and reliable/easy raster-to-vector logic.

I hopped on IRC on #qgis in Freenode and chatted with luminaries like timlinux, frankw and gsherman. Listened to the automated notifications from sigq, the commits bot. Things were heating up and instead of a Linux cross-compile to windows using MingW, something native to windows say using MSyS+MingW instead of Cygwin was desired. A lot of GDAL and Qt worked in MingW, so presumably QGIS would too. So I set myself to put together an MSYS environment with all the third-party dependencies that could be used to happily build QGIS. Eventually I built a release in NSIS as well.

My MSYS environment got packed in a zip and shared via FTP/HTTP on a VPS I had back then to the rest of the community. I earned myself a pin in the QGIS core contributor map in Adelaide. Something I am very proud of to this day. Eventually the MingW build got deprecated and native MSVC builds were supported. That's how contributions work, nothing lasts forever. In my IRC days, I helped on-board Nathan Woodrow to QGIS, who in turn I believe helped on-board Nyall Dawson. Nyall has surpassed us all in feature contributions and work on QGIS.

Getting started on QGIS on MSVC blog article. Trying to add some historical perspective on my involvement. Found this acknowledgement in the docs. Thanks to @timlinux . Back in the days of sharing mingw zip files via FTP. pic.twitter.com/NTkQgU5ibN

— Tisham Dhar (@whatnick) August 29, 2020

Fast forward to 2020, compiling QGIS in MSVC

I am getting back into doing lots of Open-source work after long hiatus in private industry with Aerometrex and start-up land with Lorisystems. It is great fun working on mostly in the open at Geoscience Australia. There is actually a recently archived opendatacube + qgis repository here. Seeing that repo and speaking to Nathan and LinuxConfAu inspired me to have a go and getting back into actively working on the Qgis code base. It has sprawled out, with lots and lots of new features. The build system is still familiar via CMake and actually much easier now with MSVC. I cast around for a recent guide and found this. The guide mostly works, however I made some refinements.

• Ditched bison and flex via Cygwin to using the one available via Msys2. These can be found here. Not needing the while Cygwin system helps in keeping the windows build system light. Simply download the binaries and add them to the Osgeo4W binaries directory.
• Captured my CMakeCache.txt to make it easier to reproduce and debug the build environment for others.
• Used Incredibuild in demo mode to use a few NUC's I have lying around to speed up the build. Recording while building failed the first time and worked the next. The whole build from scratch still tooks around 35minutes overall.

I am planning to throw some of my day to day DevOps skills towards the QGIS project and start helping again with Raster enhancements and windows release management. Perhaps getting Incredibuild in the hands of the windows maintainers will help tighten up the iteration cycle and make testing easier.

The twitter thread/ stream of consciousness edition of this is available as well.

Moving from babun to msys2 to get flex and bison required for compiling QGIS from source. https://t.co/W866AOM9Kt pic.twitter.com/fUmqpa9YHY

— Tisham Dhar (@whatnick) June 26, 2020

Writing PhD thesis and living in a hole

I have finally moved house to a crummy student digs to go with the PhD writing mood. Most of my time is spent with WinEdt and latex syntax. I might think of switching allegiance to LyX since Bibus has added Lyx support, I wonder if it will mangle my tex files into LyX specific format.

I have also been doing some TerraSAR-X quad-pol data analysis and comparing decomposition results to dual-pol case. There is a very nice overlap, but some things seem more coherent when the cross-pol scattering is not taken into account - in my case tree trunks standing on water.

I did manage to sneak in some time for open-source and check out the great work Manuel is doing to incorporate Monteverdi support into Qgis. Monteverdi can pull the layers from Qgis open files list and process them. The results currently cannot be passed directly from Monteverdi into Qgis. This issue can be solved by using a custom otbprovider which pushes Monteverdi streams into the QGis view by producing an appropriate QImage.

We have also been wondering whether an application is running inside our outside a NAT, what would be the best way to check this. Say ping an external server outside the NAT and see which source address the request came from, if the source is one particular IP (we have a static IP) then we are inside NAT and need to use internal IP's to connect to certain servers, otherwise we are outside and public IP is fine.

SVM with multiple polygons - it is more fun together

SVM is a classic supervised classifier, but as with all such techniques the output depends on the training set provided. My initial OTB-Qgis SVM used each polygon in a shapefile as a separate training sample and was not ideal for providing extensive training data. The access to vector layer attributes via otb::Datanode makes it feasible to assign multiple polygons the same class value, there is always the fallback to 1 polygon per class if there are no attributes with the polygons. Here are some comparisons with 4 polygons and the results by using 1 polygon per class and all polygons with the same attribute being assigned to 1 class. The 1 polygon per class allows us to distinguish cultivated vegetation vs natural riparian vegetation and 2 types of rocky/bare areas. While the multiple polygons per class aggregates the vegetated areas and bare areas into 2 classes.

Matching things up - SIFT Landmark matching via OTB

Orfeo Toolbox has implemented a few landmark identification techniques - SIFT and SURF. Transforms can be calculated from 2 sets of landmark points using an appropriate model. I had some trouble bringing it to Qgis, the output is just one band. The sample code needs to be extended to work with multi-band images. The in-memory representation of the match images is in double, this can cause array allocation failures. Otherwise this feature matching provides correlation free image matching for images with different dynamics - such as SAR to Optical.

Qgis 0.9 Preview Installer up

I put together an NSIS based installer(long removed) for Qgis 0.9 Preview 1 with some primitive Python detection support for testing, it will complain while loading the Qgis Python bindings if PyQt4-Sip are not located. It should work with the Binary package for PyQt4 available here. I will try to add auto-install of PyQt4 soon.