Estrarre numero pagine da un PDF

Introduzione

Un utente di QGIS mi contatta e mi chiede come estrarre il numero di pagine di un PDF usando le espressioni di QGIS.

!!! Abstract "Funzione personalizzata" QGIS ha centinaia di espressioni, per quelle che mancano o per crearne di nuove è possibile aggiungere delle funzioni personalizzate usando PyQGIS

Array nel field calc

Introduzione

Il gruppo Array è stato introdotto in QGIS nella prima versione di QGIS 3.0 Girona nel lontano 2018, nella descrizione leggiamo:

!!! Abstract "GRUPPO ARRAY" Nuovo gruppo che contiene funzioni di espressione per la creazione e la manipolazione di array (noti anche come strutture di dati di elenco). L'ordine dei valori all'interno dell'array è importante, contrariamente alla struttura dei dati "mappa", dove l'ordine delle coppie chiave-valore è irrilevante e i valori sono identificati dalle rispettive chiavi.

Impostazioni di progetto influenzano alcune funzioni

Introduzione

Alcune funzioni di QGIS dipendono dalle impostazioni di progetto, questo significa che le stesse funzioni in progetti diversi possono restituire valori diversi. In questo post vedremo le principali funzioni di QGIS da attenzionare.

!!! Abstract "esempio" $area <> area(@geometry)

Come cercare un valore in funzione di un altro

Introduzione

Alcune volte nasce l'esigenza di cercare un valore in una tabella in funzione di un altro valore presente nella stessa tabella, un po' come fa la funzione cerca verticale di Excel, e utilizzarlo in un altro layer.

!!! Abstract "Funzione" La funzione che permette di fare questa magia è la funzione get_feature

HfcQGIS e la sezione Blog

Introduzione

Benvenuti nel nuovo blog di HfcQGIS!

HfcQGIS è la guida al calcolatore di campi di QGIS per la condivisione di conoscenze ed ora ha il suo Blog!!!.

HfcQGIS è un sito web nato nel 2018 da un'idea di Totò Fiandaca e realizzato con la comunità OpenDataSicilia, un particolare grazie va a Giovan Battista Vitrano che mantiene sempre aggiornato il tema del sito alle ultime novità. L'obiettivo iniziale del sito era quello di fornire una guida completa al calcolatore di campi, un potente strumento che consente di eseguire calcoli sui dati geografici.

Negli anni, HfcQGIS si è evoluto in una piattaforma di condivisione di contenuti per la comunità QGIS. Il sito offre ora una serie di risorse, tra cui:

Years ago, the QField community and its users showed their love for their favourite field app by supporting a successful crowdfunding to improve camera handling.

Since then, OPENGIS.ch has continued to lead the development of QField with the regular support of sponsors. We couldn’t be prouder of the progress we have made, with plenty of new features added in every major release. This includes major improvements to positioning including location tracking, integration of external GNSS receivers through not only Bluetooth but TCP/UDP and serial port connections, accuracy indicator and constraints, and most recently sensors reading to list a few.

We are now calling for the community to help further better QField and unlock an important milestone: background location tracking service.

Pledge now

Main goal: background location tracking on Android – 25'000€

Currently, QField requires users to keep their devices’ screen on and have the app in the foreground to keep track of the device’s positioning location. On mobile devices, this can drain batteries faster than many would want to, in environments where charging options are limited.

This crowdfunding aims at removing this constraint and allow QField - via a background service - to constantly keep tracking location even while the device is suspended (i.e., when the screen is turned off / locked).

To achieve this, a significant amount of work is required as the positioning framework on Android will need to be relocated to a dedicated background service. Recent work we’ve done adding a background service to synchronize captured image attachments in QFieldCloud projects armed us with the assurances that we can achieve our goal while giving us an appreciation of the large amount of work needed.

Some of the benefits

Running out of battery is the nightmare of most field surveyors. By moving location tracking to a background service, users will be able to improve their battery life considerably and keep focusing on their tasks even if it involves switching to a different app.

Furthermore, while OPENGIS.ch ninjas remain busy squashing reported QField crashes all year long, there will always be unexpected scenarios leading to abrupt app shutdowns, such as third-party apps, systems running out of battery, etc. To address this, the background service framework will also act as a safeguard to avoid location data loss when QField unexpectedly shuts down and offer users means to recover that data upon re-opening QField.

Stretch goal 1: background navigation audio feedback 5'000€

The second stretch goal builds onto QField’s nice fly-to-point navigation system. If the QField community meets this threshold, a new background navigation audio feedback informing users in the field of their proximity to their target will be implemented.

The audio feedback will use text-to-speech technology to state the distance to target in meters for a given time or distance interval.

Stretch goal 2: iOS 15'000€

The main goal will cover the Android implementation only. Due to being a very low level work we will have to replicate the work for each platform we support. If we reach stretch goal 2 we will also implement this for iOS.

Pledge now:

In case you do not see the embedded form you can open it directly here .

Thanks for supporting our crowdfunding and keep an eye on our blog for updates on the status.

The latest version of QField is out, featuring as its main new feature sensor handling alongside the usual round of user experience and stability improvements. We simply can’t wait to see the sensor uses you will come up with!

The main highlight: sensors

QField 2.8 ships with out-of-the-box handling of external sensor streams over TCP, UDP, and serial port. The functionality allows for data captured through instruments – such as geiger counter, decibel sensor, CO detector, etc. - to be visualized and manipulated within QField itself.

Things get really interesting when sensor data is utilized as default values alongside positioning during the digitizing of features. You are always one tap away from adding a point locked onto your current position with spatially paired sensor readings saved as point attribute(s).

Not wowed yet? Try pairing sensor readings with QField’s tracking capability! ;) Head over QField’s documentation on this as well as QGIS’ section on sensor management to know more.

The development of this feature involved the addition of a sensor framework in upstream QGIS which will be available by the end of this coming June as part of the 3.32 release. This is a great example of the synergy between QField and its big brother QGIS, whereas development of new functionality often benefits the broader QGIS community. Big thanks to Sevenson Environmental Services for sponsoring this exciting capability.

Notable improvements

A couple of refinements during this development cycle are worth mentioning. If you ever wished for QField to directly open a selected project or reloading the last session on app launch, you’ll be happy to know this is now possible.

For heavy users of value relations in their feature forms, QField is now a tiny bit more clever when displaying string searches against long lists, placing hits that begin with the matched string first as well as visually highlighting matches within the result list itself.

Finally, feature lists throughout QField are now sorted. By default, it will sort by the display field or expression defined for each vector layer, unless an advanced sorting has been defined in a given vector layer’s attribute table. It makes browsing through lists feel that much more natural.

A brand new version of QField has been released, packed with features that will make you fall in love with this essential open source tool all over again with a focus on capturing more while you are in the field. QField 2.7 nicknamed “Heroic Hedgehog” also includes a number of worthy fixes making it a crucial update to get.

New recording capabilities

The highlight of QField 2.7 is the new audio and video recording capability straight from the feature form. In addition to preexisting still photo capture, this functionality allows for video motion and audio clips to be added as attachments to feature attributes.

The audio recording capability can come in handy in the field when typing on a keyboard-less device can be challenging. Simply record an audio note of observations to process later.

The experience wouldn’t be complete without audio and video playback support, which we took care of in this version too. Playback of such media content within the feature form gives an immediate feedback and saves time. For those interested in full screen immersion, simply click on the video frame to open the attached in your favorite media player. We also took the opportunity to implement audio and video playback on QGIS so people can easily consume the fruits of their labor in the field at their workstation.

We would be remiss if we didn’t mention map canvas rotation functionality added in this version. This is a long-requested functionality which we are happy to have packed into QField now. Pro-tip: when positioning is enabled, double tapping on the lower-left positioning button will have the map canvas follow both the device’s current location as well as the compass orientation.

Finally - some would argue “most importantly” ;) - QField is now equipped with a beautiful dark theme which users can activate in the settings panel. By default on Android and iOS, QField will follow the system’s dark theme setting. In addition to the new color scheme, users can also adjust the user interface font size.

Big thanks to Deutsches Archäologisches Institut who funded the majority of the new features in this release cycle. Their investment in making QField the perfect tool for them has benefited the community as a whole.

A ton of bug fixing across all platforms

Important stability improvements and fixes to serious issues are also part of this release. Noteworthy fixes include WFS layer support on iOS, much better Bluetooth connectivity on Android, and vertical grid improvement on Windows.

For users facing reliability issues with the native camera on Android, we have spent time supersizing the camera we ship within QField itself. During this development cycle, it has gained zoom and flash controls, as well as a ton of usability improvements, including geo-tagging.

To know more about this release, read the full change log on QField’s github release page .

It’s only been a few weeks into the new year, but we’ve got great news for you: a brand new QField 2.6 “Geeky Gecko ?” has been released with a focus on positioning improvements, including Bluetooth support for Windows. And with that, we are delighted to remove the ‘beta’ status from QField for Windows.

New positioning features

Let’s open with a bang: QField 2.6 now supports NMEA streaming from external GNSS devices over TCP, UDP, and serial ports, in addition to preexisting Bluetooth connectivity. This new functionality means that QField is now compatible with a much larger range of GNSS devices out there.

These new receivers unlock NTRIP-driven centimetre accuracy for devices that use the Bluetooth connection to a manufacturer’s application to connect to NTRIP servers. In this scenario, QField could not initiate a Bluetooth connection since it was already taken. With the new TCP and UDP receivers - provided the manufacturer’s application offers NMEA streaming over either of those Internet protocols - QField can connect and consume high-accuracy positioning.

The presence of a serial port receiver provides support for external GNSS devices using Bluetooth on Windows via the virtual serial port created by the operating system. The lack of Bluetooth support on Windows was a long-wanted enhancement from QField users on that platform and was the last blocker for the ‘beta’ status to go away.

In addition, QField 2.6 allows users to pick from half a dozen metrics a value to attach to the measure (M) dimension of geometries being digitized when locked to the current position. This functionality is available to both users digitizing and the positioning tracker. The measurement values available as of 2.6 are timestamp, ground speed, bearing, horizontal accuracy and vertical accuracy, as well as PDOP, HDOP and VDOP values.

Growing Continuous Integration (CI) testing framework now covers positioning

Starting with version 2.6, QField ships with increased quality assurances thanks to the addition of tests covering positioning functionalities in its growing CI framework.

Practically speaking, this means that every single line of QField code changed is now being tested against positioning-related regression, significantly decreasing the risks of shipping a new version of QField with broken functionality in the area of antenna height, vertical grid shift, and ellipsoidal height adjustments.

We would like to commend Deutsche Bahn for funding the required work here. This could not have come in soon enough as more and more people are opting for QField and relying on it for their crucial day-to-day fieldwork.