How to make QGIS layer update from changed data source?

How to make QGIS layer update from changed data source?

Or maybe I did something two minutes ago. The one reproducible way of getting it to update is to duplicate the layer from the legend menu – the duplicate always gets its data from the current shapefile, and the original layer updates itself too! So there must be some way of doing it.

What are the different types of layers in QGIS?

layers as a result of an SQL-like query based on one or many layers: the virtual layer. QGIS also provides tools to import/export different formats. QGIS allows you to create new Shapefile layers, new SpatiaLite layers, new GPX layers and new Temporary Scratch layers. Creation of a new GRASS layer is supported within the GRASS plugin.

How to copy features from one layer to another?

If you’ll follow the screenshots below you’ll be able to copy / cut features from one layer and to paste / move them to another layer: This is how the first layer looks: Going back to the first layer and selecting some features: Select Copy or Cut from the Edit menu if you want to duplicate or move existing features into another layer:

Is it possible to reopen a file before QGIS 2.10?

Before QGIS 2.10, a file was reopened on every single access (e.g. repaint). Since QGIS 2.10 the file handle is kept open and this means if a file is replaced the handle still points to the old file on Unix based systems. Unfortunately there is no API to nicely force QGIS to reopen the file in QGIS 2.10. As a workaround you can use an ugly hack:

Can you open a GeoJSON file in QGIS?

QGIS can natively open geojson file but it doesn’t always consistently work – at least for me, and I’m not sure why it works sometimes or doesn’t. You can try doing one of the following options below to add geojson to QGIS for viewing.

How to save a leaflet in QGIS for Ubuntu?

In QGIS for UBUNTU hit CTRL-SHIFT-N (which wasn’t working on my machine) or use the path Layer->New->New Shapefile Layer. We will see a dialog similar to this: I saved it under the name roads.shp.

How to add a GeoJSON Fiel to a file?

I’ve tried all 3 different file extensions and they all seem to work. You can also add geojson fiel via a web service URL or a local networked drive. Just click the Open Data Source Manager button >> Vector Data >> Protocol HTTP (S), cloud, etc. >> Select GeoJSON type >> URI path >> Add.

How to create a polygon layer in QGIS using Python?

QGIS will prompt you to choose one. The syntax is similar if you want to create a line or a polygon layer. A line is created with two points: and a polygon is created with a list of points: With these premises, a line is created as follows: A polygon is created as follows:

How is a point memory layer created in QGIS?

A point is created as follows: We have just created a point memory layer, defined by a specific Coordinate Reference System (in this case, ESPG:4326). Without this declaration:

How to force QGIS to reopen a file?

Unfortunately there is no API to nicely force QGIS to reopen the file in QGIS 2.10. As a workaround you can use an ugly hack: I just introduced a new method which will be available starting from QGIS 2.12:

Is there way to source shapefile to layer file in QGIS?

Is there a way to source a shapefile to a layer file in QGIS much like how you do this in the properties of an ArcGIS layer? (i.e. Go to layer properties, source tab and then just depress the ‘Set Dat Source’ button) I’ve been all over the layer properties in QGIS and I don’t see this anywhere…

Is the picklayer plugin included in QGIS 2.10?

The feature has been included in PickLayer plugin that allows to perform actions on clicked layer and feature From release 2.10 QGis Api include QgsVectorLayer::setDataSource method:

What happens if somebody edits the same feature in QGIS?

This version of QGIS does not track if somebody else is editing the same feature at the same time as you are. The last person to save its edits wins. For an optimal and accurate edit of the vector layer geometries, we need to set an appropriate value of snapping tolerance and search radius for features vertices.

Do you have to digitize all vertices for QGIS to work?

The advantage is that you don’t have to digitize all vertices of the common boundary. If the new geometry is totally covered by existing ones, it gets cleared and the new feature will have no geometry when allowed by the provider, otherwise saving modifications will make QGIS pop-up an error message.

How to draw country polygons in QGIS 4.5?

Here we create an object of the QgsGraduatedSymbolRenderer class that we want to use to draw the country polygons from our layer using a graduated color approach based on the population attribute ‘POP2005’. The name of the field to use is set via the renderer’s setClassAttribute () method in line 2.

How to create a new GeoPackage layer in QGIS?

QGIS will automatically add the new layer to the legend, and you can edit it in the same way as described in section Digitizing an existing layer. Further management of SpatiaLite layers can be done with the DB Manager. See DB Manager Plugin. To create a new GeoPackage layer go to Layer ‣ New ‣ New GeoPackage Layer… .

What happens to temporary scratch layers in QGIS?

Temporary Scratch Layers are in-memory layers, meaning that they are not saved on disk and will be discarded when QGIS is closed. They can be handy to store features you temporarily need or as intermediate layers during geoprocessing operations.

Is there any way to get QGIS to identify different shapes?

And they are of different shapes: square, rectangle, circle and polygonal. Is there any way I can get QGIS (or any tool for that matter) to identify using the image different shapes (the borders are very visible) and create the shape for me? The image has clear border, all I want is shape layer above it.

How to create a new layer in pyqgis?

Previously, we created layers by loaded existing datasets into our project. In this example, we will create a new layer from scratch. To get started, let’s create a new QgsVectorLayer object for point geometries with the layer name “temp” and a memory data provider:

How is the qgsvectorlayer constructed in QGIS?

The QgsVectorLayer is constructed by instantiating a data provider. The provider interprets the supplied path (url) of the data source to connect to and access the data. path ( str = ”) – The path or url of the parameter.

When do you call addattribute in pyqgis?

Calls to addAttribute () are only valid for layers in which edits have been enabled by a call to startEditing (). Changes made to features using this method are not committed to the underlying data provider until a commitChanges () call is made. Any uncommitted changes can be discarded by calling rollBack ().

How to create a new SpatiaLite layer in QGIS?

To create a new SpatiaLite layer for editing, choose New ‣ New SpatiaLite Layer… from the Layer menu. The New SpatiaLite Layer dialog will be displayed as shown in Figure_create_spatialite. The first step is to select an existing SpatiaLite database or to create a new SpatiaLite database.

How does the vector Layer constructor work in QGIS?

The vector layer constructor in turn instantiates a QgsVectorDataProvider subclass corresponding to the provider type, and passes it the url. The data provider connects to the data source.

How to create line with three points with Python in QGIS?

Creating line with three points with Python in QGIS? I’m new to Python and I’m having some dificulties. I want to create a simple layer with a line in the console of QGIS with Python. How can I do that? Thanks for contributing an answer to Geographic Information Systems Stack Exchange! Please be sure to answer the question.

Why is my QGIS plugin not updating features?

Using the temporary fids given to the pre-commit features prevented making the changes to the other tables, which needed to reference them. Also, this method caused QGIS to crash/segmentation fault if the Undo command was used (on Linux, and with Undo, Redo on Windows). Is this a bug, or am I just approaching this in the wrong way?

Why does layer.isvalid ( ) always return false?

Whenever I run it, layer.isValid () always returns False (or “Layer is not valid!” in this case). I’m not sure what I am doing wrong here, or if I have instantiated the QgsVectorLayer variable incorrectly.

How are colors represented in QGIS vector layer?

QGIS uses the standard QtGui.QColor object for representing colors. See the QColor class reference for more information. A new QColor object can be created using a color name (e.g. magenta ), a color hex value (e.g. #ff00ff) or RGB values (e.g. 255, 0, 255 ):

How to add a plugin to QGIS Repo?

How to add your plugin to this repository. Go to QGIS plugin repo and click on Share a plugin. The approval procedure should take 2 weeks maximum. If not approved, a e-mail will be sent to you.

How are symbols created in the QGIS programming language?

In QGIS, a symbol is a container for symbol layers. Each symbol layer contributes to the overall appearance of a symbol. For example, a polygon with a grey fill and red hatched lines is created using two layers: a grey fill layer and a red line pattern layer.

How is the map canvas implemented in QGIS?

Map canvas is implemented as QgsMapCanvas class in qgis.gui module. The implementation is based on the Qt Graphics View framework. This framework generally provides a surface and a view where custom graphics items are placed and user can interact with them.

Which is the most important widget in QGIS?

The Map canvas widget is probably the most important widget within QGIS because it shows the map composed from overlaid map layers and allows interaction with the map and layers. The canvas shows always a part of the map defined by the current canvas extent.

How can I embed QGIS in a window?

It can be also embedded into an existing widget or window. When using .ui files and Qt Designer, place a QWidget on the form and promote it to a new class: set QgsMapCanvas as class name and set qgis.gui as header file. The pyuic4 utility will take care of it. This is a very convenient way of embedding the canvas.