QgsMeshLayer class

Represents a mesh layer supporting display of data on structured or unstructured meshes.

Contents

The QgsMeshLayer is instantiated by specifying the name of a data provider, such as mdal, and url defining the specific data set to connect to. The vector layer constructor in turn instantiates a QgsMeshDataProvider subclass corresponding to the provider type, and passes it the url. The data provider connects to the data source.

The QgsMeshLayer provides a common interface to the different data types. It does not yet support editing transactions.

The main data providers supported by QGIS are listed below.

Mesh data providers

Memory data providerType (mesh_memory)

The memory data provider is used to construct in memory data, for example scratch data. There is no inherent persistent storage of the data. The data source uri is constructed. Data can be populated by setMesh(const QString &vertices, const QString &faces), where vertices and faces is comma separated coordinates and connections for mesh. E.g. to create mesh with one quad and one triangle

QString uri(
    "1.0, 2.0 \n" \
    "2.0, 2.0 \n" \
    "3.0, 2.0 \n" \
    "2.0, 3.0 \n" \
    "1.0, 3.0 \n" \
    "---"
    "0, 1, 3, 4 \n" \
    "1, 2, 3 \n"
  );
  QgsMeshLayer *scratchLayer = new QgsMeshLayer(uri, "My Scratch layer", "memory_mesh");

MDAL data provider (mdal)

Accesses data using the MDAL drivers (https://github.com/lutraconsulting/MDAL). The url is the MDAL connection string. QGIS must be built with MDAL support to allow this provider.

QString uri = "test/land.2dm";
QgsMeshLayer *scratchLayer = new QgsMeshLayer(uri, "My Scratch Layer",  "mdal");

Base classes

class QgsMapLayer
Base class for all map layer types.

Public types

struct LayerOptions
Setting options for loading mesh layers.

Constructors, destructors, conversion operators

QgsMeshLayer(const QString& path = QString(), const QString& baseName = QString(), const QString& providerLib = "mesh_memory", const QgsMeshLayer::LayerOptions& options = QgsMeshLayer::LayerOptions()) explicit
Constructor - creates a mesh layer.
QgsMeshLayer(const QgsMeshLayer& rhs) deleted
QgsMeshLayer cannot be copied.

Public functions

auto clone() const -> QgsMeshLayer* override
Returns a new instance equivalent to this one except for the id which is still unique.
auto createMapRenderer(QgsRenderContext& rendererContext) -> QgsMapLayerRenderer* override
Returns new instance of QgsMapLayerRenderer that will be used for rendering of given context.
auto dataProvider() -> QgsMeshDataProvider* override
Returns the layer's data provider, it may be null.
auto dataProvider() const -> const QgsMeshDataProvider* override
Returns the layer's data provider in a const-correct manner, it may be null.
auto datasetValue(const QgsMeshDatasetIndex& index, const QgsPointXY& point) const -> QgsMeshDatasetValue
Interpolates the value on the given point from given dataset.
auto decodedSource(const QString& source, const QString& dataProvider, const QgsReadWriteContext& context) const -> QString override
Called by readLayerXML(), used by derived classes to decode provider's specific data source from project files.
auto encodedSource(const QString& source, const QgsReadWriteContext& context) const -> QString override
Called by writeLayerXML(), used by derived classes to encode provider's specific data source to project files.
auto extent() const -> QgsRectangle override
Returns the extent of the layer.
auto nativeMesh() -> QgsMesh*
Returns native mesh (nullptr before rendering)
auto nativeMesh() const -> const QgsMesh*
Returns native mesh (nullptr before rendering)
auto operator=(QgsMeshLayer const& rhs) -> QgsMeshLayer& deleted
QgsMeshLayer cannot be copied.
auto providerType() const -> QString
Returns the provider type for this layer.
auto readXml(const QDomNode& layer_node, QgsReadWriteContext& context) -> bool override
Called by readLayerXML(), used by children to read state specific to them from project files.
auto rendererCache() -> QgsMeshLayerRendererCache*
Returns native mesh (nullptr before rendering)
auto rendererSettings() const -> QgsMeshRendererSettings
Returns renderer settings.
void setRendererSettings(const QgsMeshRendererSettings& settings)
Sets new renderer settings.
auto triangularMesh() -> QgsTriangularMesh*
Returns triangular mesh (nullptr before rendering)
auto triangularMesh() const -> const QgsTriangularMesh*
Returns triangular mesh (nullptr before rendering)
auto writeXml(QDomNode& layer_node, QDomDocument& document, const QgsReadWriteContext& context) const -> bool override
Called by writeLayerXML(), used by children to write state specific to them to project files.

Signals

void activeScalarDatasetChanged(const QgsMeshDatasetIndex& index)
Emitted when active scalar dataset is changed.
void activeVectorDatasetChanged(const QgsMeshDatasetIndex& index)
Emitted when active vector dataset is changed.

Private functions

auto isReadOnly() const -> bool override
Returns true if the provider is in read-only mode.

Function documentation

QgsMeshLayer::QgsMeshLayer(const QString& path = QString(), const QString& baseName = QString(), const QString& providerLib = "mesh_memory", const QgsMeshLayer::LayerOptions& options = QgsMeshLayer::LayerOptions()) explicit

Constructor - creates a mesh layer.

Parameters
path The path or url of the parameter. Typically this encodes parameters used by the data provider as url query items.
baseName The name used to represent the layer in the legend
providerLib The name of the data provider, e.g., "mesh_memory", "mdal"
options general mesh layer options

The QgsMeshLayer 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.

QgsMeshLayer* QgsMeshLayer::clone() const override

Returns a new instance equivalent to this one except for the id which is still unique.

Returns a new layer instance

QgsMapLayerRenderer* QgsMeshLayer::createMapRenderer(QgsRenderContext& rendererContext) override

Returns new instance of QgsMapLayerRenderer that will be used for rendering of given context.

const QgsMeshDataProvider* QgsMeshLayer::dataProvider() const override

Returns the layer's data provider in a const-correct manner, it may be null.

QgsMeshDatasetValue QgsMeshLayer::datasetValue(const QgsMeshDatasetIndex& index, const QgsPointXY& point) const

Interpolates the value on the given point from given dataset.

Parameters
index dataset index specifying group and dataset to extract value from
point point to query in map coordinates
Returns interpolated value at the point. Returns NaN values for values outside the mesh layer, nodata values and in case triangular mesh was not previously used for rendering

QString QgsMeshLayer::decodedSource(const QString& source, const QString& dataProvider, const QgsReadWriteContext& context) const override

Called by readLayerXML(), used by derived classes to decode provider's specific data source from project files.

Parameters
source data source to decode, typically read from layer's DOM element "datasource"
dataProvider string identification of data provider (e.g. "ogr"), typically read from layer's DOM element
context reading context (e.g. for conversion between relative and absolute paths)
Returns decoded source, typically to be used as the layer's datasource

Typically resolving absolute or relative paths, usernames and passwords or drivers prefixes ("HDF5:")

QString QgsMeshLayer::encodedSource(const QString& source, const QgsReadWriteContext& context) const override

Called by writeLayerXML(), used by derived classes to encode provider's specific data source to project files.

Parameters
source data source to encode, typically QgsMapLayer::source()
context writing context (e.g. for conversion between relative and absolute paths)
Returns encoded source, typically to be written in the DOM element "datasource"

Typically resolving absolute or relative paths, usernames and passwords or drivers prefixes ("HDF5:")

QgsMesh* QgsMeshLayer::nativeMesh()

Returns native mesh (nullptr before rendering)

const QgsMesh* QgsMeshLayer::nativeMesh() const

Returns native mesh (nullptr before rendering)

QgsMeshLayerRendererCache* QgsMeshLayer::rendererCache()

Returns native mesh (nullptr before rendering)

QgsTriangularMesh* QgsMeshLayer::triangularMesh()

Returns triangular mesh (nullptr before rendering)

const QgsTriangularMesh* QgsMeshLayer::triangularMesh() const

Returns triangular mesh (nullptr before rendering)

void QgsMeshLayer::activeScalarDatasetChanged(const QgsMeshDatasetIndex& index) signal

Emitted when active scalar dataset is changed.

void QgsMeshLayer::activeVectorDatasetChanged(const QgsMeshDatasetIndex& index) signal

Emitted when active vector dataset is changed.