[QGIS-Developer] Mesh layer

[Vincent Cloarec]

Hi,

With QGIS master you can use updateTriangularMesh.
<https://qgis.org/pyqgis/master/core/QgsMeshLayer.html#qgis.core.QgsMeshLayer.updateTriangularMesh>
Before, there is a workaround that consists to just call createMapRenderer
<https://qgis.org/pyqgis/3.12/core/QgsMeshLayer.html#qgis.core.QgsMeshLayer.createMapRenderer>
without using the renderer.

Vincent

Le sam. 25 avr. 2020 à 11:32, Jorge Almerio <jorgealmerio at yahoo.com.br> a
écrit :

> Hi everyone,
>
> Sometimes I got "NaN" return when trying to get scalar value to a point
> from a Mesh layer. I guess the reason is that it was not rendered
> previously as said in the documentation.
>
> <
> https://qgis.org/api/classQgsMeshLayer.html#a07cb62f04b64979500d3873afb580216
> >
> QgsMeshDatasetValue:
> "Note:
>     It uses previously cached and indexed triangular mesh and so if the
> layer has not been rendered previously (e.g. when used in a script) it
> returns NaN value"
>
> When I turn ON and OFF the loaded mesh layer in the active project it
> Works!
>
> I would like to know if there is a proper way to render the mesh layer,
> before get values.
>
> Below is my code:
>
> proj = QgsProject.instance()
> layerPto = iface.activeLayer() # a Point layer
> layer = proj.mapLayersByName("mesh01")[0] # a Mesh layer
> dataset = QgsMeshDatasetIndex(0,0)
> for feat in layerPto.getSelectedFeatures():
>     ptoGeo = feat.geometry()
>     pt = ptoGeo.asPoint()
>     value = layer.datasetValue(dataset, pt).scalar()
>     print('elevation={}'.format(value))
>
>
>
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