On Fri, 18 Feb 2022 at 02:22, C Hamilton <adenacult...@gmail.com> wrote: > > I am thinking of adding an algorithm that automates the creation of a density > heat map of a point vector layer by the following steps. > 1. Call the "Create grid" algorithm. > 2. Call the "Count points in polygon" algorithm. > 3. Style it with "Graduated" style and choose a gradient from a selection of > heatmaps. This would need to be able to automatically scale to the min and > max values and allow the user to select the mode. > > All except for the last can be easily modeled in QGIS; however, there is no > color ramp QgsProcessingParameter for a heatmap.Is there a way to use > QgsProcessingParameterEnum to display a gradient image. Is there a QGIS API > call that would retrieve a set of gradients that could be added to the > QgsProcessingParameterEnum?
My approach would be: 1. Get a list of all color ramp names via QgsStyle.defaultStyle().colorRampNames() 2. Use a QgsProcessingParameterString parameter for the color ramp name instead of a QgsProcessingParameterEnum, and use the approach described at https://qgis.org/pyqgis/master/core/QgsProcessingParameterString.html#qgis.core.QgsProcessingParameterString to show the parameter as a combobox containing only the existing color ramp names. i.e. ramp_names = QgsStyle.defaultStyle().colorRampNames() ramp_name_param = QgsProcessingParameterString('RAMP_NAME', 'Color ramp name') ramp_name_param.setMetadata( {'widget_wrapper': {'value_hints': ramp_names } } ) self.addParameter(ramp_name_param) Why use a string parameter instead of an enum? Well, the enum parameters are designed for a fixed set of choices which are internally all referred to by their numerical index. It works well for choices which are static, and which won't ever vary installation-by-installation. But color ramps WILL vary install by install, as users may have renamed/added/removed ramps. So the numerical indexes of different ramps won't necessarily match across different installs. Ultimately, if another script/process/model uses your algorithm and has a hard coded value for this parameter, of say "5", corresponding to a desired color ramp on the developers machine, then different users will get totally different ramps corresponding to this value! With the string approach the parameter value would always be hardcoded as a string value (the ramp name), so things remain nice and predictable across different installations*. Nyall * of course, a user may still have deleted the desired color ramp, so you should put a run-time check in your processAlgorithm step to test whether the parameter value for RAMP_NAME is actually available in the default style. Something like: ramp_name = self.parameterAsString(parameters, 'RAMP_NAME', context) ramp = QgsStyle.defaultStyle().colorRamp(ramp_name) if ramp is None: raise QgsProcessingException('Color ramp {} is not available'.format(ramp_name)) > > Any ideas would be appreciated. This can be manually done in 3 steps by > separately running each of the algorithms and then styling the resulting > vector layer, but it would be nice if it could be done with one algorithm. > > Thanks!!! > > Calvin > _______________________________________________ > QGIS-Developer mailing list > QGIS-Developer@lists.osgeo.org > List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer _______________________________________________ QGIS-Developer mailing list QGIS-Developer@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
