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When a canvas changes its extent a extentsChanged signal is emitted. When you connect this signal to a method (called slot), then you are able to run this method whenever the extent changes. To deploy this mechanism I altered your code in the following way. # Declare a global variable to hold the reference to QGIS canvas canv = None # here comes your ...


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To add to Joseph's list of suggested speedups, you can alter the refresh interval of the canvas (by default it's a four times a second, 250ms, but you can make this value larger, say 1000 ms). This might speed up total elapsed time by reducing the number of canvas repaints (the rendering will still be happening in background threads). I'd need to write ...


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As an alternative, if you want to speed up rendering then you could try the following instead of playing with the rendering order: For Rasters Create a virtual raster(s) from multiple raster layers by going to the menubar: Raster > Miscellaneous > Build Virtual Raster (Catalog) For Vectors Create a memory layer(s) from multiple vector ...



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