Laggy UI with highly detailed watershed

[nicogodet]

We use a 1m MNT and delineated watershed is around 200km² and perimeter around 140km (so more than 140 000 vertices for delineated WS)

Do you use QgsRubberband to draw on canvas ? I had issue with them with polygon with a lot of vertices

[vcloarec]

The watershed is drawn on map canvas using a QgsMapItem derived class under the wood.

I think 140 000 vertices is quite a lot. By the way, I wonder if QGIS handles well such polygon when it is from a vector layer, I never experiment such feature.

But the QgsMapItem drawing is done in the main thread, so that could explain why it is freeze a bit the canvas.

I also wonder if it is not too long to delineate automatically such watershed with this resolution, how many minutes to process?

You are pushing the limit!

[nicogodet]

I know we are pushing the limits :/
We have a lot of small rivers (2 o 3 pixels wide on 1m MNT)

It takes around 25min to delineate when it doesn't crash (I'm still trying to figure out why it crashes)

[vcloarec]

For watershed delineating, maybe you could reduce the resolution, the main stream is not so important, no?

Note, that you can change the raster DEM used to delineate for smaller one, even it is sub watershed.

For crashes, maybe it is due to memory limits, if it does not crash at every time, it is because that will depends on the first extent used to delineate the watershed that is not always the same...

[nicogodet]

Good to know that we can use different resolution for delineation !