QGIS » QGIS Application

Giovanni Manghi wrote:

For a 1.2gb zipped shapefile I think is safe to say that if you don't limit labelling (by max number of labels, by scale, etc.) is safe to say that is epxected to be slow.

Hi Giovanni,
some clarifications: it's not just slow, we talk about hours (when it does not crash before). And I do not think it's normal, QGIS is able to calculate the centroids of all those geometries in less than 10 seconds if it does not perform the geometry validity check and in my opinion it makes no sense to make a validity check for labeling.

Hi Giovanni,
some clarifications: it's not just slow, we talk about hours (when it does not crash before). And I do not think it's normal, QGIS is able to calculate the centroids of all those geometries in less than 10 seconds if it does not perform the geometry validity check and in my opinion it makes no sense to make a validity check for labeling.

I didn't explained myself very well: what i wanted to say is that I think (I may be wrong) that when the maps has tons of labels then qgis has always been slow (slow is the operation to draw labels, not to compute their position, I think). Have you tried on 2.18?

I didn't explained myself very well: what i wanted to say is that I think (I may be wrong) that when the maps has tons of labels then qgis has always been slow (slow is the operation to draw labels, not to compute their position, I think). Have you tried on 2.18?

Ok, but this is not the case. In fact, the labels to show are only 256 like the geometries. The 256 geometries are multiparts and the parts are a lot (~100,000).

By placing the labels on the perimeter and not around the centroid, everything works perfectly. That's why I say that the problem is due to the calculation of centroids to place the labels and not the rendering of the labels.

On 2.18 there is exactly the same problem.

On 2.18 there is exactly the same problem.

this prove my point, there are no geometry checks in 2.18 (the issue is not the check of geometries, is the drawing of a lot of labels that is historically slow in QGIS).

this prove my point, there are no geometry checks in 2.18 (the issue is not the check of geometries, is the drawing of a lot of labels that is historically slow in QGIS).

You're right on qgis 2.18, and in fact, by testing better, things are a bit different than what I said. Displaying the shapefile labels is slow, but not as much as in series 3 (a few minutes instead of hours), and the centroid algorithm works quickly (as in qgis 3 when the check is disabled).

But the problem for sure is not the drawing of the labels, in fact as written in a previous message, there are only 256 labels and if I create a layer with simple geometries (a point where are the centroids of the 256 geometries), with exactly the same labels of the shapefile at the same location, these labels are shown very quickly.

Mario Baranzini wrote:

this prove my point, there are no geometry checks in 2.18 (the issue is not the check of geometries, is the drawing of a lot of labels that is historically slow in QGIS).

You're right on qgis 2.18, and in fact, by testing better, things are a bit different than what I said. Displaying the shapefile labels is slow, but not as much as in series 3 (a few minutes instead of hours), and the centroid algorithm works quickly (as in qgis 3 when the check is disabled).

But the problem for sure is not the drawing of the labels, in fact as written in a previous message, there are only 256 labels and if I create a layer with simple geometries (a point where are the centroids of the 256 geometries), with exactly the same labels of the shapefile at the same location, these labels are shown very quickly.

ok, so I think we have enough elements to say that this a regression, agree?

ok, so I think we have enough elements to say that this a regression, agree?

Yes, for labeling this is a regression. To display the same labels under the same conditions, it goes from 1 minute and 10 seconds in QGIS 2 to dozens of minutes with 100% cpu in QGIS 3.