Revised text size for lakes

[Ircama]

Revised text size for lakes

[Edited summary]

This PR proposes to scale up the font size for large water area labels (natural=water or landuse=reservoir/basin) used for lakes (currently they are all rendered with a fixed font size, using text-size: 12).

It supersedes and attempts to improve unmerged PRs #2139 and #2287 for the specific relation to the text size used for water areas.

[imagico]

I am not so familiar with the Mapnik label placement parameters - do these here assure that the center points of offset labels are still within the polygon area?

In general with the way_pixels limits it would IMO make sense to further relax the zoom limits, i.e. allow labels for sufficiently large lakes already from z8/z7, maybe with a somewhat raised lower way_pixels limit.

[pnorman]

This would be our first use of text-placements so it'll need more testing than normal to make sure it's not cut off at MT edges.

[matthijsmelissen]

@Ircama The text-wrap-width would also need to increase with increasing font-size.

Everything else looks fine to me.

@pnorman How are we going to test that? We have seen quite different behaviour on production and on development servers in this respect.

[pnorman]

@pnorman How are we going to test that? We have seen quite different behaviour on production and on development servers in this respect.

Kosmtik/TM tends to be worse for metatile issues because it has smaller metatiles. If we don't see too many issues in development it should be fine in production. But this will need testing on Mapnik 2.2 and Mapnik 3.0.

[Ircama]

@math1985

@Ircama The text-wrap-width would also need to increase with increasing font-size.

OK I'll revise this parameter and perform tests.

@imagico

In general with the way_pixels limits it would IMO make sense to further relax the zoom limits,

I think that currently no text is shown for lakes with zoom < 10.

Surely big lakes like the Great Lakes in North America (as well as Caspian Sea, Black Sea, etc.) need to be managed but would be better with some specific PR.

[pnorman]

Can you change the text size logic so it's the same as landcover? See https://github.com/gravitystorm/openstreetmap-carto/blob/master/amenity-points.mss#L1455-L1475 for an example

e.g.

    [zoom >= 9][way_pixels > 3000],
    [zoom >= 17] {
      text-name: "[name]";
      text-size: @landcover-font-size;
      text-wrap-width: @landcover-wrap-width-size;
      [way_pixels > 12000] {
        text-size: @landcover-font-size-big;
        text-wrap-width: @landcover-wrap-width-size-big;
      }
      [way_pixels > 48000] {
        text-size: @landcover-font-size-bigger;
        text-wrap-width: @landcover-wrap-width-size-bigger;
      }
      text-fill: darken(@danger_area, 40%);
      text-face-name: @bold-fonts;
      text-halo-radius: @standard-halo-radius;
      text-halo-fill: @standard-halo-fill;
      text-placement: interior;
    }

I'm not finding many MT issues, but I did find one in Kelowna

z10

z11

z12

z13

This needs more investigation, but I'll do that after the way_pixel MSS changes.

It is also disconcerting to see the text size shrink as you zoom in.

[Ircama]

@pnorman: thanks for your review; I'll certainly compare landcover logic through a new update.

[Ircama]

It is also disconcerting to see the text size shrink as you zoom in.

Already discussed here:
#2287 (comment)

The idea of considering shrinking text size was to avoid of not showing the text at certain zooms in case of limited space. Anyway, if this is not considered appropriate, I'll remove the text-placements logic.

[Ircama]

Code revised so that the text size logic is similar to the landcover example in amenity-points.mss.
Kept 6 levels of way_pixels where two of them are the same as the landcover example in amenity-points.mss.
Removed the text-placements logic.

Sample images with some lake sizes at different zooms:

Zoom 9

Zoom 10

Zoom 11

Zoom 12

Zoom 13

Zoom 14

Zoom 15

Zoom 16

Note: I used Kosmtik for testing (and found important rendering differences between Tilemill for Windows due to the very different Mapnik versions)

[pnorman]

Code revised so that the text size logic is similar to the landcover example in amenity-points.mss.

Is there a reason to not use the exact way_pixel thresholds and values for text-size and text-wrap-width?

[pnorman]

ah, one potential reason is landcover starts at 10px and water at 12. Still, I'd prefer to reuse thresholds and variables when possible.

[Ircama]

ah, one potential reason is landcover starts at 10px and water at 12. Still, I'd prefer to reuse thresholds and variables when possible.

Progression used in amenity-points.mss:

• default font size 10, wrap 25
• for way_pixels > 12000: font size 12, wrap 35
• for way_pixels > 48000: font size 15, wrap 45

Settings previously used for water rendering:

• fixed font size 12, wrap 30

What I did by now was the following:

• The default is the same as what used in amenity-points.mss (font size 10, wrap 25)
• for way_pixels > 4000: font size 10->12, wrap 25->30 (the current default)

All next progressions have increased size for a better representation (as far as it looked to me):

• for way_pixels > 12000: font size 12->15, wrap 35
• for way_pixels > 48000: font size 15->17, wrap 45
• for way_pixels > 1000000: font size 15->22, wrap 45->150
• for way_pixels > 1500000: font size 15->27, wrap 45->150

There is no particular difference for zooms <=13, but for zooms 14+ the result looks better.

Anyway, I will provide a new commit with the exact logic of amenity-points.mss as well as similar samples to allow comparison.

[Ircama]

The code has been revised in this second commit, so that the text size logic is exactly the same as landcover in order to allow comparison with the rendering from the first commit.

The following images IMHO would confirm that for zooms 14+ the result of the first commit looks better especially for bigger lakes.

Images show exactly the same zones of the previous commit (FYI, z9 has been left out as no text is shown).

Zoom 10:

Zoom 11:

Zoom 12:

Zoom 13:

Zoom 14:

Zoom 15:

Zoom 16:

[imagico]

For islands labeling is capped at 800k pixels - it might make sense to do the same for lakes.

[Ircama]

For islands labeling is capped at 800k pixels - it might make sense to do the same for lakes.

Considering that generally the center of a lake should not be too crowded of data (while an island can host a city), there should be no particular prevention to adopt a bigger font size at high zoom level.

In the testing pictures shown above there are four lakes: Lago di Como (biggest), Lago d'Iseo, Lago di Endine, Lago d'Idro.

Here are their way_pixels at different zooms:

Lago di Como (large):

zoom	way_pixels
z10	12878,1
z11	51512,2
z12	206049
z13	824191
z14	3296780
z15	13187100
z16	52748300
z17	210993000

Lago d'Iseo (medium):

zoom	way_pixels
z10	5382,31
z11	-
z12	86116,9
z13	344466
z14	1377870
z15	5511490
z16	22045900
z17	88183400

Lago di Endine (small):

zoom	way_pixels
z12	3029,61
z13	not shown
z14	48473.7
z15	193895
z16	775578
z17	3102310

Lago d'Idro (small):

zoom	way_pixels
z10	not shown
z11	3854,84
z12	-
z13	-
z14	246680
z15	986764
z16	3947040
z17	15788200

By capping way_pixels to 800000, you do not see "Lago di Como" at z13.
You do not see Lago d'Iseo at z14. Lago di Idro will be shown until zoom = 14.
Lago di Endine will not be shown at z16.

I would suggest reconsidering my first commit.

[matthijsmelissen]

Thanks!