Hi Adam,
You are correct in your assertions here. You will need to tune the simplify
value for your data so that any slivers/distortion are acceptable to the eye.
It defaults to 1.0, which is quite aggressive, so you will generally want to
set this value yourself. Just bear in mind that reducing/removing
simplification (as you mention, setting to 0 will remove it entirely) will
increase the size of your tiles and result in greater network latency when
loading tiles, so you will need to weigh both sides (presentation &
performance) of this compromise as they both impact the overall UX.
You are also correct that you could create another table or view that shows
just the outlines of your polygons. You could also do this directly in your
tileserver SQL; here’s an example using the PostGIS function "ST_ExteriorRing”
and Arches's "mv_geojson_geoms” view:
SELECT resourceinstanceid::text,
false AS poly_outline,
(row_number() over ())::text as __id__,
geom AS __geometry__
FROM mv_geojson_geoms
WHERE ST_GeometryType(geom) = 'ST_Polygon'
UNION
SELECT resourceinstanceid::text,
true AS poly_outline,
(row_number() over ())::text||'-outline' as __id__,
ST_ExteriorRing(geom) AS __geometry__
FROM mv_geojson_geoms
WHERE ST_GeometryType(geom) = 'ST_Polygon';
Then you can use filters in your mapbox styles to paint the outlines and fills
based on the “poly_outline” property. Bear in mind, that this approach
sacrifices additional server overhead (due to the spatial processing to create
the exterior rings, primarily) in an attempt to reduce the data volume in your
tiles. This may, however, backfire depending on the size of your geometries
relative to the zoom levels users will commonly view them at. ie you will be
able to clip your geometries, but each tile will include duplicated coordinate
values for every vertex. If duplicating vertices generates more coordinates
per tile than turning clipping off then this approach could both increase
server overhead and tile data size.
Of course, which solution is best depends on your data, application and use
cases. I would encourage anyone to use some trial & error to determine what
will work best for a particular context. You can use the admin UI to modify
your tileserver configurations, which is a nice way to try things out w/o
having to use SQL to update records directly.
Also, you should always consider using caching, but be aware that you’ll need
to manage your own caches (for example, creating scheduled jobs to
truncate/reseed, if needed).
- Rob
> On Jan 29, 2018, at 10:30 AM, Adam Cox <[email protected]> wrote:
>
> Hey Rob, this worked great! Thanks for the quick response.
>
> One other thing I'm noticing is that the generalizing that there seems to be
> a default, non-zero value for "simplify"... I removed that parameter because
> simplifying adjacent polygons created gaps at some zoom levels. However, it
> wasn't until I explicitly set "simplify":0 that it actually rendered without
> any simplification. Ultimately, it would probably be best to make a separate
> postgis that has the outlines as lines, not polygons, and add that into the
> mix.
>
> Adam
>
> On Mon, Jan 29, 2018 at 12:20 PM, Rob Gaston <[email protected]
> <mailto:[email protected]>> wrote:
> Hi Adam,
>
> You should be able to handle this by using the “clip” parameter for the
> VecTiles provider (see here:
> http://tilestache.org/doc/TileStache.Goodies.VecTiles.server.html
> <http://tilestache.org/doc/TileStache.Goodies.VecTiles.server.html>).
>
> Here’s a quick example using the “rivers.json” file, note the “clip”
> parameter included in the provider definition:
> {
> "type": "vector",
> "layers": [{
> "id": "rivers",
> "type": "line",
> "source": "rivers",
> "source-layer": "rivers",
> "layout": {
> "visibility": "visible"
> },
> "paint": {
> "line-width": 2,
> "line-color": "rgb(37, 58, 241)"
> }
> }],
> "config": {
> "provider": {
> "class": "TileStache.Goodies.VecTiles:Provider",
> "kwargs": {
> "dbinfo": {
> "host": "localhost",
> "user": "postgres",
> "password": "postgis",
> "database": "arches",
> "port": "5432"
> },
> "simplify": 0.5,
> “clip": false,
> "queries": [
> "select gid as __id__, name,
> st_asgeojson(geom) as geojson, st_transform(geom, 900913) as __geometry__
> from rivers"
> ]
> }
> },
> "allowed origin": "*",
> "compress": true,
> "write cache": false
> }
> }
>
>
> You should note: in some cases (depending on the resolution and size of your
> geometries) turning off clipping may impact performance as the entire
> geometry will be included in your tiles. I think that turning clipping off
> is really only useful for layers where you need a polygon outline style. I
> would imagine that in most cases the performance impact of this can be
> mitigated by tuning your simplification and cache parameters.
>
> - Rob
>
>
>
>> On Jan 29, 2018, at 9:46 AM, Adam Cox <[email protected]
>> <mailto:[email protected]>> wrote:
>>
>> While trying to add a new tileserver layer to my Arches 4.0.1 installation,
>> I came across a rendering issue that I'm wondering if anyone else has dealt
>> with. My layer is a postgis table of polygons, and in QGIS it shows up just
>> fine (these are boundaries of multi-county regions in Florida). However,
>> when I make a tileserver layer in Arches from it, I get the following
>> result, which has an extra perpendicular grid that is non-existent in the
>> dataset.
>>
>>
>> <https://lh3.googleusercontent.com/-lrfenYtfbMs/Wm9cUm_glfI/AAAAAAAAB0A/FXMvWrQ54p8TlyR2Xv7DgeOpJDPTe1gqQCLcBGAs/s1600/tileserver%2Bissue.png>
>> From the way this grid shows up (variably at different zoom levels, etc.), I
>> can tell it's an outline of the actual tiles themselves. Does anyone know
>> how to fix this? In the Arches Map Layer manager, I have the following for
>> the Service Styling:
>>
>> [
>> {
>> "layout": {
>> "visibility": "visible"
>> },
>> "paint": {
>> "fill-color": "#343434"
>> },
>> "source": "FPAN Regions",
>> "source-layer": "FPAN Regions",
>> "type": "fill",
>> "id": "fpan_region"
>> },
>> {
>> "layout": {
>> "visibility": "visible"
>> },
>> "paint": {
>> "line-color": "#ee0000",
>> "line-width": 2
>> },
>> "source": "FPAN Regions",
>> "source-layer": "FPAN Regions",
>> "type": "line",
>> "id": "fpan_region-outline"
>> }
>> ]
>>
>> Thanks!
>> Adam
>>
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