wipfli

Vector Landcover Notes

I would like to be able to make myself one day a vector landcover tileset that looks as good as the ones of the large consumer maps. I tried doing this a bit but so far I have not found a good solution.

The landcover should give you an idea how the nature looks like in a place, whatever that means...

In this gist I would like to write down some notes around the challenges of making a vector landcover tileset.

Related to onthegomap/planetiler#550

dschep

CREATE OR REPLACE FUNCTION ST_LineChunk(geom geometry, max_length float8) RETURNS SETOF geometry AS $$
WITH
  points AS (
    SELECT generate_series(0, CEIL(ST_Length(geom) / max_length)::int)
      / CEIL(ST_Length(geom) / max_length) "end"
  ),
  line_points AS (SELECT LAG("end", 1) OVER (ORDER BY "end") "start", "end" FROM points)
SELECT ST_LineSubstring(geom, "start", "end")
FROM line_points
WHERE "start" IS NOT NULL AND "start" <> 1

dschep

--  ported from https://github.com/pramsey/minimal-mvt/blob/58f3e695a305f42024dcf0ba395590bf39b0b573/minimal-mvt.py#L63-L81
CREATE OR REPLACE FUNCTION ST_TileEnvelope(tileZoom integer, tileX integer, tileY integer) RETURNS geometry AS $$
-- Width of world in EPSG:3857
DECLARE	worldMercMax float = 20037508.3427892;
DECLARE worldMercMin float = -1 * worldMercMax;
DECLARE worldMercSize float = worldMercMax - worldMercMin;
-- Width in tiles
DECLARE worldTileSize float = power(2, tileZoom);
-- Tile width in EPSG:3857
DECLARE tileMercSize float = worldMercSize / worldTileSize;

dschep

import { useState } from "react";

const useLocalStorageState = (storageKey, defaultValue) => {
  const [value, setValue] = useState(
    JSON.parse(localStorage.getItem(storageKey) || "null") || defaultValue
  );

  const wrappedSetValue = (newValue) => {
    localStorage.setItem(storageKey, JSON.stringify(newValue));
    setValue(newValue);

JoshuaCarroll

Alaska 
POLYGON((-141.0205 70.0187,-141.7291 70.1292,-144.8163 70.4515,-148.4583 70.7471,-151.1609 70.7923,-152.6221 71.1470,-153.9954 71.1185,-154.8853 71.4307,-156.7529 71.5232,-157.9449 71.2796,-159.6313 71.2249,-161.8671 70.6363,-163.5809 70.0843,-165.2399 69.3028,-166.8768 69.1782,-168.0414 68.3344,-165.9155 67.6844,-164.6082 67.2933,-164.0149 66.7789,-165.7507 66.5810,-167.5745 66.2867,-168.9862 66.0269,-168.9478 65.4970,-167.4756 65.0420,-167.0142 64.3922,-165.7343 64.0554,-163.2294 64.0193,-162.1143 63.9615,-163.6029 63.6877,-165.3717 63.4530,-166.3715 62.4133,-166.9867 61.6534,-166.4429 60.8556,-167.8381 60.5357,-167.7118 59.5482,-165.8002 59.4115,-164.5972 59.3696,-162.8558 59.1168,-162.5427 58.1185,-160.6421 58.1359,-159.5050 58.0285,-158.8953 57.6336,-159.9060 56.9090,-160.6531 56.3926,-161.8835 56.2342,-162.9822 55.7240,-164.3994 55.2478,-165.3168 54.7753,-167.1075 54.1463,-168.5852 53.5632,-169.9146 53.1402,-169.5959 52.5964,-168.2227 52.9089,-162.7734 54.2139,-159.1452 54.6786,-155.4634 55.656

SzieberthAdam

CREATE OR REPLACE FUNCTION st_extend (
    geom geometry,
    head_rate double precision,
    head_constant double precision,
    tail_rate double precision,
    tail_constant double precision)
  RETURNS geometry AS
$BODY$
-- Extends a linestring.
-- First segment get extended by length * head_rate + head_constant.

chamakits

javascript: function runDownloadThing(howManyToDownload) {
    if (!howManyToDownload) {
        howManyToDownload = 3;
    }
    if (window['downloadSome']) {
        window.downloadSome();
        return;
    }
    var iter = $('div.download a.a:not([download])').toArray();
    iter = iter.concat($('div.row a[download]').toArray());

dschep

#!/usr/bin/env python3
"""
More convinient than `python -c`.

Automatically imports python modules and prints the repr of the last statement.
for example:
    `py 'json.load(sys.stdin)'`
instead of
    `python -c 'import json,stdin;print(repr(json.load(sys.stdin)))`

dschep

Python list & dict comprehensions translated to JavasScript

Comprehensions are a really useful feature of Python that aren't available in JavaScript (or many languages). These concepts of course can be tranlsated into using map instead. But especially the dictionaries are a bit trickier.

Lists / Arrays

>>> foobar = range(5)
>>> [x + 1 for x in foobar]
[1, 2, 3, 4, 5]

dschep

Installing Python 3.6 on Raspbian

As of January 2018, Raspbian does not yet include the latest Python release, Python 3.6. This means we will have to build it ourselves, and here is how to do it. There is also an ansible role attached that automates it all for you.

1. Install the required build-tools (some might already be installed on your system).