Daniel Schep dschep

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

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]

	console.log(parse(`(define (square x)
	"Function calculate square of a number"
	(* x x))`)[0].toString());

	// ==> (define (square x) "funkcja square wywołanie (square 10) zwraca 100" (* x x))

	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

	-- 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;

	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);

	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.


	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

	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());

	#!/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)))`