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tools.realwallpaper: replace mercator by plate carrée world projection
Mercator at 16:9 only showed about +-71 degrees, cutting off northern
Greenland and the Arctic. The new variant world is plate carrée, north up,
centred on the equator and the home longitude, showing -90..90 degrees
stretched vertically to fill the screen. It replaces mercator in the CLI
--projection choices and the server's variant parameter, without an alias
for the old name. lens and plain are unchanged.
author
Hermes
committer
lassulus
date
(Oct 17, 2026, 12:30 AM CEST)
commit
0d32dfeb
0d32dfebee03e149ec3d8fe121f592c4dee0fa14
parent
8cce4990
8cce499076e63438147788585d97e5ae80e832ce
+28
-17
+24
-13
tools/realwallpaper/realwallpaper.py
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-13
tools/realwallpaper/realwallpaper.py
···
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Projections (--projection):
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- lens: the above plus the magnifying lens around home (default)
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- plain: the above without the lens, no distortion beyond the cylinder
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- mercator: the classic map, north up, true Mercator centred on the
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equator and the home longitude; the poles are cut off (about +-71
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degrees fit 16:9) and there is no lens
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- world: the classic map, north up, plate carrée centred on the equator
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and the home longitude, the whole globe stretched to fill the screen
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(longitude scaled to the width, latitude to the height); no lens
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The lens is focus + glue + context (Yamamoto et al. 2009; the same idea
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as Snyder's 1987 "magnifying-glass" azimuthal projections): a lens
···
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self.height = height
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self.m = magnification if projection == "lens" else 1.0
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self.k = 2 * math.pi / width # radians of longitude per px
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if projection == "mercator":
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self.world = projection == "world"
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if self.world:
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self.rot_lat = 0.0 # no rotation: the real equator is the axis
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self.a = 1.0 # true Mercator
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self.ky = math.pi / height # radians of latitude per px
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else:
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self.rot_lat = self.lat0 # home on the projection's equator
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self.a = solve_cylinder(math.pi * height / width)
···
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wx = self.px + dx * scale
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wy = self.py + dy * scale
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lon_r = (wx - self.px) * self.k
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u = (self.py - wy) * self.k
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lat_r = (2 / self.a) * (np.arctan(np.exp(self.a * u)) - math.pi / 4)
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if self.world:
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lat_r = (self.py - wy) * self.ky
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else:
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u = (self.py - wy) * self.k
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lat_r = (2 / self.a) * (np.arctan(np.exp(self.a * u)) - math.pi / 4)
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lat_r = np.clip(lat_r, -math.pi / 2, math.pi / 2)
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lat, dlon = rotate_from_home(self.rot_lat, lat_r, lon_r)
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lon = (self.lon0 + dlon + math.pi) % (2 * math.pi) - math.pi
···
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coarse = np.maximum(tangential, radial)
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lens_f = np.where(inside, np.maximum(fine, coarse / 4), 1.0)
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# cylinder: east-west px size R k cos(lat), north-south R k cos(a lat)
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base_f = np.maximum(np.cos(lat_r), np.cos(self.a * lat_r) / 4)
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q = R_EARTH * self.k * base_f * lens_f
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# (world: R ky)
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if self.world:
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base_q = np.maximum(self.k * np.cos(lat_r), self.ky / 4)
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else:
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base_q = self.k * np.maximum(np.cos(lat_r), np.cos(self.a * lat_r) / 4)
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q = R_EARTH * base_q * lens_f
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return np.degrees(lat), np.degrees(lon), np.maximum(q, 1e-3)
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def forward(self, lat_deg, lon_deg):
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lat = np.radians(np.asarray(lat_deg, dtype=np.float64))
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dlon = np.radians(np.asarray(lon_deg, dtype=np.float64)) - self.lon0
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lat_r, lon_r = rotate_to_home(self.rot_lat, lat, dlon)
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lat_r = np.clip(lat_r, -math.radians(89.5), math.radians(89.5))
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wx = self.px + lon_r / self.k
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wy = self.py - np.log(np.tan(math.pi / 4 + self.a * lat_r / 2)) / (self.a * self.k)
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if self.world:
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wy = self.py - lat_r / self.ky
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else:
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lat_r = np.clip(lat_r, -math.radians(89.5), math.radians(89.5))
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wy = self.py - np.log(np.tan(math.pi / 4 + self.a * lat_r / 2)) / (self.a * self.k)
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dx, dy = wx - self.px, wy - self.py
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r = self.norm(dx, dy)
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s = np.interp(np.minimum(r, 1.0), self._h, self._s)
···
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p.add_argument("--falloff", type=float, default=0.65,
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help="where across the lens (0..1) the distortion peaks; higher keeps "
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"the middle closer to a plain zoom (default 0.65)")
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p.add_argument("--projection", choices=["lens", "plain", "mercator"], default="lens",
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p.add_argument("--projection", choices=["lens", "plain", "world"], default="lens",
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help="lens: centred on home with the zoom lens; plain: centred on home "
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"without distortion; mercator: classic north-up map (default lens)")
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"without distortion; world: classic north-up map (default lens)")
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p.add_argument("--marker-url", default=None,
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help="JSON with {name: {latitude, longitude}} for krebs markers")
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p.add_argument("--time", type=dt.datetime.fromisoformat, default=None,
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-1
tools/realwallpaper/server-usage.kdl
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tools/realwallpaper/server-usage.kdl
···
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bin "realwallpaper-server"
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about "HTTP service rendering realwallpaper on demand: /?location=LAT,LON&variant=lens|plain|mercator&overlay=none|sky|krebs|stars&size=WxH"
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about "HTTP service rendering realwallpaper on demand: /?location=LAT,LON&variant=lens|plain|world&overlay=none|sky|krebs|stars&size=WxH"
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flag "--state-dir" help="Renders and the shared data cache (required)" {
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arg "<dir>"
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tools/realwallpaper/server.py
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tools/realwallpaper/server.py
···
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from dataclasses import dataclass, field
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from pathlib import Path
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VARIANTS = ("lens", "plain", "mercator")
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VARIANTS = ("lens", "plain", "world")
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OVERLAYS = {
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"none": "realwallpaper.png",
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"sky": "realwallpaper-marker.png", # sun, moon, planets
···
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location degrees, south/west negative, rounded to 0.01 (default Berlin)
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variant lens (zoomed in on location), plain (no distortion),
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mercator (classic north-up map) (default lens)
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world (classic north-up map) (default lens)
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overlay none, sky (sun, moon, planets), krebs (sky and krebs nodes),
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stars (all of that plus constellations) (default sky)
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size up to 3840x2160 (default 3840x2160)
+1
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tools/realwallpaper/usage.kdl
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tools/realwallpaper/usage.kdl
···
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flag "--falloff" help="Where across the lens (0..1) the distortion peaks; higher keeps the middle closer to a plain zoom (default 0.65)" {
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arg "<position>"
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}
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flag "--projection" help="lens: centred on home with the zoom lens; plain: centred on home without distortion; mercator: classic north-up map (default lens)" {
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flag "--projection" help="lens: centred on home with the zoom lens; plain: centred on home without distortion; world: classic north-up map (default lens)" {
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arg "<mode>"
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}
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flag "--marker-url" help="JSON {name: {latitude, longitude}} for krebs markers" {