Added earth surface texture

scripts/make-example-scenes.py

@@ -5,9 +5,15 @@ Every scene has the same composition: the spacecraft in an isometric view (the
 camera looks along its body (+1, +1, +1) diagonal, body +Z toward image up) with
 Earth's limb crossing the image 2 degrees above center, Earth below and space
 above. The camera distance makes the model's bounding sphere span about 5.6
-degrees, half the example camera's width. The Sun direction is the one, on a
-3-degree grid, that best lights the three visible body faces and Earth near the
-limb, without putting the spacecraft in Earth's shadow.
+degrees, half the example camera's width.
+
+Earth is turned so the ground behind the spacecraft, at the image center, is
+25 N 33 E (Egypt, the Nile and the Red Sea), with the camera looking north
+toward the Mediterranean on the limb. The Sun is the direction, on a 2-degree
+grid, that puts it at least 58 degrees above that ground (cos i >= 0.85) and
+best lights the spacecraft's three visible faces, without putting the
+spacecraft in Earth's shadow. With the Sun that high over the ground, one face
+is lit at a slant.
 
 Model centers and radii were measured from the decoded files at the listed
 scales (the bounding box of every vertex); remeasure if a model changes.
@@ -18,6 +24,10 @@ import pathlib
 import textwrap
 
 RE = 6378137.0
+# The ground at the image center, geocentric latitude and longitude in degrees.
+GROUND = (25.0, 33.0)
+# The least cos(incidence) the Sun may have on that ground.
+GROUND_SUN = 0.85
 AU = 1.495978707e11
 LEO = 7.0e6
 GEO = 42_164_000.0
@@ -105,20 +115,29 @@ def scene(name, file, scale, center, radius, orbit, description):
     offset = mul(attitude, center)
     position = [look[i] - offset[i] for i in range(3)]
 
-    to_limb = [-math.cos(limb), math.sin(limb), 0.0]
-    reach = math.sqrt(orbit * orbit - RE * RE)
-    limb_normal = norm([look[i] + reach * to_limb[i] for i in range(3)])
+    # The ground behind the spacecraft at the image center: where the boresight,
+    # continued past the spacecraft, meets Earth.
+    b = dot(look, boresight)
+    reach = -b - math.sqrt(b * b - (dot(look, look) - RE * RE))
+    ground = norm([look[i] + reach * boresight[i] for i in range(3)])
+    # Turn Earth so GROUND is there, with north along the camera's view across it.
+    lat, lon = (math.radians(x) for x in GROUND)
+    fixed = [math.cos(lat) * math.cos(lon), math.cos(lat) * math.sin(lon), math.sin(lat)]
+    north = norm([boresight[i] - dot(boresight, ground) * ground[i] for i in range(3)])
+    earth = triad(fixed, [0, 0, 1], ground, north)
+
     best = None
-    for az in range(0, 360, 3):
-        for el in range(-87, 90, 3):
+    for az in range(0, 360, 2):
+        for el in range(-88, 90, 2):
             a, e = math.radians(az), math.radians(el)
             sun = [math.cos(e) * math.cos(a), math.cos(e) * math.sin(a), math.sin(e)]
             if dot(sun, [-1.0, 0.0, 0.0]) > math.cos(limb):
                 continue  # behind Earth: the spacecraft would be in shadow
+            if dot(ground, sun) < GROUND_SUN:
+                continue
             faces = [dot(mul(attitude, n), sun) for n in ([1, 0, 0], [0, 1, 0], [0, 0, 1])]
-            score = min(min(faces), dot(limb_normal, sun))
-            if best is None or score > best[0]:
-                best = (score, sun)
+            if best is None or min(faces) > best[0]:
+                best = (min(faces), sun)
     sun = best[1]
 
     fmt = lambda v, d=2: "[" + ", ".join(f"{x:.{d}f}" for x in v) + "]"
@@ -131,15 +150,22 @@ def scene(name, file, scale, center, radius, orbit, description):
     return f"""{header}
 #
 #   resolved render --scene examples/scenes/{name}.toml --preview {name}.png
+#   resolved render --scene examples/scenes/{name}.toml --lighting L1 --preview {name}.png
 
 sun = {fmt([AU * x for x in sun], 0)}
 moon = [0, 0, -3.844e8]
+# Earth-fixed to inertial: 25 N 33 E behind the spacecraft, looking north.
+earth_attitude = {fmt(quaternion(earth), 9)}
 
 [observer]
 position = {fmt(camera)}
 look_at = {fmt(look)}
 up = [1, 0, 0]
 
+# At lighting L1, Earth's surface shows July (from scripts/fetch-earth.sh).
+[appearance]
+earth_month = 7
+
 [[target]]
 model = "../models/nasa/{file}"
 scale = {scale}