Fix character volume calculation

src/character.cpp

@@ -3102,15 +3102,23 @@ units::volume Character::get_total_volume() const
 
 units::volume Character::get_base_volume() const
 {
-    const int your_height = height(); // avg 175cm
-    // Arbitrary number picked relative to aisle (100L), not necessarily accurate
-    const units::volume avg_human_volume = 70_liter;
-
-    // Very scientific video game size to metric human volume calculation. Avg height == avg_human_volume;
-    units::volume your_base_volume = units::from_liter( static_cast<double>( your_height ) / 2.5 );
-    double volume_proport = units::to_liter( your_base_volume ) / units::to_liter( avg_human_volume );
-
-    return std::pow( volume_proport, 3.0 ) * avg_human_volume;
+    // The formula used here to calculate base volume for a human body is
+    //     BV = W / BD
+    // Where:
+    // * BV is the body volume in liters
+    // * W  is the weight in kilograms
+    // * BD is the body density (kg/L), estimated using the Brozek formula:
+    //     BD = 1.097 – 0.00046971 * W + 0.00000056 * W^2 – 0.00012828 * H
+    // See
+    //   https://en.wikipedia.org/wiki/Body_fat_percentage
+    //   https://calculator.academy/body-volume-calculator/
+    const int your_height = height();
+    const double your_weight = units::to_kilogram( bodyweight() );
+    const double your_density = 1.097 - 0.00046971 * your_weight
+                                + 0.00000056 * std::pow( your_weight, 2 )
+                                - 0.00012828 * your_height;
+    units::volume your_base_volume = units::from_liter( your_weight / your_density );
+    return your_base_volume;
 }
 
 units::mass Character::weight_carried() const

tests/char_volume_test.cpp

@@ -44,19 +44,23 @@ TEST_CASE( "character_baseline_volumes", "[volume]" )
     Character &you = get_player_character();
     REQUIRE( you.get_mutations().empty() );
     REQUIRE( you.height() == 175 );
-    CHECK( you.get_base_volume() == 70_liter );
+    CHECK( ( you.get_base_volume() > 55_liter && you.get_base_volume() < 80_liter ) );
 
     REQUIRE( your_height_with_trait( trait_SMALL2 ) == 70 );
-    CHECK( your_volume_with_trait( trait_SMALL2 ) == 4480_ml );
+    CHECK( ( your_volume_with_trait( trait_SMALL2 ) > 20_liter &&
+             your_volume_with_trait( trait_SMALL2 ) < 30_liter ) );
 
     REQUIRE( your_height_with_trait( trait_SMALL ) == 122 );
-    CHECK( your_volume_with_trait( trait_SMALL ) == 23717_ml );
+    CHECK( ( your_volume_with_trait( trait_SMALL ) > 40_liter &&
+             your_volume_with_trait( trait_SMALL ) < 50_liter ) );
 
     REQUIRE( your_height_with_trait( trait_LARGE ) == 227 );
-    CHECK( your_volume_with_trait( trait_LARGE ) == 152778_ml );
+    CHECK( ( your_volume_with_trait( trait_LARGE ) > 100_liter &&
+             your_volume_with_trait( trait_LARGE ) < 120_liter ) );
 
     REQUIRE( your_height_with_trait( trait_HUGE ) == 280 );
-    CHECK( your_volume_with_trait( trait_HUGE ) == 286720_ml );
+    CHECK( ( your_volume_with_trait( trait_HUGE ) > 150_liter &&
+             your_volume_with_trait( trait_HUGE ) < 200_liter ) );
 }
 
 TEST_CASE( "character_at_volume_can_or_cannot_enter_vehicle", "[volume]" )
@@ -66,8 +70,6 @@ TEST_CASE( "character_at_volume_can_or_cannot_enter_vehicle", "[volume]" )
     map &here = get_map();
     Character &you = get_player_character();
     REQUIRE( you.get_mutations().empty() );
-    REQUIRE( you.get_base_volume() == 70_liter );
-    REQUIRE( you.get_total_volume() == 70_liter );
 
     tripoint test_pos = tripoint{10, 10, 0 };
 
@@ -107,15 +109,15 @@ TEST_CASE( "character_at_volume_can_or_cannot_enter_vehicle", "[volume]" )
     cramped = false;
 
     // Try the cramped aisle with a rock again, but now we are tiny, so it is easy.
-    CHECK( your_volume_with_trait( trait_SMALL2 ) == 4480_ml );
+    CHECK( your_volume_with_trait( trait_SMALL2 ) == 23326_ml );
     you.setpos( test_pos ); // set our position again, clear_avatar() moved us
     dest_loc = dest_loc + tripoint_north;
     CHECK( you.can_move_to_vehicle_tile( dest_loc, cramped ) );
     CHECK( !cramped );
     dest_loc = you.get_location(); //reset
 
     // Same aisle, but now we have HUGE GUTS. We will never fit.
-    CHECK( your_volume_with_trait( trait_HUGE ) == 286720_ml );
+    CHECK( your_volume_with_trait( trait_HUGE ) == 156228_ml );
     you.setpos( test_pos ); // set our position again, clear_avatar() moved us
     dest_loc = dest_loc + tripoint_north;
     CHECK( !you.can_move_to_vehicle_tile( dest_loc ) );