Raycasting - Lode’s Computer Graphics Tutorial
Raycasting is a rendering technique to create a 3D perspective in a 2D map. Back when computers were slower it wasn’t possible to run real 3D engines in realtime, and raycasting was the first solution. Raycasting can go very fast, because only a calculation has to be done for every vertical line of the screen. The most well known game that used this technique, is of course Wolfenstein 3D.
The basic idea of raycasting is as follows: the map is a 2D square grid, and each square can either be 0 (= no wall), or a positive value (= a wall with a certain color or texture).
For every x of the screen (i.e. for every vertical stripe of the screen), send out a ray that starts at the player location and with a direction that depends on both the player’s looking direction, and the x-coordinate of the screen. Then, let this ray move forward on the 2D map, until it hits a map square that is a wall. If it hit a wall, calculate the distance of this hit point to the player, and use this distance to calculate how high this wall has to be drawn on the screen: the further away the wall, the smaller it’s on screen, and the closer, the higher it appears to be. These are all 2D calculations. This image shows a top down overview of two such rays (red) that start at the player (green dot) and hit blue walls.
Blue-eyed humans have a single, common ancestor
New research shows that people with blue eyes have a single, common ancestor. A team at the University of Copenhagen have tracked down a genetic mutation which took place 6-10,000 years ago and is the cause of the eye colour of all blue-eyed humans alive on the planet today.
Does your dad have blue eyes? Does your mom?
Just saying. . .
Astronomical Precession
Precessional movement as seen from ‘outside’ the celestial sphere
The precession of Earth’s axis of rotation with respect to inertial space is also called the precession of the equinoxes. Like a wobbling top, the direction of the Earth’s axis is changing; while today, the North Pole points roughly to Polaris, over time it will change. Because of this wobble, the position of the earth in its orbit around the sun at the moment of the equinoxes and solstices will also change.
The term precession typically refers only to the largest periodic motion. Other changes of Earth’s axis are nutation and polar motion; their magnitude is very much smaller.
Currently, this annual motion is about 50.3 seconds of arc per year or 1 degree every 71.6 years. The process is slow, but cumulative. A complete precession cycle covers a period of approximately 25,765 years, the so called Platonic year, during which time the equinox regresses a full 360° through all twelve constellations of the zodiac. Precessional movement is also the determining factor in the length of an astrological age.
Preferred Number
In industrial design, product developers must choose numerous lengths, distances, diameters, volumes, and other characteristic quantities. While all of these choices are constrained by considerations of functionality, usability, compatibility, safety or cost, there usually remains considerable leeway in the exact choice for many dimensions. Preferred numbers (also called preferred values) are standard guidelines for choosing exact product dimensions within such constraints.
They serve two purposes:
1. Using preferred numbers increases the probability that other designers will make exactly the same choice. This is particularly useful where the chosen dimension affects compatibility. For example, if the inner diameters of cooking pots or the distances between screws in wall fixtures are chosen from a series of preferred numbers, then it will be more likely that old pot lids and wall-plug holes can be reused when the original product is replaced.
2. Preferred numbers are chosen such that when a product is manufactured in many different sizes, these will end up roughly equally spaced on a logarithmic scale. They therefore help to minimize the number of different sizes that need to be manufactured or kept on stock.
Fine-tuned Universe
The fine-tuned Universe is the idea that conditions that allow life in the Universe can only occur with the tightly restricted values of the universal physical constants, and that if any of several fundamental constants were only slightly different the universe would be unlikely to be conducive to the establishment and development of matter, astronomical structures, elemental diversity, or life as it is presently understood.
The arguments relating to the fine-tuned universe concept are related to the anthropic principle, which states that any valid theory of the universe must be consistent with our existence as human beings at this particular time and place in the universe. In other words, even if the actual probability of a universe that supports intelligent life is very low, the conditional probability of supporting intelligent life, given our existence in it, is 1. Even if there could be other universes, less “fine-tuned” and so devoid of life, there would be no one there to observe them.
The premise of the fine-tuned universe assertion is that a small change in several of the approximately 26 dimensionless fundamental physical constants would make the universe radically different: if, for example, the strong nuclear force were 2% stronger than it is (i.e. if the coupling constant representing its strength were 2% larger), diprotons would be stable and hydrogen would fuse into them instead of deuterium and helium. This would drastically alter the physics of stars, and presumably prevent the universe from developing life as it is currently observed on the earth. However, many of the 26 constants describe the properties of the unstable strange, charmed, bottom and top quarks and mu and tau leptons which seem to play little part in the universe or the structure of matter. It seems unlikely that the precise values of these constants are important for life; at any rate they are not included in the usual discussion of fine-tuning.
Barn (unit of measure)
A barn (symbol b) is a unit of area. While the barn is not an SI unit, it is accepted (although discouraged) for use with the SI. Originally used in nuclear physics for expressing the cross sectional area of nuclei and nuclear reactions, today it is used in all fields of high energy physics to express the cross sections of any scattering process. A barn is approximately equal to the cross sectional area of a uranium nucleus. The symbol b is also used by the IEEE to represent the bit.
The etymology is clearly whimsical—the unit is said to be “as big as a barn” compared to the typical cross sections for nuclear reactions. During wartime research on the atomic bomb, American physicists who were bouncing neutrons off uranium nuclei described the uranium nucleus as “big as a barn.” Physicists working on the project adopted the name barn for a unit equal to 10-24 square centimetres, about the size of a uranium nucleus. Initially they hoped the American slang name would obscure any reference to the study of nuclear structure; eventually, the word became a standard unit in particle physics.
Mendenhall Order
The Mendenhall Order marked a decision to change the fundamental standards of length and mass of the United States from the customary standards based on those of England to metric standards. It was issued on April 5, 1893 by Thomas Corwin Mendenhall, superintendent of the U.S. Coast and Geodetic Survey, with the approval of the United States Secretary of the Treasury, John Griffin Carlisle. The order was issued as the Survey’s Bulletin No. 26 - Fundamental Standards of Length and Mass.
In 1866 the Congress passed a law which allowed, but did not require, the use of the metric system. Included in the law was a table of conversion factors between the traditional and metric units. The U.S. Coast and Geodetic Survey Office of Weights and Measures had on hand a number of metric standards, and selected the iron “Committee Meter” and the platinum “Arago Kilogram” to be the national standards for metric measurement; the standard yard and pound previously mentioned continued to be the standards for customary measurements.
A series of conferences in France between 1870 and 1875 lead to the signing of the “Metric Convention” in 1875, and to the permanent establishment of the International Bureau of Weights and Measures, abbreviated BIPM after the French name. The BIPM made meter and kilogram standards for all the countries that signed the treaty; the two meters and two kilograms allocated to the United States arrived in 1890, and were adopted as national standards.
The imperial standard yard of 1855 was found to be unstable and shortening by measurable amounts. Also, the mint pound was found to be “likewise unfit for use.” For several years before the Mendenhall order was actually issued, the Office of Weights and Measures was “practically forced” to use the metric standards because of their superior stability, and because they were better designed for carrying out precision comparisons. The Office found that the conversion tables in the 1866 law were satisfactory and used them to derive customary length and mass from the metric standards. The conversions were 1 yard = 3600/3937 meter and 1 pound = 0.4535924277 kilogram. The Mendenhall order amounted to a formal announcement of a change that had already occurred.
<$20 Screwdriver Bit Set
Seriously, the last screwdriver bit set you will ever need. Ive been looking for one of these for a long time. Besides all your standard philips, hex, Torx, and square head bits in every imaginable size from tiny to gimungus it also includes a whole ton of “security” bits, including those for secure hex, secure Torx, those crazy one-way philips-head screws you see in public bathrooms, and a few others Ive never even seen before.
With this kit, you can take apart just about any piece of electronic hardware youre likely to encounter. And it was only $16 at Frys. Definitely a must-have.
I’ve never noticed what screws hold public bathrooms together, but I will definitely take a look tomorrow.
It’s on indefinitely backorder from Fry’s, but there are a few other places online that have it in the comments.
With this screwdriver bit set… I can take apart the universe [via]
Avoirdupois
The avoirdupois system is a system of weights (or, properly, mass) based on a pound of sixteen ounces. It is the everyday system of weight used in the United States. It is still widely used by many people in Canada and the United Kingdom despite the official adoption of the metric system, including the compulsory introduction of metric units in shops. It is considered more modern than the alternative troy or apothecary or the medieval English mercantile and Tower systems.
The word avoirdupois is from French and Middle English (Anglo-French) avoir de pois, “goods of weight” or “goods sold by weight”, and from Old French aveir de peis, literally “goods of weight”, from aveir, “property, goods” (from aveir, “to have”, from Latin habere, “to have, to hold, to possess property”) de, “from” (from the Latin) peis, “weight”, from Latin pensum, “weight”. This term originally referred to a class of merchandise: aveir de peis, “goods of weight”, things that were sold in bulk and were weighed on large steelyards or balances. Only later did it become identified with a particular system of units used to weigh such merchandise. The imaginative orthography of the day and the passage of the term through a series of languages (Latin, Anglo-French and English) has left many variants of the term, such as haberty-poie and haber de peyse.
Squircle
A squircle is a mathematical shape with properties between those of a square and those of a circle.
Amanda noticed me post this and mentioned that our new plates are squircles. Sure enough, Wikipedia noticed as well.
Squircles have also been used to construct dinner plates. A squircular plate has a larger area (and can thus hold more food) than a circular one with the same radius, but still occupies the same amount of space in a rectangular or square cupboard. The same is true of a square plate, but there are various problems (such as wiping up sauce) associated with the corners of square plates.
Squircle - Wikipedia, the free encyclopedia (Thanks, Garrett!)