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90 posts tagged with geometry.

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## Finding near-misses between lines in 3D

Is there a good (read: well-known/efficient) way to find the "near-miss" intersection of 3 lines in 3D space? The lines almost, but don't quite, cross each other (image in an attempt to illustrate the problem) [more inside]

## math/geometry/construction query!

Suppose you have to install new moulding in a house. Suppose also that it's a huge house with many rooms large and small, and many windows of different size. This means that you end up needing many different lengths of wood... [more inside]

## Formula to get the diameter of multiple circles to surround a larger one

I am doing an art project that requires larger circles to be encircled by smaller circles. Each small circle must touch its larger one and its immediate small neighbors. The small circles must all be the same diameter. I would like to specify the diameter of the large circle and calculate the diameter and number of small circles required to accomplish the desired outcome. My geometry skills have eroded over these many years...help!

## Fano Plane and Hexagonal Tiling - a deep connection or a shallow one?

I've been chewing on the Fano plane a lot these last few weeks, and have just noticed something that seems really interesting to me. Notably, that the seven lines of the plane map very nicely to the 7-color hexagonal tiling. [more inside]

## Is there a name for this shape?

What would you call the shape of the two-dimensional outline of the two stones (cabochons) circled in red in this picture? [more inside]

## Books/review of high school math for former math major, current tutor

I need book recommendations two categories:
1) for myself for review (that are somewhere between high school text books and Spark notes)
2) just straight up textbooks for high school math (algebra i, geometry, algebra ii, trigonometry, pre-calculus) [more inside]

## I know enough calculus to think of the question but not the answer

You want to walk 10 blocks north and 10 blocks east. It would be shorter to walk along the hypotenuse, but the same distance to walk 1 block north, then 1 block east, then 1 block north, etc. it seems that if the blocks were infinitesimally short, it would approximate the hypotenuse, but alas, walking 10 blocks in one direction and then 10 blocks in the perpendicular direction is the same as dividing it up. What gives?

## Printing polygonal puzzle pieces

I'd like to have polygonal pieces made for an (essentially) flat dissection puzzle similar to this nice-looking tangram set at Shapeways. The pieces are simple, but I could use some guidance / tips on the whole process of bringing them into existence. [more inside]

## Vicarious Math Pressure

My eldest child is starting high school. She is in the most advanced math class (a version of geometry) offered by her fairly demanding high school. But my eldest is struggling during the review of algebra -- rate problems, word problems, etc. Concerned because math is cumulative, and I don't want her falling behind. What can I do to help, both with math and with preventing her from becoming discouraged? [more inside]

## Calculating interior angles of an irregular hexagon?

I'm trying to create a 3D model of a six-sided area of my garden. I know the lengths of each side. Is it possible to work out the exact angle of each corner?
Here's a link to a rough picture - note that the labels are correct but the sides and angles aren't to scale. [more inside]

## Help with 2D transforms in ellipse drawing algorithm

I'm trying to draw a 3D ellipse with a 2.5D graphics engine (Core Animation layers) which allow me to only compose my ellipse with line segments that must be moved into place using rotations and translations. I'm having trouble with the order of operations and can't get it to draw properly. Any graphics gurus or game programmers out there who can help me? [more inside]

## German female artist, specializing in fine geometric lines?

A few years ago, I came across the website of a German artist, female, who specialized in creating geometric artwork featuring very fine lines (think sweeping, 1pt lines). The only other things I remember are: 30ish in age, and had a non-standard German name, e.g. not something simple like "Anna Schmid". Anyone know her name and site?

## Pythagorean Theorem in the original Greek

I'm looking for a textual version of

*a*^{2}+*b*^{2}=*c*^{2}that is as old as possible, among all the Greek sources. [more inside]## Tools For the Spatially Challenged: Couch-Movers Edition

Wizards of Hive,
Before I buy that 90" couch from a friend, how can I make sure I'll be able to get it up my L-shaped stairs? Sure, there are a lot of variables. But is there a tool or methodology for figuring this out ahead of time (presuming I know the depth and height of the couch too)? I don't think I have the cardboard to build a mockup.
This couch is 50 miles away and can't be returned. Thanks!

## Longitude lines in perspective, what shape are they?

I'm drawing/painting a globe (in time lapse, so the sun appears to rise) and trying to figure out what shape, exactly, the longitude (not latitude) lines are when a globe is flattened into a circle (I know I can just trace them, but I've gotten curious). So, the outermost longitude lines are tangent to the circle, they are half-circles, and the centermost line is a straight line from pole to pole, it's the progressively flatter curves in between that I'm trying to figure out. Do they have a name? Are they catenaries? Are they the curves of progressively larger circles? How do I construct them (easily)? Example image: HERE

## What is the point at this!

Here’s a simple computational geometry problem. I am trying to figure out the value at an point of two line segments based off of the values at both of one of the segment’s endpoints.
The problem is that I don’t exactly know the best way of going about finding the value at one of those points.
Here is a reference figure.
Given values
(X_C, YC) = F_C
(X_D, YD) = F_D
How can I calculate the value of F_E, where F_E = (X_E, Y_E), where E is the point on the segment CD, where CD intersects with the line AB?
(Extraneous details inside) [more inside]

## Learning geometry from television

Help me remember this old video series that used early computer/video animation to illustrate geometry/calculus concepts. [more inside]

## Math is Hard (I need help)

Math is hard. Please help me with a slope-related problem. [more inside]

## The Limits of Flatness

Are there an infinite number of 2D shapes? [more inside]

## Identifying urban centers using an algorithm based on topological prominence

Calling geographers: has anyone applied the idea of topological prominence to population density? [more inside]

## 3D graphics in a 2D context (for dummies)

HTML5 canvas question: I'm trying to model a 2D grid in 3D space and it's not working right. Can you help? [more inside]

## What is this geometric figure?

What is this geometric figure?
Is there a name for the figure inscribed in the circle here?

## Drag and Drop glued to polygon sides

Looking for tips on implementing drag and drop that snaps to the nearest point on a polygon. [more inside]

## Mr. Math Monster, I presume?

Help me to learn math as an adult when I still despise the frustrating beast from my childhood! [more inside]

## I need an awesome topic relating to maps/geometry!

I'm looking for an awesome video/discussion topic that relates to street maps - something appropriate for a HS geometry course. [more inside]

## What was this geometric creature builder website?

Several years ago, I saw a website with a fun little flash or javascript applet thingy where you could build little tensegrity structure creatures, then have oscillating movements applied to the pieces, so that the structures would seem to "walk". I don't remember what it was called! From memory, one of the simpler structures looked sort of like this. What was it? Is it still online? [more inside]

## I still KNOW the quadratic equation, just not what it means

I have forgotten basically all of math, and I want to learn it again from the ground up. [more inside]

## Seperating Interlocked Rings

Consider two rings that are intertwined. (These lie in 3-dimensional space, but when you draw it on paper it looks like a venn diagram.) In 3-dimensional space they cannot be unlinked. The questions is, if you had one more dimension, can you unlink them?

## Hypotewhat? Pythatgowho?

Geometry question -> Determine X and Y from distance along a straight line, or, how do I find the lengths of A and B if I know the length of C and the ratio of A to B in a right triangle? [more inside]

## For best fireworks viewing, please use Math.

I'd like to be able to watch the Macy's fireworks from my dad's roof on the Upper West Side. How can I figure out if I'll be able to see them? I have some variables, heights, distances, and video... [more inside]

## / \

Identify triads in writing? [more inside]

## Life inside a hyperbolic plane?

How does walking around on a hyperbolic plane differ from a euclidean one? [more inside]

## Geometry question about planes and cylinders.

Could someone help me with this geometry problem? Cylinder with a plane bisecting it at a 45° angle... [more inside]

## Formula to mesh two gears of arbitrary tooth count/position?

I'm writing a graphics app where I'm generating a simple gear transmission system with a variable number of gears each with variable number of teeth and placed at random orbits around each other. I generate gears in succession, placing and rotating each with respect to its parent/driver gear before moving on to the next. The problem I'm having is how to determine the initial orientation of each subsequent gear such that its teeth are properly meshed with that of its driver. [more inside]

## Blowing bubbles on a plane

Given a set of points on a plane (or in a bounded region), how do I find the radii of circles centered at each point that provide the best covering? [more inside]

## Shape identification question

What is this shape (the one in white) called?

## How to colour the tetrahedra in a chain of 24 to produce a rhombic dodecahedron?

How should I colour each isocoles tetrahedron in a chain of 24 using three colours, so that when I fold up the chain into a rhombic dodecahedron each rhombic face is a single colour and is different to its neighbours? [more inside]

## HOWTO: cylindrical map projection?

I want a flat, rectangular image that is a cylindrical map projection of the edges of a icosidodecahedron. How do I make one? [more inside]

## Cutting a perfect circle.

Cutting an 8" circle? [more inside]

## An awesome vector geometry teaching website

I'm trying to find a website that teaches vector mathematics in lesson form. [more inside]

## Regular tessellations of Euclidean spaces

MathFilter: Is there a relationship between the number of dimensions in a Euclidean space and the number of regular tessellations of that space? [more inside]

## Here's looking at Euclid.

Where can I find free geometry text diagram creating software? Even not so free software seems to not do what I want. I want to be able to draw simple plane geometry figures (e.g. right triangles) with markings (e.g. to indicate lines are perpendicular or angles are equal) and labels (e.g. of a line's length or the name of an angle) and such. [more inside]

## Contemporary Geometry: does it exist?

Contemporary Geometry: does it exist? [more inside]

## What is a triangular graph with axes perpendicular to the sides called?

What is the graph or plot called which:
- is an equilateral triangle
- has three axes
- each axes is perpendicular to a side of the triangle? [more inside]

## Geometry Wars Retro Evolved Controller Config

Geometry Wars Filter: Help configure Nyko Airflo PC game controller for Geometry Wars Retro Evolved (PC) [more inside]

## Photoshop Question: is there a way to get a count of pixels contained within any (irregularly shaped) selection/layer?

Photoshop Question: is there a way to get a count of pixels contained within any (irregularly shaped) selection/layer? [more inside]

## Four of the clock it was, so I as I guesse

How can I estimate the time that a photo was taken? [more inside]

## Stained Glassy Collages?

What software can I use to make a photo collage using non-rectangular photos? [more inside]

## 3D GeometryFilter: Is there a mathematical equation that defines relative lengths of objects at different depths of field for humans?

Is there an equation that defines the change in apparent size as a function of distance from the viewer? Basically, if I'm looking at a set of railroad tracks head on, if one plank is like 10 ft away, it appears to be one size. The same plank 20 ft away appears smaller. What is the relative size difference? Put another way, how big does a 1ft line appear to be at 10 ft, at 20 ft, etc.? [more inside]

## Get thee gone, my polygon

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