Questions tagged [orientation]
For question regarding the notion of orientation both in topology and in global analysis.
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Question related to orientation on a arbitrary oriented manifold
This is a section from Loring Tu's book Introduction to Manifolds page 244 Second Edition. My question is as follows:
Towards the end of the text in the image he says that an oriented manifold can be ...
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On the unit sphere $S^2$, show the antipodal map $A:S^2\to S^2$ is orientation reversing using definitions.
I want to show that on the unit sphere $S^2$, the antipodal map $A:S^2\to S^2$ given by $(x,y,z) \mapsto (-x,-y,-z)$ is orientation reversing.
I know that $S^2$ is a regular connected orientable ...
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25 views
Pairings of Simplex Edges
This is an open-ended question. If you'll allow, I'd like to keep its origins vague for the moment, so as not to bias responses. I am interested in any and all thoughts.
There are three pairings of ...
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Angular error (in Euler angles) through quaternions
I found this formula in some notes but I would like to have a reference (book, paper, etc.) to understand where it comes from. I know that it works only for small angles.
$
\begin{bmatrix}
\phi_e\\
\...
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1answer
99 views
Every connected orientable smooth manifold has exactly two orientations, Lee Proposition 15.9
The proof of Proposition 15.9 from John Lee's book "Introduction to Smooth Manifolds" is left as an exercise.
Here is the statement:
Let $M$ be a connected, orientable, smooth manifold with or ...
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31 views
Why should one think of orientation as a homology class?
Let $\pi:E\rightarrow B$ be a smooth vector bundle. I call this vector bundle to be an oriented vector bundle, if I can choose an orientation on $\pi^{-1}(b)$ for each $b\in B$ and a trivialization ...
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15 views
Rotation with roll pitch and yaw in different coordinate system
Say I am given a point in an x1,y1,z1 coordinate system. I have a different coordinate system, x2,y2,z2 that has the same origin as the x1,y1,z1 system, but the axis are not aligned. I have roll, ...
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Torque required to achieve a desired quaternion
I was hoping someone can either explain or direct me towards a source that can help me with the following problem (not for homework, more of a hobby).
Given an object with a current quaternion $q_c$ ...
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54 views
Diffeomorphism Between Surfaces Preserves Orientability
From Do Carmo (Exercise 2.6.2).
Let $S_2$ be an orientable regular surface and $\varphi:S_1\rightarrow S_2$ be a local diffeomorphism at every $p\in S_1$. Prove $S_1$ is orientable.
Up until this ...
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1answer
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understanding orientable manifolds
I'm reading Warner. "Foundations of Differentiable Manifolds and Lie Groups." p. 138. I don't get the statement in the definition of orientable manifolds.
4.1 Definitions $\;$ (the preface omitted) ...
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Determine orientation of standard orthonormal bases
Let $\vec{e_1},\vec{e_2},\vec{e_3}$ be the standard orthonormal base $(1,0,0),(0,1,0),(0,0,1)$ which is positively oriented. Determine the orientation of each of the following bases:
$\vec{e_1},\vec{...
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Orientation of a Manifold with Trivial Tangential Bundle
Let $M$ be a smooth (eg $C^{\infty}$) manifold. Let assume that $M$ has trivial, oriented tangent bundle $TM$, so $TM \cong M \times \mathbb{R}^n$ for appropriate $n$ and orientable.
How to conclude ...
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Finding and Comparing 2 Sensors Rotations, with same reference frame but different initial Orientation
Let's say we want to Compare two different Arm (Humerus) Rotations (series of quaternions) and we do not care about space translation but only for rotation. To measure each rotation we use the same ...
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The orientation induced on the boundary of a manifold.
I just learned about the notion of orientability of a manifold which is difficult and abstract for me. If we consider all basis of a vector space, the matrix that transforms one basis in another basis ...
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Id $f,g$ orientation preserving cricle-diffeomorphisms, then $\rho(g^{-1}\circ f \circ g) = \rho(f)$.
Let $F, G : \mathbb{R} \rightarrow \mathbb{R}$ be a lift of $f$ and $G$ of $g$. That is, $ \pi \circ F = f \circ \pi$ with $\pi(x) = e^{2\pi i}$. We define $$\rho_{0}(F) = \lim_{n\rightarrow \infty}\...
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43 views
Smallest rotation angle between quaternions accounting for symmetry
I am trying to compute a similarity measure between the orientation of 3D objects accounting for symmetry invariance. I have a set of 3D objects, which are defined by a center of mass, and 3 unit ...
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38 views
Prove that an integration is left invariant.
$G$: Lie group of dimension $n$.
$\tilde{\Omega}$: Orientation on $G$.
$\Omega=\epsilon^1\wedge \epsilon^2\wedge \cdots \wedge \epsilon^n$ where $\epsilon^1\, \epsilon^2, \cdots ,\epsilon^n$ is ...
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Sard's theorem for orientation preserving diffeomorphism of the circle
thanks in advance for helping me. First I'll introduce some definitions:
(1) Suppose that $f : \mathbb{S}^{1} \rightarrow \mathbb{S}^{1} = \mathbb{R} / \mathbb{Z}$ is an orientation preserving ...
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1answer
29 views
If $(e_1, \ldots, e_n)$ and $(f_1, \ldots, f_n)$ are co-oriented, then so are $(e_1, \ldots, e_n, u)$ and $(f_1, \ldots, f_n, u)$
Suppose that $S$ is a smooth $n$-submanifold of $M$ where $\dim(M) = n+1$. Suppose also that $S$ and $M$ are both Riemannian and oriented.
Suppose that $(e_1, \ldots, e_n)$ and $(f_1, \ldots, f_n)$ ...
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1answer
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Show that $\mathbb{S}^{n+m}$ is not homeomorphic to a product of orientable manifolds
I want to prove that the sphere $\mathbb{S}^{n+m}$ is not homeomorphic to the product of N and M, orientable manifolfs with $\textit{dim}\;N=n$ and $\textit{dim}\;M=m$. I know that I have to use the ...
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1answer
35 views
How/why does the contraction of standard volume form give the canonical form.
$M \subset \mathbb{R}^{N}$ is a (oriented) $n-1$ dimensional submanifold. Suppose $\nu \in T_{p}M^{\bot}$, of length one (a normal unit vector on $M$).
How and why does the contraction $\nu_{\neg}(...
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Submanifold of codimension 1 orientable iff there exists unit normal vector field.
Suppose I have a submanifold $M \subset \mathbb{R}^{n}$, of dimension $n-1$. Where a unit normal vector field is a section $\nu$ of the normal bundle $ TM^{\bot} \to M$. So the fibers are all the ...
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2answers
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Every submanifold is orientable (co-dimension 1)?
Suppose I have a submanifold $M \subset \mathbb{R}^{n}$, of dimension $n-1$. Apparently it's orientable if and only if there exists a unit normal vector field on $M$. Where a unit normal vector field ...
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1answer
31 views
If $TM$ is trivial, then $\Lambda^n(M)$ is also trivial and $M$ is orientable
Suppose that $M$ is a smooth $n-$manifold. Suppose $$ TM=\coprod_{p\in M}T_pM $$ is the tangent bundle of $M$. And let $$ \Lambda^n(M)=\coprod_{p\in M}\Lambda^n(T_pM) $$ where $\Lambda^n(T_pM)$ is ...
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1answer
31 views
What is the direction of a rotation?
We usually talk about rotations in the clockwise or counterclockwise direction. But if a rotation is just a function defined on the space, then it is all about points and their images, and there is no ...
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19 views
Prove that the following function is an orientation of a curve
Assume that $f^{(j)}:\mathbb{R}^3\rightarrow \mathbb{R}$ for $j=1,2$ are some $C^1$ functions such that $(\nabla f^{(1)}, \nabla f^{(2)})$ are independent over the curve $\gamma = \{ x \in \mathbb{R}^...
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Orientation of 4 + 1 lines in $\mathbb{R}^3$.
I'm working on a 3D algorithm that at some point establishes orientation of two lines - the same way one would do using the triple product. The way those lines are described, however, makes the ...
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Create Wall 3D math oriented away from camera
I have 2 Points which has x,y,z let's say from and to I am drawing wall between them using ARkit ios
To draw wall I use static ...
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Visualisation of an orientable surface bounded by the Möbius curve
I'm learning multivariable calculus on MIT OpenCourseWare. When the teacher explained Stokes theorem he mentioned the Möbius strip. He showed it was non-orientable. Then he showed a somehow twisted ...
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1answer
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Orientable manifold $M$ ,then $\partial M$ is orientable
Let $M$ a topological manifold of dimension $n$ with boundary $\partial M$.
We define $M$ to be orientable if $M- \partial M$ is orientable. Here when I say orientable, I mean there is a locally ...
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preserves or reverse orientation of sphere surface
Let $\varphi: (0, \infty) \times (0, \pi) \times (0, 2 \pi) \to \mathbb{R}^3 \setminus \{(x,y,z) \in \mathbb{R}^3| y=0, x \geq 0 \}$
$$(p,\phi,\theta) \mapsto (p \sin \phi \cos \theta, p \sin \phi \...
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1answer
32 views
Find the angles between two solids
I have 2 solids (A and B) and I need to find the three angles between their x, y, and z axes. If I calculate the geometrical center of the two solids (Ax, Ay, Az and Bx, By, Bz), is it correct to ...
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1answer
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Orientation in the proof of Stokes Theorem
I'm reading the proof of Stokes theorem at page 83 of "Godinho, Natàrio, An introduction to Riemannian geometry" and I can't understand a passage in it, probably because the definition of ...
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1answer
40 views
Prove there exists a outward unit normal field on the boundary this manifold
Let $M$ be a compact subset of $\mathbb{R}^3 $ with the standard orientation $\mu =[e_1,e_2,e_3] $ and let $S = \partial{M}$ is its smooth boundary with the induced orientation from $M$. Prove there ...
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Null homologous loop and orientable surface
I am reading Algebraic Topology: A First Course written by Greenberg and Harper. On page 67 of this book it is stated that
Let $\gamma$ be a loop in $X$ regarded as a map $f:S^1\to X$. For $\chi[\...
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1answer
42 views
Smooth isotopy preserves orientation
Let $N$ a $n$-dimensional connected manifold and let $h: N \rightarrow N$ a diffeomorphism such that $h$ is smoothly isotopic to the identity map $\text{id}_N : N \rightarrow N$.
It's clair that the ...
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2answers
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What does it mean for a (non-smooth) homeomorphism between oriented smooth manifolds to be orientation preserving?
The definitions I know of orientability of manifolds are in terms of tangent spaces. However, for example in this answer there is mention of orientation preserving homeomophisms (between orientable ...
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2answers
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Fundamental group of $M$ has no subgroup of index $2\Rightarrow M$ is orientable
Let $M$ be a connected smooth manifold such that, for every $p\in M$, the fundamental group $\pi_1(M,p)$ has no subgroup of index $2$. Prove that $M$ is orientable.
Here's what I know: there is a ...
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2answers
29 views
Simple stokes - why is this the correct orientation?
We want to calculate $\iint_{S}\text{curl}(\vec F)dS$ where $\vec{F}(x,y,z)=(y^2z, xz,x^2y^2)$ and $S$ is the part of the paraboloid $z=x^2+y^2$ that's inside the cylinder $x^2+y^2= 1$ with an outward ...
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Does the Gauss-Bonnet theorem apply to non-orientable surfaces?
I found statements of the Gauss-Bonnet theorem here, here, here, here, here, here, here, and here. None of them require that the surface be orientable. However, Ted Shifrin claims in a comment to this ...
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1answer
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$df_x$ maps $N(S.X)$ isomorphically
This is actually just a linear algebra problem, but this text is taken from Guillemin and Pollack, Differential Topology on page 100.
Real Problem: Let $f: X \to Y$ be smooth, $S = f^{-1}(Z)$ where ...
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2answers
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Conditions for Matrix to be Product of Near-Identity Matrices
For $\epsilon > 0$, let $M_{\epsilon}$ be the family of $n$ x $n$ real matrices A such that $||$A$ - $I$_n|| < \epsilon$, where $|| \cdot ||$ is the standard operator norm. If $\epsilon$ is ...
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1answer
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If an orientation of a tree graph has no source vertices, must the in-degree of each vertex in said orientation be equal to one?
Given any polytree $T$ (any orientation of a tree graph) such that $\forall v\in V(T)(\text{indeg}(v)\neq 0)$ does this imply that $\forall v\in V(T)(\text{indeg}(v)=1)$? I'm pretty sure its true, but ...
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Maps between equivalence classes of vector bundles with and without orientation fixed at a point
I'm reading Hatcher's "Vector Bundles and K-Theory" and he says something that seems to be false.
Here is a screenshot of the part of the book in question.
He says that if we compare $Vect^n_0(S^k)$ ...
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Exponential map is orientation preserving
Let us define the map $f:\mathbb{R}\to \mathbb{S}^1$ by $x\to e^{2\pi i x}$. I want to prove that this map is an orientation-preserving map and also it's restriction on the unit interval has an ...
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How Euler angles change when we reverse direction of some axes
I looked at the other questions but couldn't find an answer for this particular question:
I have measured Euler angles of an object in one coordinate system and I need to use these data in another ...
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1answer
35 views
Relative orientation of satellite to a rotating plane.
We know the GPS position of a Geostationry satellite and a sensor. We also know the sensor orientation relative to the magnetic North of Earth. How do we find the orientation of Satellite relative to ...
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$M$ is orientable if and only if $M \setminus \{p\}$ is orientable.
Let $M$ a manifold of class $C^{\infty}$. Show that $M$ is orientable if and only if $M \setminus \{p\}$ is orientable.
Comments:
($\Rightarrow$) Let $\omega: M \longrightarrow \Lambda^n(M)$ a ...
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1answer
75 views
Direction of path depends on sign of determinant of Jacobian
Let $f: K_1(0) \rightarrow \mathbb{R}^2$ be continuously differentiable, $\{z_1,..,z_m\}=f^{-1}(a)$ with a regular $a \in \mathbb{R}^2$.
We choose $\epsilon$ small enough so that $f\vert_{\overline{U}...
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1answer
74 views
(Negative) Gradient and Orientability of its flow.
Before asking my question, I put the necessary definitions and some context. If you are used with Morse Theory, you can skip the text within [[[...]]].
[[[Let me first define what I mean by gradient ...
