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Made charts have static methods, defined traits convention for tags.

release/4.3a0
Frank Dellaert 2014-12-04 22:01:14 +00:00
parent b5e3c8816d
commit 493b38ef28
1 changed files with 18 additions and 12 deletions
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30
GTSAM-Concepts.md
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@ -40,9 +40,8 @@ A given chart is implemented using a small class that defines the chart itself (
* types: * types:
* `Manifold`, a pointer back to the type * `Manifold`, a pointer back to the type
* valid expressions: * valid expressions:
* `Chart chart(p)` constructor * `v = Chart::local(p,q)`, the chart, from manifold to tangent space, think of it as *p (-) q*
* `v = chart.local(q)`, the chart, from manifold to tangent space, think of it as *p (-) q* * `p = Chart::retract(p,v)`, the inverse chart, from tangent space to manifold, think of it as *p (+) v*
* `p = chart.retract(v)`, the inverse chart, from tangent space to manifold, think of it as *p (+) v*
For many differential manifolds, an obvious mapping is the `exponential map`, which associates straight lines in the tangent space with geodesics on the manifold (and it's inverse, the log map). However, there are two cases in which we deviate from this: For many differential manifolds, an obvious mapping is the `exponential map`, which associates straight lines in the tangent space with geodesics on the manifold (and it's inverse, the log map). However, there are two cases in which we deviate from this:
@ -106,7 +105,7 @@ GTSAM Types start with Uppercase, e.g., `gtsam::Point2`, and are models of the T
Traits Traits
------ ------
We will not use Eigen-style or STL-style traits, that define *many* properties at once. Rather, we use boost::mpl style meta-programming functions to facilitate meta-programming, which return a single type or value for every trait. We will not use Eigen-style or STL-style traits, that define *many* properties at once. Rather, we use boost::mpl style meta-programming functions to facilitate meta-programming, which return a single type or value for every trait. Some rationale/history can be found [here](http://www.boost.org/doc/libs/1_55_0/libs/type_traits/doc/html/boost_typetraits/background.html).
Traits allow us to play with types that are outside GTSAM control, e.g., `Eigen::VectorXd`. However, for GTSAM types, it is perfectly acceptable (and even desired) to define associated types as internal types, as well, rather than having to use traits internally. Traits allow us to play with types that are outside GTSAM control, e.g., `Eigen::VectorXd`. However, for GTSAM types, it is perfectly acceptable (and even desired) to define associated types as internal types, as well, rather than having to use traits internally.
@ -145,6 +144,15 @@ The conventions for `gtsam::traits` are as follows:
By *inherting* the trait from the functor, we can just use the [currying](http://en.wikipedia.org/wiki/Currying) style `gtsam::traits::manhattan<Point2>℗(q)`. Note that, although technically a functor is a type, in spirit it is a free function and hence starts with a lowercase letter. By *inherting* the trait from the functor, we can just use the [currying](http://en.wikipedia.org/wiki/Currying) style `gtsam::traits::manhattan<Point2>℗(q)`. Note that, although technically a functor is a type, in spirit it is a free function and hence starts with a lowercase letter.
* Tags: `gtsam::traits::some_category<T>::type`, i.e., they are lower_case and define a *single* `type`, for example:
template<>
gtsam::traits::structure_category<Point2> {
typedef vector_space_tag type;
}
See below for the tags defined within GTSAM.
Tags Tags
---- ----
@ -155,14 +163,14 @@ Algebraic structure concepts are associated with the following tags
* `gtsam::traits::lie_group_tag` * `gtsam::traits::lie_group_tag`
* `gtsam::traits::vector_space_tag` * `gtsam::traits::vector_space_tag`
which should be queryable by `gtsam::traits::structure<T>` which should be queryable by `gtsam::traits::structure_category<T>::type`
The group composition operation can be of two flavors: The group composition operation can be of two flavors:
* `gtsam::traits::additive_group_tag` * `gtsam::traits::additive_group_tag`
* `gtsam::traits::multiplicative_group_tag` * `gtsam::traits::multiplicative_group_tag`
which should be queryable by `gtsam::traits::group_flavor<T>::tag` which should be queryable by `gtsam::traits::group_flavor<T>::type`
Manifold Example Manifold Example
@ -176,9 +184,8 @@ An example of implementing a Manifold type is here:
class Rot2 { class Rot2 {
typedef Vector2 TangentVector; typedef Vector2 TangentVector;
class Chart { class Chart {
Chart(const Rot2& R); static TangentVector local(const Rot2& R1, const Rot2& R2);
TangentVector local(const Rot2& R) const; static Rot2 retract(const Rot2& R, const TangentVector& v);
Rot2 retract(const TangentVector& v) const;
} }
Rot2 operator*(const Rot2&) const; Rot2 operator*(const Rot2&) const;
Rot2 transpose() const; Rot2 transpose() const;
@ -254,9 +261,8 @@ Providing the Vector space concept is easier:
Point2 operator-() const; Point2 operator-() const;
// Still needs to be defined, unless Point2 *is* Vector2 // Still needs to be defined, unless Point2 *is* Vector2
class Chart { class Chart {
Chart(const Rot2& R); static Vector2 local(const Point2& p, const Point2& q) const;
Vector2 local(const Rot2& R) const; static Rot2 retract(const Point2& p, const Point2& v) const;
Rot2 retract(const Vector2& v) const;
} }
} }
``` ```