TransferEdges - GTSAM Docs

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Resolve the shared target view and matrix orientations for transfer factors.

Authors: Frank Dellaert, et al. (see THANKS for the full author list)

See LICENSE for the license information

Mathematical idea¶

An epipolar matrix reverses orientation by transposition: if $F_{ij}$ maps a point in view $i$ to a line in view $j$ , then

F_{ji}=F_{ij}^{\mathsf T}.

(1)

TransferEdges finds the shared target view $c$ and orients both stored matrices so they produce lines in that same view before a transfer factor intersects them.

try:
    import google.colab
    %pip install --quiet gtsam-develop
except ImportError:
    pass

import gtsam
import numpy as np

from gtsam import symbol_shorthand

C = symbol_shorthand.C
K = symbol_shorthand.K
P = symbol_shorthand.P
S = symbol_shorthand.S
X = symbol_shorthand.X

Purpose and availability¶

TransferEdges<F> is a public C++ helper base used by the transfer-factor family. Given edges (a,c) and (b,c) in either orientation, it finds views a, b, and shared target c, then transposes matrices as needed so both map into view c.

It is not exposed as a standalone Python class; Python users configure it indirectly through a transfer-factor constructor.

C++ example¶

#include <gtsam/sfm/TransferFactor.h>

using namespace gtsam;

const EdgeKey edgeAC(0, 2);
const EdgeKey edgeCB(2, 1);  // reversed relative to (b, c)

const size_t a = TransferEdges<FundamentalMatrix>::ViewA(edgeAC, edgeCB);
const size_t b = TransferEdges<FundamentalMatrix>::ViewB(edgeAC, edgeCB);
const size_t c = TransferEdges<FundamentalMatrix>::ViewC(edgeAC, edgeCB);
// a == 0, b == 1, c == 2

The edges must share exactly the intended target view. Disjoint edges throw at construction.

Source¶

TransferFactor.h