**PixLoc** is a scene-agnostic neural network that estimates an accurate 6-DoF pose from an image and a 3D model. It is based on the direct alignment of multiscale deep features, casting camera localization as metric learning. PixLoc learns strong data priors by end-to-end training from pixels to pose and exhibits exceptional generalization to new scenes by separating model parameters and scene geometry. As the CNN never sees 3D points, PixLoc can generalize to any 3D structure available. This includes sparse SfM point clouds, dense depth maps from stereo or RGBD sensors, meshes, Lidar scans, but also lines and other primitives.

This paper introduces the fast adaptive stochastic function accelerator (FASFA) for gradient-based optimization of stochastic objective functions. It works based on Nesterov-enhanced first and second momentum estimates. The method is simple and effective during implementation because it has intuitive/familiar hyperparameterization. The training dynamics can be progressive or conservative depending on the decay rate sum. It works well with a low learning rate and mini batch size. Experiments and statistics showed convincing evidence that FASFA could be an ideal candidate for optimizing stochastic objective functions, particularly those generated by multilayer perceptrons with convolution and dropout layers. In addition, the convergence properties and regret bound provide results aligning with the online convex optimization framework. In a first of its kind, FASFA addresses the growing need for diverse optimizers by providing next-generation training dynamics for artificial intelligence algorithms. Future experiments could modify FASFA based on the infinity norm.

FASFA

PixLoc

Back to the Feature: Learning Robust Camera Localization from Pixels to Pose

Multi-layer neural networks traditionally use  dot products between the output vector of previous layer and the incoming weight vector as the input to activation function. The result of dot product is unbounded. To bound dot product and decrease the variance, **Cosine Normalization** uses cosine similarity or centered cosine similarity (Pearson Correlation Coefficient) instead of dot products in neural networks. 

Using cosine normalization, the output of a hidden unit is computed by:

$$o = f(net_{norm})= f(\cos \theta) = f(\frac{\vec{w} \cdot \vec{x}} {\left|\vec{w}\right|  \left|\vec{x}\right|})$$

where $net_{norm}$ is the normalized pre-activation,  $\vec{w}$ is the incoming weight vector and $\vec{x}$ is the input vector, ($\cdot$) indicates dot product, $f$ is nonlinear activation function. Cosine normalization bounds the pre-activation between -1 and 1.

Source	Back to the Feature: Learning Robust Camera Localization from Pixels to Pose
Year	2000
Data Source	CC BY-SA - https://paperswithcode.com