Rotation Averaging and Strong Duality 阅读

本文探讨了结构从运动(Structure from Motion)中涉及的技术,包括四元数和旋转矩阵等核心概念。这些数学工具在计算机视觉和三维重建中扮演着重要角色。

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This problem normally comes together with structure from motion: quarternions, rontation matrices and so on.

### Cell-Averaging CFAR Algorithm Implementation and Explanation In radar signal processing, the cell-averaging constant false alarm rate (CA-CFAR) technique is widely used to detect targets while maintaining a consistent probability of false alarms across varying noise levels. The CA-CFAR method operates by comparing the amplitude of each range cell under test with an adaptive threshold determined from neighboring cells. The core principle involves selecting guard cells immediately adjacent to the cell under test that are not included in averaging operations because these may be contaminated by target returns. Reference cells surrounding the guard region provide estimates of background clutter level which helps set detection thresholds dynamically based on local conditions[^1]. A typical implementation process includes: #### Step-by-step Process Description Given input data as a sequence representing received signals over time or space intervals called "range bins": 1. Define parameters including number of reference cells before (`N_before`) and after (`N_after`), plus any optional guard bands around the CUT. 2. For every potential target location within this dataset: * Calculate mean value using only valid references outside protected zones. * Apply scaling factor derived empirically according to desired Pfa (probability of false alarm). 3. Compare current sample against computed decision boundary; flag detections accordingly. Below demonstrates Python code implementing basic functionality described above: ```python import numpy as np def ca_cfar(signal, N_before=8, N_after=7, scale_factor=4.5): """ Perform Cell Averaging Constant False Alarm Rate Processing Args: signal (array): Input array containing complex IQ samples N_before (int): Number of leading edge reference cells N_after (int): Trailing edge count for same purpose scale_factor (float): Multiplier applied during threshold calculation Returns: detected_targets (list[int]): Indices where peaks exceed calculated limits """ num_samples = len(signal) window_size = N_before + 1 + N_after half_window = int((window_size - 1)/2) # Initialize output list storing indices corresponding to detected objects detected_targets = [] for i in range(half_window, num_samples-half_window): # Extract relevant subset excluding central element being evaluated now ref_cells = np.concatenate([ abs(signal[i-N_before:i]), abs(signal)[i+1:i+N_after+1]]) avg_power = np.mean(ref_cells) thresh = avg_power * scale_factor if abs(signal[i]) >= thresh: detected_targets.append(i) return detected_targets ``` This function takes into account both preceding and succeeding elements relative to each point along the series when computing average power measurements. By adjusting `scale_factor`, one can control sensitivity effectively without altering underlying logic structure significantly. --related questions-- 1. How does changing the size of reference windows impact performance metrics like PD (detection probability)? 2. What modifications would improve robustness towards non-Gaussian distributed interference? 3. Can you explain how log-domain computations benefit numerical stability compared to linear domain alternatives? 4. Are there alternative approaches beyond simple moving averages worth exploring for setting dynamic thresholds?
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