Spatial Grid Based Detection With Implicit Anchor Free Localization

via “single-stage detector with anchor-free and anchor-based variants”

OpenMMLab detection toolbox with 300+ models.

Unique: Provides both anchor-based (RetinaNet, ATSS) and anchor-free (FCOS, CenterNet) single-stage detectors with unified training pipeline, allowing direct comparison of approaches; uses focal loss to address class imbalance without hard negative mining, enabling end-to-end training

vs others: Faster inference than two-stage detectors (Faster R-CNN) with comparable accuracy on large objects; more flexible than YOLO because anchor aspect ratios and scales are configurable per dataset; better documented than EfficientDet with 300+ pre-trained checkpoints across architectures