This paper introduces a disparity-independent framework for 3D localization in heterogeneous stereo vision systems. Unlike conventional disparity-based approaches, the method employs independent monocular calibration, cooperative geometric projection, and polynomial focal length fitting with integrated error compensation to directly compute spatial coordinates. This reformulation reduces the reconstruction problem to a constant-time linear algebra solution, achieving real-time efficiency. The framework accommodates variations in focal length, installation height, and tilt angle, thereby overcoming the homogeneous camera assumption. Extensive experiments under diverse configurations demonstrate an average accuracy of 97.9%, substantially outperforming SGBM, PSMNet, and RAFT-Stereo. The proposed method exhibits strong robustness to camera heterogeneity and environmental perturbations, making it suitable for robotic applications requiring cost-effective, high-precision localization in dynamic and resource-constrained settings.