Flow measurement techniques determine velocity vector fields in liquid or gas flows. In fluid mechanics, many methods are based on seeding particles to visualize the flow imaged by an adequate camera system. The tomo-PIV (tomographic particle image velocimetry) technique presented in this paper generates time-resolved volumetric reconstructions of a particle constellation from a limited number of synchronized camera views. The advantage of tomo-PIV in contrast to the established 3-D PTV (particle tracking velocimetry) technique is its insensitivity to high seeding densities. While 3-D PTV comes with the necessity to detect, identify and match individual particles for establishing multi-image and multi-temporal correspondences, tomo-PIV facilitates volume-based tracking schemes applied to voxel cuboids filled with particles. The paper presents improved photogrammetric techniques for the determination of 3-D flow velocity fields. This includes a multi-camera system configuration and calibration, approaches for a full tomographic reconstruction in gas and liquid and 3-D least squares tracking for volume-based tracking in object space.