This research applies the semi-global matching (SGM) algorithm to generate high-quality urban digital surface models (UDSMs) with airborne oblique images. The oblique photogrammetry system (OPS) was influenced by and significantly affected photogrammetry. Thus

OPS can act as a good image source for generating high-quality UDSMs. UDSMs are more appealing than traditional DSMs to users due to the following advantages: 1) UDSMs comprehensively describe 3D urban surfaces. Therefore

inclined oblique images that are originally designed to determine the textures of overall buildings textures effectively solve the problem of the current DSM product involving space information loss at urban building facades. 2) Image matching and space interpretation are highly reliable in UDSMs. Similar targets

such as building roofs and floors

are often observed in multiple oblique stereo images with different title angles and baseline conditions. Thus

strong constraints based on redundant information can be used to either filter UDSM “noise” or remove false image matches effectively. 3) In UDSMs

the aerial solution to image occlusion is low-cost. Severe collisions usually occur among buildings in the aerial images of urban regions. The traditional solution to aerial photography occlusion involves increasing the degree of overlap among images at the cost of dense flights. This process ensures that the occlusion region is “visualized” in different images. The OPS itself considers the omnibearing observation of the urban scene; therefore

the occluded urban regions can be determined at minimal cost with this system. However

oblique image processing is challenging in terms of automation and quality. For instance

the stereo matching of oblique images is subject to various obstacles

such as significant illumination differences

severe occlusions

discontinuous object boundaries

and low or repetitive textures. To address such problems

a new approach is proposed based on the improved SGM algorithm and perspective projection-induced

multi-view UDSM fusion to generate UDSMs from airborne oblique images. The proposed approach is composed of two stages: 1) path-constrained SGM pyramid matching

in which the SGM algorithm is applied to oblique images that are subject to severe perspective distortion and long-range disparity search. To this end

reliable tie points from photogrammetry automatic triangulation (AAT) are used as unchanged “anchors” to block the propagation of SGM mistakes along the cost path. An effective initial disparity map is generated from these tie points through thin-plate spline transformation for implementing the pyramid version of SGM.2) Multi-view UDSM merging based on perspective occlusion judgment

where UDSM point clouds from the titular oblique view are projected onto the nadir image for occlusion judgment and overlap test. As a result

projected UDSMs are classified into occlusion

redundant

and non-redundant collections. A UDSM is obtained with complete space information by removing redundant point clouds from the titular oblique UDSMs and by merging the remaining point clouds with nadir UDSMs.Five airborne oblique stereo images are derived from OPS

and cameras are positioned in the configuration of a Maltese cross. The selected images are tested using the proposed approach to generate UDSMs for local urban regions. The proposed approach not only generated a dense disparity map for each oblique stereo image more effectively than the original SGM algorithm did

but the method also produced high-quality UDSMs that describe 3D urban surfaces more completely than traditional UDSMs.The following results are obtained: (1) the incorporation of constraints from reliable AAT tie points and the implementation of pyramid matching improve SGM performance with respect to the dense matching of airborne oblique images. In particular

this improvement is observed with regard to blocking the propagation of SGM mistakes along the cost path

reducing search range disparities

and saving on-line memory requirements. As a result

a high-quality disparity map can be produced at low computational cost. (2) As per the analysis of perspective projection

most building facades and occluded ground surfaces can be extracted automatically from four titled UDSMs. This process compensates for the deficiencies of nadir UDSMs while removing redundant point clouds simultaneously. As a result

high-quality UDSMs can be generated that describe 3D urban surfaces completely. These findings act as a foundation for actual orthoimage generation and 3D city modeling.