What is the difference between true orthophoto and traditional orthophoto

Aerial images, due to the use of center projection, for the elevation of the building, will produce occlusion of the scene, according to the DEM out of the orthophoto, can not eliminate this occlusion phenomenon, which is the traditional orthophoto. This problem does not exist with true shot, the image of true shot looks like it is projected from directly above each object. If you want to produce a true orthophoto, there are very strict requirements from the external industry, the width of the air strip for each flight should be very narrow, the overlap should be large, and the internal data processing, the point cloud should be edited closely by hand to generate a DSM for orthophoto correction.

Comparing the correction method and building effect alone, the traditional DOM features are as follows:

Correction by DEM

It will produce tilted buildings

There will be occlusion caused by high-rise buildings

True DOM features are as follows:

Correction by DSM

Buildings are completely vertical, and any object in the picture looks down perpendicular to its direction

No occlusion