TIR images ordinarily have low-resolution and the contrast of the images is very low. The photogrammetric processing of thermal infrared (TIR) images deals with several difficulties.

Finally, as a conclusion, some open issues and future research directions are presented. In parallel, the processing of large image datasets has recently been accelerated by General-Purpose Graphics Processing Unit (GPGPU) approaches that are also summarized in this work.

Many challenges are currently being overcome by recent methods based on the reconstruction of multi-sensorial 3D scenarios. Surveyed applications are focused on agriculture and forestry since these fields concentrate most applications and are widely studied. This survey aims to present a summary of previous work according to the most relevant contributions for the reconstruction and analysis of 3D models of real scenarios using multispectral, thermal and hyperspectral imagery. In this scope, many approaches have been presented for 3D modeling, remote sensing, image processing and mapping, and multi-source data fusion. Recent studies focused on Earth observation and characterization are enhanced by the proliferation of Unmanned Aerial Vehicles (UAV) and sensors able to capture massive datasets with a high spatial resolution. This path is already being taken by the recent and fast-developing research in computational fields, however, some issues related to computationally expensive processes in the integration of multi-source sensing data remain. This will enable, among others, unsupervised automatic sampling of meaningful material classes from the target area for adaptive semi-supervised deep learning techniques. Three-dimensional (3D) image mapping of real-world scenarios has a great potential to provide the user with a more accurate scene understanding.

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