DOI: 10.5880/crc1211db.69
title: High resolution Digital Terrain Models (DTM) of Tillandsiales in the Chilean Atacama Desert: The Caldera study field

description: A high-resolution Digital Terrain Model (DTM) has been processed for the Tillandsia landbeckii study sites at Arica. The original source data have been obtained from drone flight images. The final resolution of the DTM is of about 16 cm/px. We acknowledge support in the field and during data processing from Alexander Siegmund (PH Heidelberg).
description: The zip.file contains the following 5 files: 
1) Caldera.blend 
2) Caldera_Ortho_0-5res_clipped.tif 
3) Caldera_DEM_clipped_rescale.tif 
4) Caldera_DEM_clipped_rescale_0-5res.tif 
5) Caldera_DEM_clipped_rescale_0-5res_rendered.tif 
Please do not change file names nor file extensions when loading files for viewing in BLENDER version 4.0 (https://www.blender.org/download/releases/4-0/).
The "0-5res" file-versions refer to a 0.5m/px resolution (EPSG:32719 - WGS 84 / UTM Zone 19S). File Caldera_DEM_clipped_rescale.tif was processed to a final resolution of 1.67e-06 °degrees (c. 0.165 m) [EPSG:4326 - WGS 84].
description: Short introduction into the methods: Very-high resolution images were captured using an unmanned aerial vehicle (UAVs) [drone: DJI Matrice 200; DJI Zenmuse X5S RGB camera]. With processing of the UAV data images are merged according to their geographical position by means of the Structure-from-Motion (SfM) algorithm and a digital elevation model was created (Micheletti et al. 2015; Westoby et al. 2012). High-resolution topographic surveying using the Structure-from-Motion (SfM) algorithm is a low-cost and user-friendly photogrammetric technique to obtain high-resolution datasets. The SfM method solves the camera pose and scene geometry simultaneously and automatically, using highly redundant bundle adjustment based on matching features in multiple overlapping, offset images (Westoby et al. 2012). SfM-Processing was performed using Agisoft Metashape Professional (Version 1.6.1 64 bit). Agisoft Metashape Professional performs well to reconstruct landscape 3D point clouds and the different steps of the process are configurable and can be controlled (Laporte-Fauret et al. 2019). Images were fed into the software and the quality (tool “estimate image quality”) and position was determined respectives images were chosen to cover the study area. Using the “Aling Photos” tool images were aligned creating tie points (2D) and a Depth Maps (high quality, mild filtering) was created (3D). With the help of the Build Dense Cloud tool, set to high quality, the data points were created that represent the study area in 3D. Consecutively an orthomosaic of the study area was created using the Build Orthomosaic tool. An orthomosaic is a photogrammetrically orthorectified image product that has been mosaicked from a collection of images and corrected for geometric distortion to create a seamless mosaic dataset. Due to the high-resolution input data and the processing without compression a high-resolution orthomosaic was achieved with a pixel size of 2.1 cm/pix covering the study area. This detailed, high-resolution geolocated photo representation of the study site is the basis for the following analytical steps. A digital elevation model (DEM) was computed using the “Build DEM” tool. Its dimensions resulted herein in a 16.5 cm/pix size to cover the entire study site. Final adjustment of elevation has been done using the Copernicus Digital Elevation Model (https://spacedata.copernicus.eu/de/collections/copernicus-digital-elevation-model) using QGIS (https://www.qgis.org/de/site/). Laporte-Fauret, Q., et al. (2019). "Low-Cost UAV for high-resolution and large-scale coastal dune change monitoring using photogrammetry." Journal of Marine Science and Engineering 7(3): 63. Micheletti, N., Chandler, J. H., & Lane, S. N. (2015). Structure from motion (SFM) photogrammetry. In L. E. Clarke, & J. M. Nield (Eds.), Geomorphological techniques (Online Edition) (pp. 1–12, Chapter 2.2.2). British Society for Geomorphology Westoby, M. J., et al. (2012). "‘Structure-from-Motion’photogrammetry: A low-cost, effective tool for geoscience applications." Geomorphology 179: 300-314.