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\begin{document}

\title{Evaluation of Handheld Apple iPad Lidar for Measurements of Topography
and Geomorphic Change}



\author[1]{Peter Nelson}%
\affil[1]{Colorado State University}%


\vspace{-1em}



  
  \date{June 17, 2024}


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\begin{abstract}
High-resolution topographic data are used in geomorphic and hydrologic
research for many purposes, including topographic change detection,
development of computational meshes for hydraulic models, characterizing
channel and hillslope geometry, measuring vegetation structure and
density. These data can be collected in a variety of ways, ranging from
manual surveying with a Total Station or GPS system, airborne LiDAR,
terrestrial laser scanning (TLS), and Structure-from-Motion (SfM)
photogrammetry using images collected from drones or pole-mounted
cameras. These methods can be very time consuming to collect, and the
equipment they require can be very costly. With the release of the 2020
iPad Pro and iPhone 12 Pro, Apple added a LiDAR sensor to their devices,
enabling them to be used as hand-held 3D scanners. This new technology
has the potential to enable very rapid collection of high-resolution
topographic data at low cost. Here, we investigate how well iPad-based
LiDAR characterizes topography and topographic change in hillslope and
fluvial environments. A 2020 iPad Pro using two apps (3D Scanner and
Polycam) was used to collect topographic data over areas ranging from
about 100 -- 600 m\textsuperscript{2}. These same areas were scanned
with a Topcon GLS-2000 TLS system, and aerial imagery were collected
with a UAV and processed with Agisoft Metashape to create SfM point
clouds. Ground-based targets visible in the datasets were surveyed with
an RTK-GNSS system and used to register and scale the datasets. The
datasets were aligned using the ICP algorithm in CloudCompare, and
cross-sections and topographic differences were extracted from each
dataset and compared. Our analysis indicates that transects collected
with the iPad LiDAR have mean absolute differences with TLS and SfM data
within 3 cm, making these data comparable to other high-resolution
topographic data collection methods.%
\end{abstract}%



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