CameraTransform: A Python package for perspective corrections and image mapping

Gerum, Richard; Richter, Sebastian; Winterl, Alexander; Mark, Christoph; Fabry, Ben; Bohec, Céline Le; Zitterbart, Daniel P.

doi:10.1016/j.softx.2019.100333

Cited by 26 publications

(31 citation statements)

References 19 publications

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“…R rs values were used as input into optical algorithms derived from the best performing multiple linear regressions and mean chlorophyll a and TSS concentration at each station was obtained by averaging values across all images. The resulting arrays were georeferenced using the Python libraries "CameraTransform" (Gerum et al, 2019) and "Rasterio" using archived metadata including latitude, longitude, image width, image height to position the images accurately in a known coordinate system (WGS84). Georeferenced arrays were exported as individual TIFFs and mapped using ArcGIS Pro (ESRI Inc. Redlands, CA, United States).…”

Section: Removal Of Surface Reflected Light (L Sr )mentioning

confidence: 99%

Evaluation of Unoccupied Aircraft System (UAS) Remote Sensing Reflectance Retrievals for Water Quality Monitoring in Coastal Waters

Windle

Silsbe

2021

Front. Environ. Sci.

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Unoccupied aircraft systems (UAS, or drones) equipped with off-the-shelf multispectral sensors originally designed for terrestrial applications can also be used to derive water quality properties in coastal waters. The at-sensor total radiance a UAS measured constitutes the sum of water-leaving radiance (LW) and incident radiance reflected off the sea surface into the detector’s field of view (LSR). LW is radiance that emanates from the water and contains a spectral shape and magnitude governed by optically active water constituents interacting with downwelling irradiance while LSR is independent of water constituents and is instead governed by a given sea-state surface reflecting light; a familiar example is sun glint. Failure to accurately account for LSR can significantly influence Rrs, resulting in inaccurate water quality estimates once algorithms are applied. The objective of this paper is to evaluate the efficacy of methods that remove LSR from total UAS radiance measurements in order to derive more accurate remotely sensed retrievals of scientifically valuable in-water constituents. UAS derived radiometric measurements are evaluated against in situ hyperspectral Rrs measurements to determine the best performing method of estimating and removing surface reflected light and derived water quality estimates. It is recommended to use a pixel-based approach that exploits the high absorption of water at NIR wavelengths to estimate and remove LSR. Multiple linear regressions applied to UAS derived Rrs measurements and in situ chlorophyll a and total suspended solid concentrations resulted in 37 and 9% relative error, respectively, which is comparable to coastal water quality algorithms found in the literature. Future research could account for the high resolution and multi-angular aspect of LSR by using a combination of photogrammetry and radiometry techniques. Management implications from this research include improved water quality monitoring of coastal and inland water bodies in order to effectively track trends, identify and mitigate pollution sources, and discern potential human health risks.

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Section: Removal Of Surface Reflected Light (L Sr )mentioning

confidence: 99%

Evaluation of Unoccupied Aircraft System (UAS) Remote Sensing Reflectance Retrievals for Water Quality Monitoring in Coastal Waters

Windle

Silsbe

2021

Front. Environ. Sci.

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“…To correct for perspective distortions, we calculate the area represented by one pixel depending on its vertical (y-) position in the image. The calculation is based on the projection specified by the intrinsic and extrinsic camera matrix (Supplementary Figure S2, Gerum et al 2017b). The colony area is then calculated as the perspective-corrected area of the pixels belonging to the K-means group with the lowest intensity.…”

Section: Methodsmentioning

confidence: 99%

Phase transitions in huddling emperor penguins

Richter

Gerum

Winterl

et al. 2018

J. Phys. D: Appl. Phys.

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Emperor penguins (Aptenodytes forsteri) are highly adapted to the harsh conditions of the Antarctic winter: they are able to fast for up to 134 days during breeding. To conserve energy, emperor penguins form tight groups (huddles), which is key for their reproductive success. The effect of different meteorological factors on the huddling behaviour, however, is not well understood. Using time-lapse image recordings of an emperor penguin colony, we show that huddling can be described as a phase transition from a fluid to a solid state. We use the colony density as order parameter, and an apparent temperature that is perceived by the penguins as the thermodynamic variable. We approximate the apparent temperature as a linear combination of four meteorological parameters: ambient temperature, wind speed, global radiation and relative humidity. We find a wind chill factor of −2.9 °C/(ms−1), a humidity chill factor of −0.5°C/% rel. humidity, and a solar radiation heating factor of 0.3 °C//(Wm2). In the absence of wind, humidity and solar radiation, the phase transition temperature (50% huddling probability) is −48.2°C for the investigated time period (May 2014). We propose that higher phase transition temperatures indicate a shrinking thermal insulation and thus can serve as a proxy for lower energy reserves of the colony, integrating pre-breeding foraging success at sea and energy expenditure at land due to environmental conditions. As current global change is predicted to have strong detrimental effects on emperor penguins within the next decades, our approach may thus contribute towards an urgently needed long-term monitoring system for assessing colony health.

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“…When two adults are closer than 0.45 m, they are classified as pairs, as discussed below. Correction for the camera perspective is performed by affine image transformation with a transformation matrix that we obtain from point correspondences of prominent landscape features (buildings, walls) seen in Google Maps satellite images of the region [12].…”

Section: Methodsmentioning

confidence: 99%

Structural organisation and dynamics in king penguin colonies

Gerum¹,

Richter²,

Fabry³

et al. 2018

J. Phys. D: Appl. Phys.

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During breeding, king penguins do not build nests, however they show strong territorial behaviour and keep a pecking distance to neighbouring penguins. Penguin positions in breeding colonies are highly stable over weeks and appear regularly spaced, but thus far no quantitative analysis of the structural order inside a colony has been performed. In this study, we use the radial distribution function to analyse the spatial coordinates of penguin positions. Coordinates are obtained from aerial images of two colonies that were observed for several years. Our data demonstrate that the structural order in king penguin colonies resembles a 2-dimensional liquid of particles with a Lennard-Jones-type interaction potential. We verify this using a molecular dynamics simulation with thermally driven particles, whereby temperature corresponds to penguin movements, the energy well depth e of the attractive potential corresponds to the strength of the colony-forming behaviour, and the repulsive zone corresponds to the pecking radius. We can recapitulate the liquid disorder of the colony, as measured by the radial distribution function, when the particles have a temperature of several (1.4-10) ε/kB and a normally distributed repulsive radius. To account for the observation that penguin positions are stable over the entire breeding period, we hypothesize that the liquid disorder is quenched during the colony formation process. Quenching requires the temperature to fall considerably below 1 ε/kB, which corresponds to a glass transition, or the repulsion radius to exceed the distance between neighbouring penguins, which corresponds to a jamming transition. Video recordings of a breeding colony together with simulations suggest that quenching is achieved by a behavioural motility arrest akin to a glass transition. We suggest that a liquid disordered colony structure provides an ideal compromise between high density and high flexibility to respond to external disturbances that require a repositioning of penguins.

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CameraTransform: A Python package for perspective corrections and image mapping

Cited by 26 publications

References 19 publications

Evaluation of Unoccupied Aircraft System (UAS) Remote Sensing Reflectance Retrievals for Water Quality Monitoring in Coastal Waters

Evaluation of Unoccupied Aircraft System (UAS) Remote Sensing Reflectance Retrievals for Water Quality Monitoring in Coastal Waters

Phase transitions in huddling emperor penguins

Structural organisation and dynamics in king penguin colonies

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