Shadow Orientation Research Articles

Detection and Classification of Buildings by Height from Single Urban High-Resolution Remote Sensing Images

Recent improvements in remote sensing technologies have boosted building detection techniques from rough classifications using moderate resolution imagery to precise extraction from high-resolution imagery. Shadows frequently emerge in high-resolution urban images. To exploit shadow information, we developed a novel building detection and classification algorithm for images of urban areas with large-size shadows, employing only the visible spectral bands to determine the height levels of buildings. The proposed method, building general-classified by height (BGCH), calculates shadow orientation, detects buildings using seed-blocks, and classifies the buildings into different height groups. Our proposed approach was tested on complex urban scenes from Toronto and Beijing. The experimental results illustrate that our proposed method accurately and efficiently detects and classifies buildings by their height levels; the building detection rate exceeded 95%. The precision of classification by height levels was over 90%. This novel building-height-level detection method provides rich information at low cost and is suitable for further city scene analysis, flood disaster risk assessment, population estimation, and building change detection applications.

Determining True North on Mars by Using a Sundial on InSight

In this work, we demonstrate the possibility to determine the true North direction on Mars by using a gnomon on the InSight mission. The Sun local coordinates are computed using the analytical solution VSOP87 for the planetary ephemeris. The Sun position in the sky induce specific gnomon shadow orientation and length that can be read on a target. By comparing the images of the shadow with the expected position of the Sun, we can determine the true North direction with an accuracy up to $1^{\circ }$ , well within the seismic requirement of $5^{\circ }$ , even if the lander position or the gnomon verticality are not accurate. To achieve this result, we determine the best periods of observation during the SEIS deployment phase in December 2018. A total period of 5 hours has been identified on mornings and evenings on Mars, during which the impact of errors on position and verticality on the true North direction are minimised.

Facilitating Preschoolers’ Scientific Knowledge Construction via Computer Games Regarding Light and Shadow: The Effect of the Prediction-Observation-Explanation (POE) Strategy

Educational researchers have suggested that computer games have a profound influence on students’ motivation, knowledge construction, and learning performance, but little empirical research has targeted preschoolers. Thus, the purpose of the present study was to investigate the effects of implementing a computer game that integrates the prediction-observation-explanation (POE) strategy (White and Gunstone in Probing understanding. Routledge, New York, 1992) on facilitating preschoolers’ acquisition of scientific concepts regarding light and shadow. The children’s alternative conceptions were explored as well. Fifty participants were randomly assigned into either an experimental group that played a computer game integrating the POE model or a control group that played a non-POE computer game. By assessing the students’ conceptual understanding through interviews, this study revealed that the students in the experimental group significantly outperformed their counterparts in the concepts regarding “shadow formation in daylight” and “shadow orientation.” However, children in both groups, after playing the games, still expressed some alternative conceptions such as “Shadows always appear behind a person” and “Shadows should be on the same side as the sun.”

Search for gross illumination discrepancies in images of natural objects

Shadows may be "discounted" in human visual perception because they do not provide stable, lighting-invariant, information about the properties of objects in the environment. Using visual search, R. A. Rensink and P. Cavanagh (2004) found that search for an upright discrepant shadow was less efficient than for an inverted one. Here we replicate and extend this work using photographs of real objects (pebbles) and their shadows. The orientation of the target shadows was varied between 30 and 180 degrees. Stimuli were presented upright (light from above, the usual situation in the world) or inverted (light from below, unnatural lighting). RTs for upright images were slower for shadows angled at 30 degrees, exactly as found by Rensink and Cavanagh. However, for all other shadow angles tested, the RTs were faster for upright images. This suggests, for small discrepancies in shadow orientation, a switch of processing from a relatively coarse-scaled shadow system to other general-purpose visual routines. Manipulations of the visual heterogeneity of the pebbles that cast the shadows differentially influenced performance. For inverted images, heterogeneity had the expected influence: reducing search efficiency and increasing overall search time. This effect was greatly reduced when images were presented upright, presumably when the distractors were processed as shadows. We suggest that shadows may be processed in a functionally separate, spatially coarse, mechanism. The pattern of results suggests that human vision does not use a shadow-suppressing system in search tasks.

Shadows: Young Taiwanese children’s views and understanding

The purpose of this study was to examine young children’s views about shadows. Young children hear references to or are involved in many scientific experiences in their everyday lives, and shadows are a part of children’s everyday experiences. Young children may have constructed their knowledge about shadows through their daily experiences. Therefore, a total of 32 children, of which one‐half were four years old and one‐half were five years old, were individually interviewed twice to elicit their views and understanding of shadows. Data were collected by a mixture of picture‐pointing, verbal explanation, and manipulation, and were analysed both quantitatively and qualitatively. We focused on five facets of children’s ideas about shadows: ideas about the source of light, shadow orientation, shadow shape, shadow size, and shadow intensity. The five year olds performed significantly better on production of shadows, production of shadow shape, and production of shadow size, and also gave more reasonable explanations for their choices than did the four year olds, showing a better understanding of the concept of shadows. Another significant finding of the study was that young children have a much more sophisticated understanding of shadows than Piaget originally suggested and than their verbal explanations imply.

Pressure shadows and relative movements in a shear zone

The determination of direction‐sense of movement by means of pressure shadow orientation has been investigated by MÜGGE [1930] in some detail. As far as the writer knows, no correlation of this deduced direction‐sense with a field example of relative movement has previously been made. Study of an oriented specimen taken from the Campbell shear zone at Yellowknife (N. W. T., Canada), where the direction‐sense of movement has been established with reasonable certainty, now provides this correlation. Interpretation of the pressure shadow orientation around pyrite grains in the rock confirms the field data in every way. It would seem that this structure warrants closer attention and application than it has received heretofore.