CaGIS vol. 35, no. 3 (July 2008)

Modeling the Potential Swath Coverage of Nadir and Off-Nadir Pointable Remote Sensing Satellite-Sensor Systems

Michael E. Hodgson and Bandana Kar

Pointable sensor systems onboard many earth resources satellites today, particularly the higher spatial resolution sensors, provide for a near infinite set of collection opportunities. Satellite orbits of these systems are not systematic repetitive tracks. Predicting future collection opportunities requires predicting where the satellite will be and then computing the potential swath coverage from a pointable sensor along these orbits. While each agency or company models its own satellite-sensor systems, few publicly available sources exist for mapping future satellite ground tracks. Evaluating collection opportunities from multiple satellite-sensor systems from different agencies/companies is problematic. The purpose of the research described in this article was to develop a generic approach for modeling future satellite-sensor collection opportunities. In this article, formulae are developed for computing the potential swath coverage, and an algorithm is designed for constructing the potential swath coverage area. The solution to the swath coverage problem is based on spherical trigonometry, a well known map projection (i.e., azimuthal equidistant map projection) used in an unconventional dynamic form, and a satellite orbital propagation model. We demonstrate how the computation of the swath coverage area can be accomplished using a temporal series of re-centered map projections.

Equations of the Mayr Projection

Cengizhan Ipbuker

In this study, the pseudo-cylindrical projection of Franz Mayr is examined in detail. The computation of one of Mayr’s projection equations depends on the solution of an elliptical integral. It is this characteristic of the projection that most likely contributes to it being the neglected one among the group of the pseudo-cylindrical projections available today. Franz Mayr used the Legendre tables for the elliptical functions E and F and gave the plane coordinates within one-degree latitude intervals on the 90°meridian. The research reported here derives analytical expressions instead of using the elliptical integral and the interpolation between the table values. Four different solutions have been introduced for mapping applications. The distortion quantities are also presented and discussed.

KEYWORDS: Equal-area pseudo-cylindrical projections, Mayr projection, elliptic integral

Explaining Map-reading Performance Efficiency: Gender, Memory, and Geographic Information

Robert Earl Lloyd and Rick L. Bunch

This paper explains the performance of a map-reading task that required subjects to locate a state on a map of the United States after being given the state’s name. Response times and accuracy were hypothesized to be a function of differences among the decision makers and among the states. The cognitive science literature suggests that variation in performance can be explained by the interaction of biological and environmental variables. Individual differences in gender, working memory capacity, and brain lateralization were hypothesized to affect performance of the spatial task. Results indicated gender could be a more informative variable than sex. Subjects, who identified with both feminine and masculine characteristics, had the fastest mean response times. Subjects, who did not identify with feminine or masculine characteristics, had the most accurate responses. Subjects who combined higher verbal and spatial working memory capacities had both the fastest and most accurate performances. The results supported other studies indicating a non-linear relationship relating sex, brain lateralization, and accuracy. Covariates related to gravity model variables were also significantly related to performance.

Keywords: Map-reading task, geographic information, brain lateralization, gender, and memory capacity

Expanding Display Size and Resolution for Viewing Geospatial Data: A User Study with Multiple-Monitor High-Resolution Displays

Candice R. Luebbering, Laurence  W. Carstensen, James B. Campbell, and Lawrence S. Grossman

Multiple-monitor configurations provide attainable, low-cost ways to create large, high-resolution displays. Increased screen space is particularly useful for viewing and interpreting rich, complex geospatial datasets, as both context and amount of detail can be simultaneously increased. To explore the utility of increasing display size and resolution for viewing geospatial data, this experiment required 57 subjects to perform map and image reading tasks using raster and vector data on one of three different monitor configurations: one (1280 × 1024 pixels), four (2560 × 2048 pixels), and nine (3840 × 3072 pixels). A computer program captured subject performance by recording answers, mouse-click locations, viewing areas, tool usage, and elapsed time. A post-experiment questionnaire obtained additional qualitative feedback about subjects’ testing experiences. Overall, subjects performed more efficiently on the larger display configurations, as evidenced by a reduction in completion time and in virtual navigation (mouse clicks) used to finish the test. Tool usage also differed among monitor conditions, with navigation tools dominating on the single monitor and  selection tools (tools used to provide answers) dominating on the nine-monitor display. Although overall results indicated the effectiveness of larger displays, task-level analyses showed that performance varied considerably from task to task.

End of file