Peer Reviewed Articles
367-370 Map Conversion and the UTM Grid
Frederick J. Doyle
Abstract
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Problems related to datum and coordinate conversion, Universal Transverse Mercator
(UTM) map grids, International Terrestrial Reference Frame (ITRF), and terrain
elevations derived from Global Positioning System (GPS) survey techniques
are reviewed in this paper, and the geometric foundation for coordinate systems
and map products are presented. Professional mapping societies must provide
education on these problems as related to the need to extend the utility
of the large scale maps of the United States into the 21st century. Mapping
agencies such as the USGS will be required to take steps necessary to insure
the currency of the 1:24 000-scale map series.
371-375 Datum Shifts for UTM Coordinates
R. Welch and A. Homsey
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The USGS 1:24 000-scale topographic maps and associated digital map products
of the United States are cast on the North American Datum of 1927 (NAD 27).
However, NAD 27 has been replaced by the North American Datum of 1983 (NAD
83). While shifts to translate the latitude/longitude (lat/long) graticule
coordinates to NAD 83 are documented, no information is readily available
on the shifts in metres needed to convert NAD 27 UTM Northing and Easting
grid coordinates to NAD 83 values. These shifts may be determined with computer
software such as the US Army Topographic Engineering Center (TEC) CORPSCON
package or the commercially available Blue Marble Geographics Geographic
Calculator program, and, when plotted at 2degrees intervals (lat/long) for
the contiguous 48 states, show a remarkable consistency within the 6-degree-wide
UTM zones, changing gradually from south to north. The shifts depicted in
the graphical plots provide the map user with the values needed to quickly
convert NAD 27 UTM grid coordinates to NAD 83 values.
377-380 The Gridded Map
Alden P. Colvocoresses
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Today, the most suitable coordinate referencing system for large- scale maps
is the Universal Transverse Mercator (UTM) grid. Most of the developed world
now uses the UTM (or its equivalent) grid on its larger-scale maps, but the
United States basic map series at 1:24 000 scale generally fails to do so.
The evolution of hand- held Global Positioning System (GPS) units capable
of delivering position accuracies to better than 10 m makes large-scale map
gridding an item of immediate concern. Proper and complete gridding of this
series should now be a top priority of the nation's mapping program.
381-383 Field Validation of the UTM Gridded Map
N.G. Terry, Jr.
Abstract
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Testing was conducted to evaluate the benefits of the UTM coordinate system
and a fully gridded map for land-navigation and coordinate measurement tasks.
Under field conditions, 20 of 22 test participants preferred the UTM coordinate
system to the latitude/longitude (lat/long) system, and all participants
favored maps with the full UTM grid to maps on which the grid is represented
as marginal tick marks. A full UTM grid allowed coordinates to be measured
quickly with a pocket-size coordinate reader to accuracies of approximately
10 m, as compared to 100 m when the map has only marginal UTM tick marks.
In order to facilitate the integrated use of maps with GPS and GIS technologies,
it is recommended that full UTM grids be printed on all 1:24 000-scale maps.
385-392 A Simulation Comparison of Three Marginal
Area Estimators for Image Classification
Ding Yuan
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Area estimations are often obtained through classifying surveyed or remotely
sensed data along with necessary adjustment. In this paper, three marginal
area estimators, including the direct estimator, inverse estimator, and additive
estimator for image classification, were compared using Monte Carlo simulations.
The results suggested that, under minimum constraints for the acceptable
image classifer and under our simulation environment: both inverse and direct
estimators were asymptotically unbiased and asymptotically zero-dispersed
as sampling fraction increased; the direct estimator normally has a smaller
bias than the inverse estimator, but the inverse estimator normally had smaller
dispersion than the direct estimator when the sampling fraction was small;
the additive estimator was not asymptotically unbiased and was competitive
with the other two methods only when sampling fraction and number of classes
were both small. Simulated feasible regions for the three marginal area estimators
are presented in this paper.
393-395 Quality Assessment of Polygon Labeling
Gerardo Bocco and Hugo Riemann
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The high costs in time and resources of data validation makes the correct selection
of a simple but robust adjustment method crucial. This paper describes an
approach suitable for a polygon labeling assessment. The approach uses the
geometric distribution where the sample size is a function of the desired
confidence level of the database. It allows the detailed random verification
of a selected map. All the area is equally exposed to testing and, if needed,
to correction.
397-402 Sensitivity of Selected Landscape Pattern
Metrics to Land-Cover Misclassification and Differences in Land-Cover Composition
James D. Wickham, Robert V. O'Neill, Kurt H. Riitters, Timothy G. Wade, and K.
Bruce Jones
Abstract
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Calculation of landscape metrics from land-cover data is becoming increasingly
common. Some studies have shown that these measurements are sensitive to
differences in land-cover composition, but none are known to have tested
also their sensitivity to land-cover misclassification. An error simulation
model was written to test the sensitivity of selected landscape pattern metrics
to misclassification, and regression analysis was used to determine if these
metrics were significantly related to differences in land-cover composition.
Comparison of sensitivity and regression results suggests that differences
in land-cover composition need to be about 5% greater than the misclassification
rate to be confident that differences in landscape metrics are not due to
misclassification.
403-414 Evaluating the Uncertainty of Area Estimates
Derived from Fuzzy Land-Cover Classification
Frank Canters
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The use of remotely sensed data as input into geographical information systems
has promoted new interest in issues related to the accuracy of multispectral
classification. This paper investigates the impact of classification uncertainty
on the estimation of area from satellite derived land-cover data. Applying
four variants of the maximum-likelihood classifier, it is shown that the
estimated area for different land-cover classes is highly influenced by the
methods which are used for classifier training. To evaluate the uncertainty
of area estimates, a new error modeling strategy is proposed. Assuming that
attribute uncertainty in image classification is field- based rather than
pixel-based, the image is segmented in fields according to similarities in
the probability vectors of adjacent pixels. In simulating uncertainty, this
field structure is explicitly taken into account. Using different strategies
for image segmentation, it is shown that the spatial correlation of classification
uncertainty has a major impact on the assessment of the uncertainty of area
estimates.
415-424 Effect of Database Errors on Intervisibility
Estimation
Ronald E. Huss and Mark A. Pumar
Abstract
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One of the most common uses of digital terrain databases is in the evaluation
of intervisibility, or clear line of sight, between points in space. These
evaluations are often used to make decisions regarding deployment of equipment
or personnel. However, there will be errors or discrepancies between the
database and the true terrain, and, because of these discrepancies, the visibility
in the field will differ from that predicted using the database. This paper
describes a method for calculating the probability of visibility over an
area for a given error specification. Results are described showing the sensitivity
of visibility uncertainty to database error and terrain roughness. Sensitivity
to other parameters is discussed. The results show that databases are very
good for predicting masking but are less reliable for predicting visibility.
Also, the reliability of the visibility predictions increases with increasing
terrain roughness.
425-434 Exploring and Evaluating the Consequences
of Vector-to-Raster and Raster-to-Vector Conversion
Russell G. Congalton
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Spatial data can be represented in two formats, raster (grid cell) or vector
(polygon). It is inevitable that conversion of the data between these two
formats be essential to the best use of the data. Most geographic information
systems (GIS) now provide software for such a conversion. The objective of
this study was to explore and evaluate the consequences of data conversion
on the accuracy of the resulting data layer. Simple shapes were chosen to
document the results of the raster-to- vector and vector-to-raster conversion
processes. These shapes included a square, a triangle (not aligned with the
grid), a circle, a hole within the circle, and a non-convex shape. Error
matrices were employed to represent the changes in area through the conversion
process. A second set of data including a circle, a thin rectangle, and a
wide rectangle were used to examine the effect of grid cell size on both
presence/absence of a feature as well as to maintain the feature's shape.
Finally, recommendations for continuing this work and its application to
information derived from remotely sensed data were presented.
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