Raster Operations Research Articles

Topology in Raster and Vector Representation

Egenhofer’s nine-intersection, well-known for vector representations, is defined here on a raster, using a hybrid raster model, and then systematically transformed to yield functions which can be used in a convolution operation applied to a regular raster representation. Applying functions, the hybrid raster elements need not be stored. It becomes thus possible to determine the topological relation of two regions, given in raster representation, with the same reasoning as in vector representations. This contributes to the merging of raster and vector operations. It demonstrates how the same conceptual operations can be used for both representations, thus hiding in one more instance the difference between them.

Derivation of topographic variables from a digital elevation model given by a spheroidal trapezoidal grid

Digital elevation models (DEMs) given by spheroidal trapezoidal grids are more appropriate for large regional, sub-continental, continental and global geological and soil studies than square-spaced DEMs. Here we develop a method for derivation of topographic variables, specifically horizontal (k) and vertical h (k) landsurface curvatures, from spheroidal trapezoidal-spaced DEMs. First, we v derive equations for calculation of partial derivatives of elevation with DEMs of this sort. Second, we produce formulae for estimation of the method accuracy in terms of root mean square errors of partial derivatives of elevation, as well as k h and k (m and m respectively). We design the method for the case that the v kh k v Earth's shape can be ignored, that is, for DEM grid sizes of no more than 225 km. We test the method by the example of fault recognition using a DEM of a part of Central Eurasia. A comparative analysis of test results and factual geological data demonstrates that the method actually works in regions marked by complicated topographic and tectonic conditions. Upon increasing DEM grid size, one can produce generalised maps of k and k. Spatial distributions of m and m h v kh k v depend directly on the distribution of elevation RMSE. Areas with high values of m are marked by low values of m, and vice versa, areas with high values kh k v of m are marked by low values of m. Data on m and m should be utilised k v kh kh k v to control and improve applications of k and k to geological studies. The method h v developed opens up new avenues for carrying out some 'conventional' raster operations directly on geographical co-ordinates.

Teaching Raster GIS Operations with Spreadsheets

Many universities are introducing courses to teach students the principles of geographic information systems (GIS). In addition to lectures, exercises with commercial GIS software are offered to show basic operations. Although students learn to execute such operations, the software may hide their internal structure and logic. We propose using a spreadsheet program as a teaching tool for raster operations such as filter and overlay. Spreadsheets offer a practical way to demonstrate and experiment with raster operations, because the raster structure is captured in the form of rows and columns. With this tool, students are able to perform and visualize operations as well as to see how the data are processed by the algorithms. Our approach is new in that we concentrate on the algorithms of operations. We make explicit which raster functions are actually evaluated when performing a particular operation. We conclude that there are good reasons for using spreadsheets in comparison to traditional GIS software when teaching raster operations. These are demonstration in class, simple user interface, familiarity to students, low cost, flexibility of changing cell values, ease of changing parameters, easy programming environment, and the possibility to look behind the scenes of operations by viewing the code.

Colour Raster Operations

AbstractWe propose a form of three‐input BitBlt/RasterOp which is useful for pictures constructed in a colour‐mapped form as well as in true colour. The model used for this is that of a piece of potentially multicoloured paper on which the picture appears as ink marks. Computationally simple range testing operations can be applied to the source and destination regions to produce many useful effects, some of which we demonstrate. The resulting operations are primitives which can be used to construct more complex operations.

Symbol recognition of equipment location maps with raster operation.

Symbol recognition of equipment location maps with raster operation.