Hot answers tagged theory
As scw points out, you want an implementation of α-shapes. Alpha shapes can be considered a generalisation of the convex hull. They were first described in 1981 in: Edelsbrunner, H.; Kirkpatrick, D.; Seidel, R.; , "On the shape of a set of points in the plane," Information Theory, IEEE Transactions on , vol.29, no.4, pp. 551- 559, Jul 1983 ...
Here is what you are looking for. You can download and test the program: (in java, under GPL license) The paper presenting the algorithm is there: Duckham, M., Kulik, L., Worboys, M.F., Galton, A. (2008) Efficient generation of simple polygons for characterizing the shape of a set of points in the plane. Pattern Recognition v41, 3224-3236
This seems to be a specific application of alpha shapes, which are from my reading a more general form of this problem. R has the alphahull module, which has excellent documentation on computing alpha shapes. Also check this detailed background on alpha shapes. If you only want to compute convex/concave hulls, check out lasboundary, part of lastools, it ...
The Hausdorff distance may be used: matching segments could be 'close' segments according to this distance. It is quite simple to compute on segments. A free java implementation is available in JTS - see here. You may also have a look at the JCS Conflation Suite.
It seems that you are looking for examples of Agent-based Modeling (ABM). There are many GIS models adopt the ABM mechanism. For example, urban planning used lots of cellular automata models that are essentially same as the flocking model. I have implemented a ABM for U.S. logistics industry using AnyLogic to detect the dynamic organizational structure for ...
I created a highly-efficient tool, called [lasboundary][1,2], that computes a concave hull for LIDAR in LAS/LAZ/SHP/ASCII format and stores the result as a vector boundary polygon in ESRI Shapefile format or a geo-referenced KML file. Here is an example run: C:\lastools\bin>lasboundary -i SerpentMound.las -o SerpentMound_boundary.shp reading 3265110 ...
I don't know what would be the "best," because that will depend on the particulars of your segments. A generally good approach is to hash the segments into crucial geometric information. This would include, at a minimum, location of the center (x,y), orientation (0 to 180 degrees), and length. With appropriate weights applied, and some finessing of the ...
Other replies in this thread show that some specialized datums do depend on the earth's magnetic field. However, geodetic datums are determined ultimately by the earth's gravitational field, which establishes the "geoid" (an idealized "sea level," or contour shell of gravitational equipotential). The geoid is then approximated by an ellipsoid of revolution ...
Geographic projections are a way of showing the curved surface of the Earth on a flat surface like a piece of paper... From the Manifold user documentation: Earth is not an exact ellipsoid. In fact, because the Earth is such a "lumpy" ellipsoid no single smooth ellipsoid will provide a perfect reference surface for the entire Earth. The practical ...
James Macgill, Stan Openshaw and I did some more work on cluster detection using flocking boids back in 1999 http://www.geocomputation.org/1999/069/gc_069.htm. This seems to have been followed up by Gianluigi Folino http://staff.icar.cnr.it/folino/papers/ppsn02.pdf. There is also Jameson Conley's work who was a student of James.
The classic (paleogeographer) answer is to use a K-D tree to store the data in (see http://en.wikipedia.org/wiki/Kd-tree). These work by roughly halving the data in to two partitions in each dimension in turn as you move down the tree. The advantage of them is that as you find the nearest item you can also create a list of nearest items as you go for no ...
I've always referred to "Map Projections: A Working Manual", 1987, Snyder, John P. USGS Professional Paper: 1395 which is available as a PDF to download.
JTS (http://tsusiatsoftware.net/jts/main.html) provides a Convex Hull implementation. Martin Davies also mentioned having an Alpha Shape algorithm in the works so you might want to check the SVN repository to see if it is in yet if that's what you want.
Here is an R function that implements the Alpha Hull model. The output is an sp polygon object. Please see the example in the header. It requires the sp, alphahull and maptools packages. ###################################################################################### # PROGRAM: ConvexHull # USE: CREATE CONVEX HULL USING THE Pateiro-Lopez ALPHAHULL ...
I've written code to handle sloppy line segment matching (and overlap them) in Boundary Generator. I wrote up the (fairly elementary) math behind it here: http://blog.shoutis.org/2008/10/inside-boundary-generator-computational.html. The code is open source & linked from that blog post. The code follows a really simple approach: A segment-segment test ...
Here comes an idea If you tear apart one of the linestrings to compare and test if the vertexpoints is within some distance from the other linestring to compare you can control the test in many ways. those examples work in PostGIS (who could guess :-) ) First, if we say that there is a match if all vertex points in a linestring in table_1 is 0.5 meters ...
I worked on a project with a similar requirement about 5 years ago. It involved combining coordinates from street centerlines (with relatively high coordinate precision) with Highway Performance Monitoring System (HPMS) traffic network links. At the time the FHWA didn't provide any tools to do this sort of thing. That may have changed, you might want to ...
Good accounts of algorithms in 2 and 3 dimensions appear in the classic text by Preparata & Shamos. Algorithms used in GIS are a specialty of Hanan Samet, who has published several books on the subject. Higher-dimensional searches are usually assisted or sped up by means of preliminary data mining, clustering, or dimension-reducing techniques. This is ...
In general, implementations of ABM are written in agent-based environments, most of which aren't full fledged GIS systems but may be able to use GIS data. One of the challenges of incorporating these kinds of models into a GIS is their strong temporal aspect: each agent is changing over time in response to surrounding agents. Because a typical GIS focuses on ...
In this case the forth dimension is measure as gissolved mentions, but more commonly the fourth dimension does refer to time. Historically, most GIS systems have been weak at integrating time, but the increase in dynamic modeling over the years has brought time into most current GIS systems. See for example this recent question. While the software has been ...
More detailed and with all the information you need, the Coordinate Conversions and Transformations including Formulas document gives you a detailed explanation of the map projections and the formulas necessary for executing coordinate conversions and transformations (suported by the EPSG dataset).
I liked Datums and Map Projections: For Remote Sensing, GIS and Surveying from Jonathan IIiffe and Roger Lott. Make sure you grab the second edition. However, it still has some errors. Nevertheless you get some examples to practice.
There are also geomagnetic datums (data?) out there which of course are affected by the movement of the magnetic poles. There was a related question about it just yesterday and it provides a concrete example: How can I convert geomagnetic coordinates to geographic coordinates without doing the math myself?
I've heard that Netezza has implemented some innovative spatial parallel processing algorithms. The whitepaper is here. Netezza’s Asymmetric Massively Parallel Processing architecture provides the best combination of symmetric multiprocessing (SMP) and massively parallel processing (MPP), facilitating terascale, complex query processing of ...
What is meant by By using this property, stops within one route analysis layer can be assigned to multiple routes. is that you can specify to which route your stops will be assigned. So, say you have two cars and multiple delivery stops. By specifying a route name, you specify what car (route) will serve this point. So the phrase above say you are ...
QGIS can generate histograms and basic statistics about the image. GRASS gis can also generate statistics (r.report) and manipulate each band or compositions with a wide range of function (http://grass.fbk.eu/grass64/manuals/html64_user/raster.html). They both open source but Qgis is a little bit easyer to get started, just open a new project and add a ...
There is a new Addon for GRASS GIS 7 available: v.concave.hull. See also http://grasswiki.osgeo.org/wiki/Create_concave_hull
Here's a program written in C that computes convex hulls, alpha shapes, Delauney triangluations and Voronoi volumes: Hull - Ken Clarkson (2002) Another convex hull algorithm with C and Java implementations is here: Convex Hull (2D) - Computational Geometry in C, Joseph O'Rourke (1998)
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