# Questions tagged [algorithm]

A mathematical procedure used to solve problems with a series of steps. Algorithms are usually encoded as a sequence of computer commands.

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### Is there any pseudocode for MFD (multiple flow direction) algorithm available?

Still stuck with the simulation system, is there any good pseudocode for the multiple flow direction (MFD) algorithm? I read a pseudocode example and implemented it, however the simulation was linear: ...
841 views

### Best routing algorithm for this scenario

Trying to work out the most appropriate routing algorithm to use for this situation. Even better if it's available as part of pgrouting or similar.. Here's the requirements: Specified date/time for ...
434 views

### How can Flocking Algorithms be used in GIS?

The first flocking algorithm was written by Craig Reynolds in 1986. A recent browser implementation can be found here.              &...
585 views

### How does Watson solve Geography problems?

In spite of losing to humans on the geography question, Watson still won Jeopardy. The explanations regarding this incorrect answer seem a bit lame to me (at 3:40 in the video). With a logo like ...
459 views

### Auto Balancing in EarthWork

I am not sure whether this question belongs here. I think it belongs more to Geo-technical, but anyway, I just give it a shot. During earthwork development, earth terrain has to be cut ( if the ...
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### Algorithm to calculate coverage + overlaps from a set of arcs

I have a shapefile containing arcs representing the path travelled by a truck spreading fertiliser onto a farm. Let's say I know the spread width is 30m, i.e. the truck can spread fertiliser 15m ...
4k views

### Algorithm to find polygons enclosing points

I'm trying to find an algorithm that can determine the smallest possible polygons to cover a number of points. I know how to get the convex hull around all the points, but say that the points are ...
17k views

### Clustering trajectories (GPS data of (x,y) points) and mining the data

I've got 2 questions on analyzing a GPS dataset. 1) Extracting trajectories I have a huge database of recorded GPS coordinates of the form (latitude, longitude, date-time). According to date-time ...
111k views

### Calculating Latitude/Longitude X miles from point?

I am wanting to find a latitude and longitude point given a bearing, a distance, and a starting latitude and longitude. This appears to be the opposite of this question (Distance between lat/long ...
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### PostGIS: split a polygon in a given ratio

Is there a convenient way to split a polygon into n parts, more-or-less equal in size in PostGIS?
25k views

### Map matching links and ideas? [closed]

I'm using OpenStreetMap and its vectorial road network and I'd like to implement a map matcher algorithm. Currently I'm able, for each GPS position, to retrieve the nearest road segment and ...
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### Algorithms for matching segments

What are the best algorithms to match segments? I'm trying to match corresponding segments from two map sources, one less accurate but with segment names, and one more accurate without segment names. ...
743 views

### How to split polygons without ArcView? [closed]

I'm trying to split polygons into equal areas. While fishnet sort of works; the areas I'm trying to split don't touch; they're national parks. Fishnet spans the whole area, not just the polygons in ...
28k views

### Finding boundary co-ordinates from given set of point co-ordinates?

Given a set of coordinates, How do we find the boundary coordinates. <== Figure 1 Given the coordinates in the above set, How can I get the coordinates on the red boundary. Boundary is the polygon ...
3k views

### Incremental spatial clustering algorithm

I'm in search of a incremental spatial clustering algorithm. Here is my use case: users create entries with an initial position users may change the positions of existing entries I now want to ...
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### Create centreline from a polygon [duplicate]

I am working on a project to create a centerline from a polygon automatically. The user select a polygon and click a button, the centerline will create for him. I have tried the build-in function “...
10k views

### Dividing polygon into specific sizes using ArcGIS Desktop?

I have several thousand irregularly shaped polygons in a shapefile. I want to be able to split each polygon into three areas, and to specify what the size of those areas (they sum to the previous ...
7k views

### Lines to Polygons

I have failed to find the "name" of the algorithm that would allow one to convert lines to polygons. Since this issues crosses GIS and the fields of computational geometry and computer science. I am ...
38k views

### Why is law of cosines more preferable than haversine when calculating distance between two latitude-longitude points?

In fact, when Sinnott published the haversine formula, computational precision was limited. Nowadays, JavaScript (and most modern computers & languages) use IEEE 754 64-bit floating-...
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### Algorithm to find nearest point

I've a list of a few hundred cities with their latitude/longitude. Given another location (also in lat/long) I need to find the nearest city. As I don't use any GIS, by now the obvious algorithm is ...
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### Seeking algorithm to place maximum number of points within constrained area at minimum spacing?

I have a polygon layer that describes a constraint; I wish to add points within this area. I want to add as many points as possible, but they must have a minimum spacing between them. Is it possible ...
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### Good resources on geocoding algorithms

Do you know of any good resources on geocoding algorithms? I am particularly interested in address query parsing, including matching and weighting parts of the query, dealing with misspellings and ...
2k views

### Find the best path along raster

I've just posted a question to StackOverflow about the best way to go about finding the best path on the raster below (where whiter pixels are 'better'), but have realised that it might actually be ...
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### Retrieve polygon smallest MBR

I have a postgis table containing polygons. I want to transform my polygons to 4 points polygons : retrieve the smallest MBR. Here comes an illustration of what I want : My original polygon is in ...
1k views

### Transform SPOT5 images to natural color images

We're currently using PixelSense to convert raw SPOT5 images to natural color ones for display and printing. Do you know a good algorithm to perform the same task as we want to ingest raw images in an ...
770 views

### How to calculate buildings shadow areas

Is it possible to calculate shadow areas of buildings or simulate shadows of buildings in a city using e-cognition software, with the DSM of the buildings and the sun angle and azimuth known?....If ...
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### shadow simulation from buildings [duplicate]

is it possible to use hillshade function in ArcMap to calculate shadow areas of buildings or simulate shadows of buildings, using DSM of the buildings and the sun angle and azimuth?
183k views

### Algorithm for offsetting a latitude/longitude by some amount of meters

I'm looking for an algorithm which when given a latitude and longitude pair and a vector translation in meters in Cartesian coordinates (x,y) would give me a new coordinate. Sort of like a reverse ...
8k views

### Finding tunnel center line?

I have some map files consisting of 'polylines' (each line is just a list of vertices) representing tunnels, and I want to try and find the tunnel 'center line' (shown, roughly, in red below). I've ...
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### How can a single line be computed from multiple possibilities

I have datasets containing continuous GPS streams of data that represent routes or trails. For any given route, I probably have at least 5 (in some cases many more) different sets of data. Given that ...
13k views

### Algorithm for finding irrregular polygon centroid (label point)

I need to find a centroid (or label point) for irregularly shaped polygons in Google Maps. I'm showing InfoWindows for parcels and need a place to anchor the the InfoWindow that is guaranteed to be on ...
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### Parameters for ED50 -> ETRS89/WGS84 seven-parameter transformation which are good for Denmark?

I am looking for parameters for a seven-parameter transformation (Rx, Ry, Rz, Tx, Ty, Tz, s) from ED50 UTM (zone 32U) to ETRS89 and/or WGS84. The best match I could find is here: http://geodesy....
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### Tools for importing historical maps into modern GIS systems?

What tools exist to derive geometries for use with modern GIS systems from older scanned maps? I am referring more to libraries that generate actual data rather than present an interface for ...
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### How do I calculate curvature using GIS co-ordinates [closed]

I have GIS data for which I would like to calculate where curvature is present. Anyone has done this before, please help.
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### What are Definition, Algorithms and Practical Solutions for Concave Hull? [closed]

Convex Hull A convex hull of a shape is defined as: In mathematics, the convex hull or convex envelope for a set of points X in a real vector space V is the minimal convex set containing X (...
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### Point Pattern Analysis Algorithms

I'm looking for point pattern analysis algorithms and literature on point pattern analysis, online resources and book titles welcome. The topics may range from general descriptions of algorithms to ...