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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116
votes
13answers
48k views

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 (...
109
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5answers
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 ...
72
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7answers
72k views

Finding minimum-area-rectangle for given points?

As you see in the figure, the question is: How to find the minimum-area-rectangle (MAR) fitted on the given points? and a supporting question is: Is there any analytical solution for the ...
62
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2answers
12k views

Acquiring ArcGIS-like speed in Postgis

I have been using Postgis 2.0 for 3/4 of a year now and while I really enjoy using it, excessive query processing time has rendered it basically unusable for my use case. I tend to do heavy ...
46
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3answers
11k views

Are there newer routing algorithms (than Dijkstra, A*) in GIS databases?

There are works like Reach for A* from Microsoft researchers and Highway Hierarchies by Sanders and Schtolz (if I spell the name correctly) from Karlsruhe Uni. Both of them reduce the calculations ...
46
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7answers
110k 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 ...
45
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2answers
11k views

Meaning of Simplify's tolerance parameter

The standard parameters of Douglas-Peucker's simplify algorithm are geometry and tolerance (e.g ST_Simplify in PostGIS). What's the meaning of the tolerance parameter? I know that the bigger the value,...
44
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13answers
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 ...
41
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3answers
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-...
37
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1answer
34k views

Finding center of geometry of object?

Given a set of 2D or 3D points: How to find the center of geometry of an object? According to the following figure, the center of geometry differs from the center of mass if it is calculated in the ...
34
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6answers
46k views

Trilateration using 3 latitude/longitude points, and 3 distances?

I want to find out an unknown target location (latitude and longitude co-ordinates). There are 3 known points (latitude and longitude co-ordinate pairs) and for each point a distance in kilometers to ...
26
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3answers
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 ...
26
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2answers
8k views

Calculating areal distortion outside UTM zone?

One of my colleagues is working with data that is spread across two UTM zone. The majority of the data is in one zone, with a few outliers in another zone. He would like to know what the area ...
24
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2answers
721 views

Seeking Algorithm to detect circling and beginning and end of circle?

I've got lots of flight data from glider pilots in the form of gps fixes in a fixed interval. I would like to analyze the flight path and detect the start and the end of the 'circling' the glider ...
23
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6answers
8k views

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. ...
23
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1answer
952 views

Space filling between random 2D lines

Consider a region (2D) filled with lines randomly (following Figure). We are interested in filling the empty spaces between lines including four boundary edges in a way: 0- maximizing the size of ...
22
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3answers
5k views

Algorithm to find out points of inflection for a polyline

I am trying to find out the points of inflection , i.e. points where the curves in a line start and end. If you look at the image, the green line may be a road or a stream, and the black points are ...
22
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2answers
578 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 ...
21
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3answers
5k views

Finding the Center Line from a set of 3D Points

I have a set of 3D points. They follow a curved pattern with a rather constant diameter as shown below. What would be the algorithm to trace the approximate center line of these points?
21
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3answers
15k views

How to find the maximum-area-rectangle inside a convex polygon?

In this post we are looking for algorithms / ideas on how to find the maximum-area-rectangle inside a convex polygon. In the following figure, numbers are the areas of the fitted rectangles. As shown ...
20
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1answer
4k views

How to Split a Concave Polygon Into Convex Polygons in Arcpy?

I'm looking for a tool or algorithm to detect concave polygons and split them into convex polygons. Like explained in the picture, the blue polygon is split into A and B polygons I'm using Arcpy ...
19
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5answers
4k views

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 ...
19
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5answers
3k views

Algorithm to fix topological errors in GIS software apps

Related question here. I notice that ensuring topological correctness is essential for GIS applications, this is because the input from user or polygon boolean operation can have severe topological ...
19
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2answers
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 ...
19
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1answer
3k views

Robust alternatives to Moran's I

Moran’s I, a measure of spatial autocorrelation, is not a particularly robust statistic (it can be sensitive to skewed distributions of the spatial data attributes). What are some more robust ...
18
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5answers
47k views

Finding if two polygons Intersect in Python?

I'm looking for an algorithm, a high level solution, or even a library which can help me determine if two polygons intersect, in Python. I have the vertices of the two polygons (These are single part ...
18
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6answers
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 ...
18
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3answers
16k views

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 ...
18
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1answer
3k views

Heatmap algorithm to visualise point diversity

Can anyone suggest an algorithm to generate a heatmap for visualising point diversity? An example application would be for mapping areas of high species diversity. For some species, every single plant ...
17
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4answers
4k views

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 ...
17
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1answer
200 views

Alternative indexing methods for point set operations

It is common to use a bounding box spatial index to improve performance when working with a large number of features. Where operations are performed against individual geometries with a large number ...
16
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5answers
5k views

Simplifying polygons to linestring?

I would like to simplify some polygons that represent rivers into linestrings. I assume that holes in polygons can be omitted. Anybody has some good idea how to simply do it? It would be nice, if it ...
16
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3answers
982 views

Clustering undirected lines

I'm looking for an efficient way to cluster lines independent of their direction. That means that a line between New York and Los Angeles should be in the same cluster as a line in the other direction ...
14
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4answers
2k views

Performing dikes extraction from DEM?

I do have DEM of 1x1 meter and original LiDAR point cloud in .las, that DEM is made of. I need to extract river dikes (highest points of the dikes) to vector feature (point, polyline). Any idea for ...
14
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5answers
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 ...
13
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6answers
8k views

Calculating maximum distance within polygon in x-direction (east-west direction) in PostGIS?

I am interested in the maximum width of a polygon e.g. a lake, in east-west direction. Bounding boxes will help only in simple polygons but not in complex concave polygons.
13
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3answers
11k views

Calculating roundness/compactness of polygon?

I am trying to find ways to quantitatively describe the shapes of various polygons. For my project, these polygons represent lakes, rivers, lagoons, and parks. So they can be almost any shape. One ...
13
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10answers
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 ...
13
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2answers
5k views

Is there an optimal algorithm to find the longest shortest path in a network?

I have a large set of linear networks and I would like to find the two ends of each network that are the most distant from each other along the network (on the image below, it would be D to K). The ...
13
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1answer
569 views

Detecting branched polygon shape?

I have a vector layer with millions of polygons making continuous coverage. I need to classify them according to their shape. I am already using several shape indexes from landscape ecology like ...
13
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8answers
751 views

Looking for pedestrian-specific routing engines

Most of the applications providing pedestrian routing I see are sufficient for many needs but not optimal: you cannot cross open spaces like town squares, routing is in the middle of the street etc. ...
13
votes
1answer
270 views

Matching segments of different lengths

I'm trying to match small segments with a larger segment they are the most probably related to: relatively close, similar bearing, and facing each other. Here is a typical example of the data I have: ...
12
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4answers
690 views

How to generalize coastlines?

I have a large set of data points that essentially represent the coastline of the world. I don't know the exact resolution but I'd say it's in the neighbourhood of 5-10m. Imagine a set of points ...
12
votes
4answers
16k views

Bilinear interpolation of point data on a raster in Python?

I have a raster that I'd like to do some point interpolations with. Here is where I'm at: from osgeo import gdal from numpy import array # Read raster source = gdal.Open('my_raster.tif') nx, ny = ...
12
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2answers
3k views

Drawing Day and Night on a Google Map

I'm looking to plot day/night on a Google map, for an arbitrary point in time. I'm familiar with generating map tiles; I'm just looking for an algorithm to tell me whether a particular point on the ...
12
votes
1answer
839 views

Are there any intelligent travelling salesmen?

Jokes aside, I have had a routing problem that is almost a travelling salesman problem (TSP): the starting point is defined the end point coincides with the starting point each node has to be visited ...
11
votes
3answers
4k views

Point in polygon algorithm for multiple polygons

I've a Google map with bunch of polygons on it. Here is a problem I'm interested in: Given a lat,lng point, what's the best way to determine all the polygons that this point lies in? The obvious way ...
11
votes
6answers
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 ...
11
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4answers
918 views

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 ...
11
votes
5answers
14k views

Calculating coordinates of square x miles from center point?

I am trying to create a x mile square (or circle) around a central point, where all sides of the square would be x miles from the centre. I need the 4 corner coordinates. It is scrambling my brain ...