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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2
votes
0answers
102 views

Find and destroy duplicate OSM multipolygon/polygons in TileMill/PostGIS

In OpenStreetMap there are sometimes multipolygons where attributes are present on both the polygon and the multipolygon relation, such as the Grampians National Park: ...
2
votes
1answer
149 views

How to discretise a line into grid lines

Having a line and a grid, the aim is to discretise the line into grid lines. In the following figure, the given line is in black, its intersections with grid lines are blue, the desired is set of ...
0
votes
0answers
73 views

Route through water polygons

I have a water-polygon grid shape file as shown (Each grid is 1latx1long): I have created this in QGIS and files (coastal lines and land polygons) selected from http://openstreetmapdata.com/data ...
3
votes
2answers
132 views

Breaking a range of values into buckets for a gradient

If I have a range of values and want to make a choropleth map with a gradient, what algorithms are out there to determine the value ranges for the different colors in the gradient? For example, if I ...
0
votes
2answers
438 views

Detecting invalid polygons (self-intersecting or touching)

An invalid polygon can be defined as one that intersects itself, or one where the lines make contact, ie, the two shapes at the top of this picture. Given the XYPoints of a polygon, what logic ...
3
votes
1answer
263 views

How is slope of a surface in an arbitrary direction produced?

I am currently developing a program that requires that I calculate the slope for each cell in a DEM. However when I try to understand the algorithm to be used I get stuck trying to understand exactly ...
8
votes
2answers
257 views

Creating an “average” polygon

I found this thread in the old ESRI forums with the same type of problem I am facing today. The solution to the problem is explained in little detail and since I am not an expert, I was wondering if ...
4
votes
2answers
252 views

What is the algorithm used by ESRI for finding loops in a geometric network?

I've been trying to develop some code for ArcMap (VB .net) that would take a river network, identify and label the loops. These loops can be simple bifurcations or highly thread braided channels. I ...
0
votes
1answer
1k views

NED (LTP) to ECEF Orientation Conversion (Tait Bryan Angles)

I have an application where I need to convert an orientation from NED - given a WGS84 latitude and longitude - to ECEF. I have yaw, pitch and roll as Tait Bryan angles (XYZ) relative to the local ...
3
votes
5answers
419 views

How can I count overlapping polygons, resulting in a new set of polygons?

I have 100 polygons in a GeoJSON file that partially overlap each other. I would like to produce 100 new polygons as follows: The area covered by any of the original 100. This is their union. The ...
1
vote
2answers
111 views

Frequency of partially or fully overlapping lines

Let L be a set of line-segments (lines) in a two-dimensional (2D) Euclidean space that are randomly (say, using uniform random function) distributed, that is, some may overlap other(s). Overlapping ...
2
votes
1answer
144 views

Center point approximation of a polygon

I would like to get a center point approximation of a set of polygons so I can do a NN lookup to use for assignment instead of a point in polygon query. Lets say I have this set of polygons: I ...
4
votes
1answer
121 views

Which spatial bundling or grouping algorithm optimally groups elements by attribute?

As I delve deeper into GIS, I find myself trying to improve efficiencies of certain procedures and processes. The one process I'm working on now is spatially scheduling construction projects. For ...
2
votes
0answers
153 views

Iteration based positioning on Matlab - retrieving coordinates between iterations

This is my first question on SE so let me know if I'm not asking my question in the right place. So basically, I have an algorithm which uses UMTS measurement events for positioning estimation, which ...
3
votes
1answer
99 views

Placename matching algorithms and services for geocoding

Are there any placename-specific matching algorithms, routines or services available? By placename specific I mean not just a simple string-difference match, or soundex/metaphone, but something that ...
-1
votes
1answer
84 views

How to find the most east or west longitude around the date line

I've got a python script that is comparing extents of rasters in various projections. Generally it works, but sometimes, especially when the rasters are global in extent or cross the dateline it ...
1
vote
0answers
164 views

Divide polygon evenly based on lines and intersection points

I have this purple polygon illustrated in the figure below. I would like to split the polygon so that each line segment (green) split the polygon evenly with the surrounding line segments. A line ...
4
votes
1answer
256 views

meeting point minimizing travel distance for participants?

The problem is to find the point minimizing the travel distance for around 100 persons in different regions who want to meet in the same place. Travel is by car not by plane. Assuming that I get ...
0
votes
1answer
296 views

How do I choose parameters for the Huff model that best fit my data?

I'm using the Huff model for some analysis I'm doing. For those not aware, the Huff model is a probabilistic model for retail trade area analysis. H_ij is the probability that a person at location ...
1
vote
0answers
88 views

Kalmanfilter GNSS IMU

I want to make an uncoupled Kalman filter. The input data are GPS and the output of my strapdown Algorithm from the IMU. The Strapdown Algorithm is used to calculate the actual position and velocity ...
6
votes
1answer
120 views

Open source implementation of “feature density” algorithm

I'm working on a dataset of house searches - 1 polygon for each area in which people want to find a house from an online search tool. This produces many overlapping polygons. It would be great to ...
1
vote
2answers
554 views

How to convert self intersecting polygon to multipolygon?

Working with the union and polygonize methods in GDAL/OGR, I often end up with self intersecting polygons. The case is one polygon which essentially consists of two polygons: In the above example, ...
1
vote
1answer
100 views

Algorithm to find the polygon ID where a point belongs to

I am wondering what is the simplest way to perform a look up of polygon Id based on the point location. Input: a point with coordinates, a table of polygons Output: the polygon Id where a point is ...
1
vote
0answers
46 views

Indexing GIS data associated with user with timestamp

I have data for each user in this format user1:(timestamp,lattitude,longitude) user1:(timestamp1,lattitude1,longitude1)..... Here the 1 at the end of timestamp/lat/long is to specify a different ...
0
votes
1answer
30 views

How to contribute for pgrouting.org [closed]

I wanna to contribute for algorithms, that's why i chose pgrouting can anyone help me out and suggest me more organisations to which i can contribute. Thnks.
1
vote
0answers
116 views

Algorithm to match trajectory [closed]

I've data in the format (lattitude,longitude,timestamp). What I want to do is between timestamp1 and timestamp2 I want to find out which people might have taken the same routes. Is there some kind of ...
1
vote
1answer
205 views

How does QGIS calculate the area of a polygon?

I am working on a project that requires the calculation of the area of a polygon by two different methods. I need to know what algorithm QGIS uses to calculate the area of a polygon. I know ESRI ...
2
votes
3answers
663 views

Efficient algorithms to split and join lines?

Referring to the Figure below: How to efficiently join segments into lines? How to efficiently break lines into segments? The above will be applied million times.
1
vote
0answers
82 views

An algorithm for locating candidate labelling boxes within a polygon

Has anyone implemented this algorithm In PostGIS? Quoting from the paper: Vector-based geographic information systems usually require annotation, such as a polygon number or attribute data, in a ...
5
votes
2answers
402 views

inner convex-hulls in a set of 2D points

A set of 2D Points are scattered randomly (i.e., no specified pattern), we are interested in finding all inner-convex-hulls (ICH) in an order of largest in area to a minimum until the entire study ...
4
votes
0answers
195 views

GPS data based track/trip calculation algorithm available?

Currently I'm receiving position data of moving assets every 90 or 120 seconds (depending on the asset). What I'd like to achieve now is to detect standstill and movement phases (tracks/trips) on the ...
0
votes
2answers
345 views

How to split a linestring every 1000 points in postgis

To assume compatibility with my survey software, I would like to lighten geometries of my linestrings by cutting them every 1000 points without creating or interpolating points. I transformed a ...
14
votes
3answers
1k 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 ...
7
votes
2answers
169 views

Generating polygonal blocks using growing lines

We first generate a set of locations (i.e., points(x,y)), randomly. Then we assign for each point a number showing the angle of a line being centred at that point. The criteria for the length of lines ...
6
votes
4answers
358 views

Generate polygons from a set of intersecting lines

This is a simple and quite common question which has already been asked for different purposes (see this link and this too, for example), here, however, we are looking for not a software package but ...
4
votes
1answer
310 views

Which flow routing algorithms does ArcGis support?

Other than standard D8 are there support for multiple flow algorithms like FD8, DEMON, Dinfinity etc?
3
votes
1answer
312 views

Find projection of a point to a line

I have a segment defined by 2 LatLon points(A and B) and a third LatLon point (C). I need an alghorithm, formulae, or some code to find the projection point of C on the segment AB (call this point D) ...
3
votes
0answers
39 views

Clustering driven by an enum/list

Given a set of 2D points ( or vertices if you want ), the values stored for each point are: coordinate on x coordinate on y an enum or a value from a list in general for the sake of this example ...
0
votes
1answer
115 views

Algorithm to merge adjacent raster datasets

I am trying to figure out how to merge adjacent raster datasets. Is there any clear algorithms (may be a pseudo code)?
15
votes
1answer
675 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 ...
0
votes
1answer
848 views

How do services like Google Maps compute the set of instructions for a route?

The problem of computing the driving directions from A to B can be divided into two equally important parts: Finding the best path from A to B. Identifying all the relevant maneuvers along that ...
7
votes
2answers
187 views

Hashing functions for GIS data

I would like to take geometries from a vector dataset and reduce them to a hash. This hash would then be used to verify the integrity of that data and also identify identical geometries. Do any ...
4
votes
1answer
322 views

Splitting large polygons

We need to split large complex polygons into smaller chunks ( Where the area <= x). The tricky bit is that they can only be split where the distance from one side of the polygon to the other is ...
3
votes
1answer
159 views

Curve from a Douglas-Peucker line

When generating a line using the Douglas-Peucker Algorithm the resulting object is a line with steep angles, I would like to "smooth" that line and making it look less "squarish" using curves, like ...
10
votes
2answers
317 views

Algorithm: move a source polyline to a reference polyline (completely or maybe partially)

In our system, there're the requirements that we want to move some source lines (with low precision) to reference lines (with high precision). Following pictures gives the normal use cases. The red ...
3
votes
1answer
109 views

Learning resources for beginning differential topology for a programmer? [closed]

With this question I'm looking for suggestions about how and where to start learning differential topology starting from a good base of linear algebra and geometry, also consider that this know-how is ...
12
votes
8answers
326 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. ...
4
votes
1answer
245 views

Simplification algorithms for 3D topology

My problem is about simplifying a given topology that can be opened ( an usual 3D reconstruction of a given square on a map ), totally closed (like a perfect sphere) or a topology with holes ( a ...
2
votes
0answers
126 views

oil palm stand census algorithm

Anyone have experience in oil palm stand census using tree detection algorithm from satellite images in ArcGIS or QGIS? any references for usable algorithm? What is the accuracy? thanks for help.
2
votes
1answer
273 views

Intersection of convex polygons on a spherical surface

There are a number of algorithms available for the intersection of two convex polygons, but I am interested in an algorithm to find the intersection of two convex polygons on the surface of a sphere, ...