# Tagged Questions

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

138 views

### Longest common prefix of geohashed points

I currently use Geohash to index some points and retrieve information faster by providing a geohash prefix for a given point for a given distance.. For example if I get a given point at '1600 ...
56 views

### What are problems & biases stemming from mathematics behind using Monte Carlo Markov Chain to make heatmap?

My buddy and I are using Monte Carlo Markov Chains to make a heat map - in the interest of rigour, and out of curiosity: "What are the problems & biases that stem from the mathematics behind ...
2k views

### Splitting Linestrings on the dateline with OpenLayers

A couple of years ago I posted a questions titled "The International Date Line wrap around" @jdeolive suggested I split the features at the dateLine. So I tried. So when I try to split my satellite ...
75 views

### What graph traversal algorithm should I use?

I would like to write an algorithm which can traverse a graph and hopefully later I can implement it to use for an indoor navigation system. The graph would come from floor plans of a building and the ...
310 views

### Delete duplicate spatial point/points in mssql from a perticular location

I am working with a Spatial data which has a street intersection points.... I get the intersection points from spatial query on street/roads datain MMSQL . but in my case some streets/roads are multi ...
51 views

### how to assign unique attribute value per neighborhood? [duplicate]

I have a feature class of adjacent polygons and I want to assign an integer attribute value to my polygons based on the following rules : a polygon must not have the same attribute value than any of ...
439 views

### Is there a method in SQL Server (2008 or 2012) that will return the equivalent of the Esri LabelPoint for geometry?

I'm looking for a method that is equivalent to the Esri LabelPoint for SQL Server Geometry (or fairly close). Does it exist by a different name? Or is there an after-market implementation? I found ...
138 views

### Line defined by two geographical points crossing circle area with defined radius

I'm trying to calculate the amount of lines defined by two geographical points crossing a circle area defined by a center and radius. I've tried to use algorithm discussed here, but in my case it ...
291 views

### How can I always run an algorithm with standard input shapefiles from mapcanvas in QGIS 2.0.1?

I created a model in the graphical modeler and I want to run that model always with two specific polygon shapefiles from my project, e.g. pst and astenot. Whenever I run my model, it asks me to set ...
104 views

### When was MFD renamed to FD8?

According to my understanding, the Multiple Flow Direction (MFD) algorithm was originally defined in The Prediction of Hillslope Flow Paths for Distributed Hydrological Modelling using Digital Terrain ...
86 views

### Divide a Square to a serval equal squares using Acrgis [closed]

hi i'm looking for an algorithm to split a square to a SEVERAL equal squares: i have only : x min , y min x max , y max please see picture (not valid picture only to describe problem): any ...
1k views

### Spatial databases in location based search

I'm developing a location based application in which i was in the plan of dividing the globe into grids and when the client requests information, will create a table or similar data model which will ...
826 views

### Lossless Polygon Simplification?

Is there a standard/recommended algorithm for simplifying a polygon without shrinking any of its original boundaries? Right now I'm using TopologyPreservingSimplifer within JTS and running into ...
91 views

### Exploratory search for clusters in point data

This is a more conceptual than practical question and is about exploratory cluster identification. While there are very specific meanings in the geography canon as to what they are, in economics they ...
3k views

### How can I Destripe Landsat Images?

I am working with Landsat 7 ETM+ SRC-off imagery. I'm doing some land-cover classification for a place in Kenya. My problem is the no-data stripes in the image. Is there a way in which I can ...
115 views

### Good algorithm to detect “wrong” features in a vectorial coverage

I am working with a bunch of shapefiles. Each shapefile consisting in rectangles with an integer attribute representing the strength of a signal. I serve these vector files as overlays on a base map, ...
454 views

### How to number polygons according to their spatial relationships?

I have, for example, this layer in postgresql (polygons): table : poly (objectid: integer, num: integer, shape: geometry) I want to enumerate the polygons from left to right and top to bottom ...
289 views

### Fast Clustering Algorithm for Geographic Data?

I have been browsing through the net in my attempt to find a fast clustering algorithm to cluster geographic points, but lot many of the results found were for clustering algorithm in general and not ...
2k views

### Similarity between two raster maps

Having two raster maps as the examples below: We are interested in evaluating their similarities. As shown, they are not fully overlapping. We guess one way is to clip small one area from the ...
195 views

### Finding a route with desired cost not minimum cost

The goal of routing is usually finding the route with minimum cost. That cost can be distance, time, calories or some other value but still our desire is to find the route that costs least. But what ...
217 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: http://www.openstreetmap.org/...
312 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 ...
324 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 ...
522 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 ...
1k 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 (...
1k 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 ...
471 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 ...
477 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 ...
4k 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 ...
976 views

### Counting overlapping polygons in GeoJSON to result in 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 ...
228 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 ...
310 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 ...
216 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 ...
275 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 ...
179 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 ...
240 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 fails....
286 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 ...
687 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 ...
1k 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 ...
149 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 ...
215 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 ...
2k 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, ...
150 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 ...
73 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 ...
32 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.
420 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 ...
438 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 ...
2k 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.