# 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.

488 questions
Filter by
Sorted by
Tagged with
6k views

### Fix Self Intersecting Polygons Manually [closed]

I are looking to implement a method to fix self-intersecting polygons by editing the vertex order. We want to take the polygon rings and re-arrange/add in vertices to make a valid polygon. This is ...
1k views

### How do I convert a screen position to geographic coordinates?

I'm looking for resources that explain how I should convert screen coordinates (the point that I pick on-screen) to geographic coordinates (lat / lon). I want to build an application where, the ...
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?
70 views

### Geoserver labeling algorithm

I'm really interested in knowing what kind of algorithm does GeoServer use when presenting its maps. GeoServer has its own algorithms, for instant the labelling algorithm. Is there a possibility to ...
1k views

### How to calculate a set of minimum bounding boxes for a polygon

I need to calculate a set of minimum bounding boxes for a polygon. Id est having a complex polygon I want to envelope it with a set of small boxes instead of a big one.
101 views

### Calculate an intersection point of multiple spheres on the surface of earth [duplicate]

The question i am going to ask is very much similar to this question-How to calculate the intersection of 2 Circles? But the problem here is, the radius of the spheres are too small (within 8 meter). ...
56 views

### Assign points with varying radii to central meeting locations

I have a set of points in a city, each with a maximum distance radius of 0.5 - 1.5 miles. From this set of points, I'd like to create a small number of 'meeting points', i.e. locations that are ...
665 views

### Segment matching on a polyline

I have about 1000+ running routes which I can load into memory as polylines using latitude and longitude data captured from a running watch. From these polylines I would like to be able to identify ...
1k views

### Calculating a point Lat/Lon from another Lat/Lon point angle

I need to make an algorithm: : I have a point O center of a circle of radius r, on this circle there is two point P1 and P2. I know latitude and longitude of point O in degrees I know the radius r ...
509 views

### ArcGIS - Flow Direction (Algorithm) [closed]

I am curious about the algorithm of Flow Direction in ArcGIS. Recently I am studying about Hidrology, and I have some questions regard to Flow Direction in GIS. The size of this cell is 100m x 100m, ...
767 views

### How to programmatically partition a large Polygon in smaller parts within a given Area Threshold?

I'm looking for a Java library, or even an algorithm to do the following: I have a large polygon, about the size of a large city. I need to break it down into smaller polygons such that: The area of ...
2k views

### How to calculate the Oriented Bounding Box (OBB) of a polygon or point set?

I'd like to calculate the "Oriented Bounding Box" (OBB) which is the enclosing rectangle aligned to the longest extent of a point set (which is not necessarily aligned with the axes of the co-ordinate ...
259 views

### Is Hershbergers improved Ramer-Douglas-Peucker algorithim worth implementing?

Here is the article with code samples Other than the C code he wrote are their any implementations? Is it worth making a python or R module out of the C code? Are their known flaws to the algorithm? ...
162 views

### Geoserver (automatic labeling generalization) [closed]

I am a Master student looking to do my thesis in cartographic labelling using GeoServer. The thesis topic will be something like "Cartographic Labelling in Real Time Mapping using Web Services. I am ...
81 views

### Determine when heading off course

How does google or other map providers with routing capabilities determine when you are not staying at the right course? I am trying to figure out how to implement this feature in my gps that I am ...
93 views

### Algorithm to scan a road network geometry using directions service

Let's suppose there's a Directions Service which, given a pair of points, returns the geometry, along the network, which best connects those points (which are previously projected - "snapped" - to the ...
644 views

### Covering polygon with fixed size squares?

Can you please advice me of an algorithm (which I can implement in a Java) to cover some polygon (not exact cover) with squares of certain size (aXa squares)? The cover doesn't have to be exact - ...
1k views

### How to find if two gps tracks were from the same trip?

Given I have gps tracks from many users running or hiking, how can I find out who were running together? In other words, which algorithms are there to find out who were in the same party? Haven't ...
253 views

### Is this Intersect or Union algorithm associative?

Similar to Is the Intersection Operation Commutative? . Spoiler for that one: Intersection is commutative and associative. I've created an algorithm (in PostGIS but the theory would work in other ...
1k views

### Best flow routing algorithm for determining location where spill enters stream?

What would be the best flow routing algorithm for determining the quickest (and by this I suppose I mean shortest) path that a spill would take when traveling to a stream? My best educated guess ...
955 views

### library for minimum bounding box “by width” in javascript or python

I'm looking for a library (or at least a code snippet) to calculate the minimum bounding box "by width" in javascript or python. Below is an illustration from the ArcGIS documentation of that ...
170 views

### A Distributed Cost-Distance Algorithm

I'm currently trying to implement a distributed cost-distance algorithm, however I can't seem to invent my own and still make it fast. I've been googling around a bit but haven't found anything that ...
412 views

### Using netCDF4 Python climate algorithm?

I have been working in Python with the Acaconda Python distribution to create code that accomplishes the following algorithm: I have multiple variable netCDF4 files [NCEP Reanalysis tmax(K), tmin(K), ...
36 views

### Getting incorrect results for Geary's Coefficient algorithm (incorrect math?)

I'm not sure if anyone here can help me with this, but I'm currently working on a program that uses a spatial autocorrelation algorithm to analyze patterns in an image. It's supposed to return values ...
544 views

### J2000 to WGS84 in QGIS?

How to transform Earth-Centered Inertial J2000 CRS to WGS84 CRS in QGIS? I searched J2000 in spatialreference.org, however nothing found. I don't know the proj4 string of J2000. Any advice would be ...
1k views

### Is there an algorithm for transforming from CGCS2000 to WGS84?

Is there an algorithm that supports transforming from CGCS2000 coordinate to WGS84 coordinate? CGCS2000 is China Geodetic Coordinate System 2000. Any advice would be thankful!
261 views

### How to assess quality of the TSP algorithm?

I'm trying to develop my own algorithm for solving Travelling Salesman Problem (TSP) I tested it (in its current state) on the "att48" instance of the TSPLIB and got following results: As we can see ...
163 views

### Aggregating river basins

I am not a hydrologist but am providing GIS infrastructure to our hydrology department which actually doesn't use GIS very much yet. Therefore I am asking for some hydrology related insights. Btw: We ...
718 views

### Which algorithm does gdal_polygonize use?

I would like to know which algorithm (i.e. Sobel operator ) is used to extract the polygons in gdal_polygonizer. I searched here and here but could not find it.
93 views

### Algorithm to find the boundary grid points [duplicate]

Let us consider a set S consisting of a collection of grid locations (i,j),i,j=1,\ldots,n, in 2-dimensional gridded plane. Here the point (i,j) corresponds to a rectangular grid in the X-Y plane. ...
185 views

### using MCA in GIS for suitability analysis [closed]

I have an essay about using MCD methods to solve suitability analysis. I must write a scenario about fuzzy membership, WLC and AHP. I feel that I’m confused about when and where to use each method. ...
1k views

### Free implementation of Polynomial Approximation with Exponential Kernel (PAEK) algorithm

I need a Free (i.e. Open Source) implementation of the Polynomial Approximation with Exponential Kernel (PAEK) algorithm, preferably in C, C++, Python, Julia or R. The algorithm is one of the ...
126 views

### Finding boundary vertices from given set of coordinates? [duplicate]

How to find the the boundary co-ordinates from a given set of co-ordiantes? I understand that this question asked previously and answered here Finding boundary co-ordinates from given set of point ...
1k views

### Fast raster combine using rasterio

I'm trying to duplicate the functionality of ArcGIS's Combine function within rasterio. Given a list of (presumably categorical) rasters read with rasterio, I want to output a combined raster and a ...
628 views

### How do the equations/algorithms behind buffering tools actually work?

I've been wondering how the equations/algorithms behind buffering tools actually work?
2k views

### Buffer Zone Algorithm

I use google maps, php, mysql, and I want to create a buffer zone in line among some points. Could someone tell me where can i find the algorithm (php library or the math in order to implement it) to ...
23k views

### How to calculate grid convergence (True North to Grid North)?

I would like to know how to calculate the grid convergence angle between True North and Grid North for UTM maps. I am using ArcGIS 10.0 (ArcView licence) and have used the Calculate Grid ...
46 views

### Buffering/extrusion of a dem surface

I have a surface representing a DEM and i would like to add it some thickness. If i simply duplicate the surface and translate it down by my thickness, i get non uniform thickness, ie thinner where ...
280 views

### Find a path between an origin and destination given scattered points

We have a postgis database containing a lot of ordered (by date/time) nautical point (lat/long). Each of these points are affected to a leg between an origin and a destination (both origin and ...
136 views

### Locating Moon in Sky from Earth

I am working on project which need to find moon location from a specified lat, long on earth. So basically info I am having is Lat,Long and Timezone. Format of the moon location Info? So first in ...
855 views

### Interpolate data from multiple gpx tracks

I have a number of GPX tracks of the same road. But due to GPS error they are not accurate enough (20-30m off). I'm wondering if I could interpolate those multiple gpx tracks into single one. If an ...
268 views

### Calculating the fastest routes and some points on the same time

I have two drivers and each driver has a set of about 15 locations where they need to drive to on a single day. Calculating the shortest route for both drivers is not the problem (using a matrix ...
45 views

### How do I map points on a 2D map to a 3D illustration of the same area? [duplicate]

I'm looking for advice on how to build an algorithm that maps any point on a map to a point on another map, interpolating where needed. Let me better clarify with an example of what I concretely need....
691 views

### What are definitions of watershed segmentation, local maxima, variable window search, regarding LiDAR for vegetation?

I am not familiar about Lidar. I want to measure trees height and number of trees. I guess, watershed = to locate the trees, local maxima = to measure trees height. I used these methods in SAGA GIS. ...
2k views

### D8 algorithm to get the flow direction in ArcGIS

I am using ArcGIS 10 for the get the flow direction from DEM. I wonder about the algorithm they have used while calculating flow direction. It is mentioned there that it is using D8 model. D8 model ...
703 views

### What is an efficient Algorithm to draw a straight line from points?

I have some cross section survey data, which is like this: X Y Z pt_dt 2970969.635 359725.0088 83.4242 1-x 2970968.278 359722.2182 83.2591 1-x 2970941.771 359670.127 83.0655 1-x 2970961.369 359708....
323 views

### Buffering algorithm [closed]

Does anyone know the algorithm of buffering? I had difficulty in drawing buffers. So I tried many values to acquire 1km buffer. I found value 0.008966 produces 1km buffer. Then I calculated inverse ...
261 views

### Is it possible to create a standalone model in ArcMap Modelbuilder?

Is it possible to create an algorithm in ArcMap Modelbuilder that could then become a fully standalone applet? I would like to be able to provide this processing algorithm even to users who do not own ...