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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4
votes
2answers
8k views

Calculate bearing between two decimal GPS coordinates

I'm building a virtual tour application that uses custom panoramas in conjunction with Google's StreetView service. With StreetView, you can have 1 to n links at each particular location to move to, ...
3
votes
2answers
204 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 ...
1
vote
0answers
10 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 ...
1
vote
0answers
45 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 ...
2
votes
1answer
36 views

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), ...
0
votes
0answers
18 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 ...
3
votes
1answer
93 views

Find gap in / endpoints of linestring

I have a set of features of type linestring. I'm trying to polygonise the linestrings and assumed that they were closed (naive me :) ). Of course some were not closed and I'm trying to locate the gaps ...
1
vote
0answers
28 views

How can I automatically make new computings after I have modified some value in a field in ArcGIS Desktop?

I'm a computer programmer and I have no idea about geographic things. I have got a long algorithm with a lot of computings, computed from a previous computed field. There are 7-8 computed fields and ...
9
votes
1answer
3k views

How does ArcGIS Desktop calculate INSIDE point for Feature to Point?

Let me back up and say that from what I understand there are two common ways to calculate the centroid of a polygon in ArcGIS Desktop: Using Calculate Geometry on fields within the attribute table ...
4
votes
1answer
68 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. ...
2
votes
2answers
57 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!
2
votes
1answer
35 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 ...
1
vote
1answer
37 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 ...
64
votes
15answers
20k views

What are Definition, Algorithms and Practical Solutions for Concave Hull?

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 ...
2
votes
1answer
49 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 ...
1
vote
1answer
178 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 ...
1
vote
1answer
55 views

Counting number of points in 1 km grid covering surface of Earth?

I want to cover surface of earth with equal sized shapes and count number of points within each cell. shape of cell doesn't matters (triangle, hexagon ...), neither area, but equality of them is ...
2
votes
1answer
36 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. Any help would be appreciated.
3
votes
0answers
49 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. ...
2
votes
0answers
19 views

using MCA in GIS for suitability analysis

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. ...
1
vote
0answers
34 views

How to find the the boundary co-ordinates from a given set of coordiantes? [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 How to find the boundary co-ordinates from a given set ...
1
vote
0answers
50 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 methods ...
11
votes
2answers
1k 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 ...
3
votes
1answer
78 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 ...
2
votes
0answers
124 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 ...
0
votes
1answer
122 views

Determining if a Geodetic location is inside a polygon made up of Geodetic vertices

Suppose we have a polygon with Geotic vertices (Points A through E). Is there an algorithm that I can use that could determine If F is inside of it? In addition, what is the most efficient way to ...
8
votes
1answer
1k views

Grouping map points into fixed cluster sizes?

I have a dataset of 655 lat/long pairs which I'd like to split into about 100 groups. A group should have 5-10 pairs which are geographically close to each other. Dense groups should have more ...
1
vote
1answer
81 views

Error: Algorithm not found

I wrote the following code to start using QGIS APIs. in a very short script seen below, the "Error: Algorithm not found" is thrown and "print processing.alglist()" is showing none. Any idea why this ...
11
votes
6answers
3k views

How to find the boundary co-ordinates from a given set of 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 ...
0
votes
0answers
21 views

Tools to generate all the possible geometries meeting specific constraints

I have an area = 2d polygon (generally a 4-side shape). I would like to generate all the possible rectangles matching the following constraints: that fall within the surface of the area with a ...
5
votes
2answers
436 views

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

I've been wondering how the equations/algorithms behind buffering tools actually work?
2
votes
3answers
133 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 ...
1
vote
0answers
22 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 ...
2
votes
1answer
44 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 ...
3
votes
1answer
1k views

WGS point to WGS line segment (great circle) distance

How would I go about resolving this in C#? I have a line segment (great circle distance) defined by two Lon-Lat pairs (call them points A and B). A third point somewhere on the Earth sphere. The ...
0
votes
0answers
17 views

PRN (p-code) to Geocode Conversion

I think I have a unique situation. Client has a file containing the old p-code / PRN but can't relate this to a specific address and desires to move to a geocode orientation. Does anyone know if a ...
1
vote
1answer
32 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 ...
3
votes
1answer
157 views

Topographic Index - Why is upslope contributing area divided by downslope contour width and not upslope contour width?

In the Topographic Index calculation, a is the upslope contributing area per unit contour length. Is the "unit contour length" calculated from examining the contour widths of the downslope cells that ...
6
votes
3answers
148 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 ...
9
votes
2answers
331 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 ...
0
votes
1answer
2k 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 ...
5
votes
4answers
805 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 ...
1
vote
1answer
250 views

How to get Intersection point from two lines (coordinates)

I have tried for ages to find the algorithm for getting the coordinate of two intersecting lines from a given coordinate (latlong). As the picture below suggest. I have two coordinates (A and B). ...
2
votes
1answer
66 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 ...
3
votes
0answers
29 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 ...
7
votes
2answers
2k views

What algorithm should I use to remove outliers in trace data?

I have GPX traces and want to remove outlying observations. There are some route points that are impossible because it would require acceleration that the vehicle can not achieve. Are there good ...
0
votes
1answer
127 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 ...
4
votes
1answer
163 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 ...
6
votes
1answer
611 views

Breakline detection algorithms for LIDAR dataset

I'm searching for algorithms or open source tools I could use to detect breaklines from a LIDAR dataset; more specifically, from the terrain points of the dataset. At the moment the only thing I've ...
3
votes
3answers
130 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 ...