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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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6
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0answers
212 views

Packing squares polygons in a raster grid

In the green area of the raster I have to fit as many square polygons as possible, of three different sizes: 3x3 cell size 2x2 cell size 1x1 cell size With the fact that the approach should be ...
1
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1answer
55 views

Correlate two different zone system records

I am working with two data sets from different sources that represent the same phenomena and have a challenging point. Both data sets represent demographic attributed of the population [ person id, ...
0
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0answers
354 views

Geohash using decimal

I'm quite new to spatial data processing and got to work with some existing legacy data which isnt well documented. I see that in the SQL database geohash values stored along with lat and lon but they ...
1
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1answer
99 views

Finding crossing point between geodesic line and parallel?

Given a geodesic line (starting point and initial azimuth) is there an algorithm to find the longitude of the [first] crossing of a given parallel? I have already checked with Clairaut's constant ...
0
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0answers
52 views

Why many in-car navigation systems choose to go through the city center?

Most of the in-car navigation systems I've been using prefer to select an itinerary that goes through the city center, rather than getting around. And this is the case while the "Fastest" (not "...
1
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1answer
354 views

Split multi-geometries polygons

Is there is a way in QGIS (or SQL, ArcMap) to split multi-geometries in polygons automatically. I could do this manually (split features, split multi-part to single-part etc...), but this would just ...
1
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1answer
26 views

Merging tesselating regions depending on size?

I have the following regions marked up over map Each region has assicated statistical data. The problem is that sizes of these regions are very different. Some regions are very big and another ones ...
4
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1answer
1k views

Calculating the earth radius at latitude

This is an extension to this question: How do you compute the earth's radius at a given geodetic latitude? and to the Wikipedia page: https://en.wikipedia.org/wiki/Earth_radius#Geocentric_radius ...
3
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1answer
102 views

pgrouting - Choosing an algorithm with a predominance for a specific type of road

I would like to use one of pgrouting's algorithm to find the (shortest) path between 2 points with predominance for a specific type of road. To build the data I used the osm2pgrouting. Is there an ...
1
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1answer
552 views

Methods in Slope, Aspect SAGA calculations

Using this algorithm in QGIS I can choose between 7 methods, the default one being by Zevenbergen & Thorne 1987. What's the difference between them and can I just use the default one without ...
2
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1answer
153 views

Calculating a baseline shoreline from multiple surveys

We are trying to calculate a average shoreline position from a collection of shorelines dating from the 1880s to the present, the purple lines shown on the map below: We want to create some code that ...
3
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2answers
537 views

Algorithm for clipping large volume of points to irregular geometries?

I am currently using a home-brewed-hacked-together method for clipping a large number of points (~500k, could be more or less depending on the day) by a circle with a fixed radius. The output is a ...
0
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1answer
106 views

Python arcpy recursive function problems

I'm trying to implement an algorithm using values from an arcpy module. Here is my equation written into code. I need for the initial value of the variables St and Yt to start off at zero. After the ...
2
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1answer
97 views

Formula for rotating half degree square map/data frames in projected coordinate system so that they look straight?

I am currently developing a map series using ArcPy with ArcGIS Pro. I am not using the Map Series functionality for this because I need to have lots of control over what is on each map sheet, and ...
2
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1answer
473 views

Algorithm or command line tool to decimate point cloud of terrain points?

I need to take a larger (more dense) than needed list of lidar survey points (longitude, latitude, and elevation) for terrain definition and decimate it based on a 2 dimensional grid. The idea would ...
2
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0answers
112 views

QGIS Projective Transformation Algorithm

I would need to know something more about the algorithm that Qgis (Georeferencer Plugin) uses to georeference with projective algorithm. I have tried to reproduce your results using other software ...
1
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2answers
129 views

Writing an algorithm for filtering spatial data based on the local coefficient of variations in R

I'm trying to write an algorithm for filtering spatial data based on the local coefficient of variations within a search radius. If the number of points with CVs over 25% equals to the total number of ...
9
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2answers
1k views

Finding Similar Map Paths

I'm looking for an algorithm which, when given a particular route on a map with attributes such as incline/distance/shape/etc, can find a route which is similar (in terms of the attributes) but starts ...
1
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2answers
266 views

How can I calculate community populations with CIESIN / Facebook's new High Resolution Settlement Layer data?

Facebook's Connectivity Lab and the Center for International Earth Science Information Network (CIESIN) have released map data which offers unprecedented resolution in terms of population mapping. By ...
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 ...
2
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0answers
156 views

Finding adjacent MGRS blocks/grids?

My requirement is that, say I'm given a MGRS grid (100mX100m), I now need the IDs of all the 8 MGRS grids around the one that was given. One way that is being suggested is as follows. Compute the ...
13
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1answer
268 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: ...
2
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1answer
272 views

Algorithm for Cost Connectivity tool of ArcGIS Spatial Analyst?

For the Cost Connectivity tool in the Spatial Analyst toolbox, what is the algorithm used to compute the minimum spanning tree? The ArcGIS website includes a general description of how the cost ...
16
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3answers
955 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 ...
0
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1answer
49 views

Segmenting a sequence of GPS readings into coherent 'GPS Tracks'

Consider the problem of wanting to extract semantically coherent 'tracks' from a sequence of GPS readings. In this context, I mean 'semantically coherent' to be arbitrary and subjective. For example, ...
1
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1answer
42 views

Iteration algorithm over geometric attributes of shapefile with arcpyscripting

I am trying to create a separate skyline shapefile for every feature ID I have in my point file by splitting them into multiple files. The code works fine, except splitting them into multiple ...
5
votes
1answer
858 views

LiDAR dataset which is benchmarking for testing classification algorithms?

Is there a publicly available benchmarking database of classified (labeled) LiDAR data? For example, where each point is classified as ground, vegetation, building, road, water, etc? The point clouds ...
2
votes
1answer
76 views

How does a vector buffer work?

I am trying to code a type of buffer and I tried to find the source code of the buffer function in the ArcGIS and QGIS files in order to understand how it works in depth when it comes to creating ...
2
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1answer
1k views

Calculate surface area from horizontal area and angle

I have a shapefile includes polygon features of tilted solar panels and I used "Calculate Geometry tool" in ArcGIS to find out the projected area of solar panels (horizontal area). I am looking ...
0
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2answers
459 views

Map from point-data to region data in Python

I have a dataset that lists entities per district - where district is a named shape that exists on a map. I have a different dataset that contains entities of the same type, only instead of being ...
5
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2answers
261 views

Investigating PostGIS functions to see what they are doing?

Let's say you have a function like ST_Distance and I want to know how it works. The docs don't say much at all, how do I go about debugging this or figuring out how it ticks.
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2answers
4k views

Distance calculation using ST_Distance

I am trying to calculate the distance using the ST_Distance function in the postgres database. I am using following query: SELECT ST_Distance( ST_GeogFromText('SRID=4326;POINT(52.3551151038034 4....
2
votes
3answers
169 views

How to find the “first” intersection of a line with anything else

I am trying to find the first intersection of a line with anything else. By first intersection I mean the first intersection, if you follow the line in its direction from start to end. Check the ...
0
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1answer
192 views

Algorithm for all intersecting geometry parts

I'm trying to understand the ArcGIS "union" method so I can replicate it with an algorithm using Python and Shapely. I do not want the cumulative intersection of all features where all of them ...
1
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1answer
215 views

Resampling Raster

So I was thinking about a method that would allow me to essentially get the same resolution as a 3 meter DEM but with the size of a 30 meter DEM. As most GIS people know, 3 meter DEMs tend to be ...
0
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1answer
2k views

Get distance in meters between lat/lng coordinates, divided in North and East direction

I've got 2 couples of lat/lng coordinates and I would like to get distance between them in meters, but divided in X (east) and Y (north) directions. I've found this function in a Stack Overflow ...
0
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1answer
87 views

How to get snapped points on the line with v.clean?

I followed the answer posted by @Micha in splitting a lines layer using points, because my points were not exactly on the line, I used v.distance and v.patch described in the answer. Then I tied to ...
0
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0answers
406 views

Splitting polygon into three equal parts using NetTopologySuite and C#?

I have a polygon, I want to split it into three equal parts, I have a scenario as below: User must select a vertex on polygon User must add direction to start split on Based on the node and direction ...
1
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2answers
136 views

Getting flow directions of people moving

I'm creating an application which finds out the direction people are walking in, Gives the direction in which majority of people are walking and the people going in the opposite direction. For ...
24
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2answers
706 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 ...
4
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1answer
2k views

Understanding Contraction Hierarchies

I'm very interested by understanding how Contraction Hierarchies algorithm works. I have found this page : https://www.mjt.me.uk/posts/contraction-hierarchies/ and read a lot of stuff. I understood ...
1
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0answers
48 views

Errors executing certain algorithms in QGIS Processing Toolbox? [duplicate]

When I execute certain algorithms in Proccesing Toolbox, for example "Convert polygon/line vertices to points" I get the following error: Algorithm Convert polygon/line vertices to points starting.....
1
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0answers
108 views

How to convert building outlines to Polygons?

I have line vector layer which contains contours of buildings in the form of separate segments. I want to convert lines to polygons (QGiS 2.17) but it doesn't work. I'm trying to solve this problem ...
1
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0answers
60 views

walk me through tdoa [closed]

I'm working on a TDOA application. This is just something in my free time to see if my hardware can accurately do it and it sounded like a cool challenge. Regardless if it looks possible or not, I'm ...
1
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1answer
379 views

Regrouping points together based on a sum

I have a vector layer containing points. Each point has an attribute called 'number of houses'. I want to dissolve this vector layer in many areas, each area must contain between 643 and 653 house and ...
3
votes
1answer
4k views

How To Properly Implement a Bounding Box for Shapely & Fiona?

I am trying to spatially analyze two layers within same GDB file using Python / Shapely. Another user was kind enough to give me a procedure to go by in trying to reduce the number of senseless ...
1
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0answers
60 views

Spatially Analyzing two layers within same File Geodatabase using Python / Shapely?

I'm using a nested for-loop to do Shapely analysis between two Python lists created via two pre-reads of the same GDB file. One list contains all the features of a particular layer while the other ...
2
votes
0answers
526 views

Wrap the set of points to the minimum polygon

Given I have a set of points which represents the circles which are intersected. As result I'm trying to receive the boundary which represent the polygon which wraps all circles. Please take a look ...
1
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0answers
512 views

Algorithm for converting from projected coordinate system to geographic one using Helmert transformation

I have a data in projected coordinates system and I need to convert them to WGS84. I know the parameters of position vector transformation and I know the projection details of my projected coordinate ...
9
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0answers
2k views

Is it possible to stop an algorithm midway through processing in QGIS? [duplicate]

This question come about do to an annoying though infrequent issue I have been having in QGIS. On occasion, I will begin processing a tool that will take some time to run but realize midway through ...