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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Translate Orientation from Sensor data to Geo location

I am tracking a device that might loose GPS signal then and there. And when the GPS signal is too low, I should use the accelerometer and Gyroscope sensors data to guess which way they should have ...
Kevin Peter's user avatar
7 votes
3 answers
2k views

Determining whether polygon crosses the antimeridian

I'm working on a system that uses bounding boxes as a fast first check for a point-in-polygon filter. My current naive implementation (just taking the min/max lat and long for all points) fails on ...
nrabinowitz's user avatar
6 votes
0 answers
330 views

Speeding up execution of PyQGIS algorithms

I don't understand why if I do "manually" some algorithms I get results much faster than when I insert the same in a PyQGIS code (with the same input). This happens, for example, with the ...
Sara Gaudio's user avatar
6 votes
0 answers
2k views

QGIS: Release file lock on file used in a processing algorithm at the end of script

I am using runalg (qgis:joinattributesbylocation) on two QgsVectorLayer objects. At the end of my script I'm trying to delete all the files created during the script. I can delete everything except ...
David M.'s user avatar
4 votes
1 answer
327 views

Using memory layer as input with processing runalg in PyQGIS

My first processing runalg creates a memory layer as output. I need to use this layer as the input for the second runalg. #first processing.run("qgis:fieldcalculator", { 'INPUT': '...
Kajo's user avatar
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4 votes
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462 views

Create equidistant points along line network?

I am trying to create points at every X meters along a set of lines that represent a network. As suggested in QChainage doesn't place points evenly along dissolved lines I managed to this ...
Albert's user avatar
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3 votes
0 answers
50 views

What is the name of the popular buffer algorithm?

There is a well-known algorithm that I believe is used for the "buffer" function in some GIS libraries and applications. I have a vivid memory of reading the paper that describes the algorithm and ...
Michael Geary's user avatar
3 votes
0 answers
41 views

How does iterative clip decide its processing order?

I have a fishnet grid which I use to iteratively clip several large shapefiles. The output of the clipping tool results in the selected output filename plus an incrementing suffix (_0, _1, _2 ... _n). ...
B.Quaink's user avatar
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3 votes
0 answers
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need Matching Algorithm which takes graph Topology into account

Problem: I have a problem (illustrated below) with matching two datasets. On the left I have a GIS containing drain network data (in blue), including diameter, length and topology information (from- ...
Mr_Robinini's user avatar
3 votes
0 answers
2k views

Algorithm to simplify a Polygon/Series of Points to a given number of Points

I have a polygon (or let's call it just a series of points). I want to simplify it (reduce the amount of points) to a given number of points. Currently I use Douglas Peucker and try to guess the ...
Robin's user avatar
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0 answers
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Optimum Path finding (for Cross Country Movement) using TIN

I am working on path finding algorithm (using A*) for cross country movement (not for road movement) on map using grid based approach. Algorithm supports path calculation considering slope of terrain. ...
Keyur Mahajan's user avatar
3 votes
0 answers
308 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? ...
Justin Dearing's user avatar
3 votes
0 answers
81 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 let'...
pgf's user avatar
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3 votes
0 answers
346 views

Placement of a fixed-radius circle on a sphere to maximize point containment

There are many papers on the "Circle Placement Problem" in 2D Euclidean space, but I haven't been able to find any papers discussing this problem on the sphere. The problem is: given a set of points ...
bnsmith's user avatar
  • 131
2 votes
0 answers
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Existing Algorithms for label placement with callouts

I am thinking to answer the question here: Label placement with callouts in QGIS. I want to implement a kind of algorithm in python that will create 2 different columns [X and Y] that will be the ...
eagleadmiral's user avatar
2 votes
0 answers
73 views

Seeking algorithm for polygon straightening

I have a polygon that looks like this: I want to get a result that ideally looks like this: The best that I can come up with is a polygon simplification using shapely in Python: Which algorithm ...
Марина Лисниченко's user avatar
2 votes
0 answers
35 views

How to colorize hierarchically-ordered polygons?

I have to implement a solution for coloring a lot of polygons that are derived from a hierarchically-ordered dataset. The dataset can be compared to a family tree in terms of hierarchy. Most of the ...
sicadu's user avatar
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2 votes
0 answers
45 views

Output singlepart features by default for tools and algorithms in QGIS

In QGIS, many algorithms and tools return multipart geometries. For further processing, a conversion Multipart to singleparts is necessary. This is a bit cumbersome. To make just one example: when ...
Babel's user avatar
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2 votes
0 answers
49 views

Connecting points with Z values to lines where the Z values are retained in the nodes of the resulting line

I have interpreted seismic data as xyz-points (about 23 cm lateral resolution). They are not really ordered but rather a simple list of coordinates. One file contains multiple seismic "lines"...
Sascha K.'s user avatar
2 votes
0 answers
43 views

Are there any mass-preserving raster projection algorithms?

Raster maps (e.g. as a GeoTIFF) can be reprojected using tools like gdalwarp. While these tools do a decent job to project images, they are not truly mass-preserving, i.e. the total sum of the values (...
p.w.bogaart's user avatar
2 votes
0 answers
36 views

Determine how regular a set of points is?

I'm trying to cluster some gps data to accurately determine stop points for vehicle movements on a testing grid. I know the points they stop at are regular/closely match points on some defined grid of ...
jf433's user avatar
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2 votes
0 answers
150 views

Algorithm to find low/high atmospheric pressure systems in gridded raster data

What's the commonly used algorithm for finding center positions and values of low/high atmospheric pressure systems in gridded raster data (GRIB/NetCDF/GeoTIFF)? First I tried a naive approach to ...
zakjan's user avatar
  • 204
2 votes
0 answers
864 views

Doing TIN Interpolation in QGIS

I want to do TIN Interpolation on a layer but when I fill all the fields with the right data (vector layer, interpolation attribute, extent etc) the algorithm does not run and shows me this message: ...
Διονύσης Χρι.'s user avatar
2 votes
0 answers
70 views

Efficient random access into rasters for hydrological analysis

I'd like to implement an algorithm to extract Strahler Streams as geometric lines from a predefined stream raster. I've done this using GDAL by walking across the rasters from the outlets or at the ...
Rich's user avatar
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2 votes
0 answers
74 views

Multiple centroids of complex outline polygons by recursive buffering

How can I algorithmically determine multiple centroids for overlapping (dissolved), very irregular regions representing canopy outlines? This is effectively a forestry issue. The context is that I ...
Ivan Heitmann's user avatar
2 votes
0 answers
112 views

Calculate where a geodesic line crosses a meridian

Given a geodesic line between two points with known coordinates on a sphere, is there an easy way to calculate or approximate where this line crosses a specific meridian? I want to calculate where ...
user3170702's user avatar
2 votes
0 answers
78 views

Splitting linestrings based on their curvature

I'm looking for a method to split linestrings based on their curvature, more precisely if part of them could be considered a street corner. For example in the screenshot below, I'd need to split the ...
Jukurrpa's user avatar
  • 331
2 votes
0 answers
79 views

Getting minimum distance of points with scalable algorithm

I have a number of geographical coordinates with latitudes/longitudes: id | name | lat | lon 1 | New York | 40.730610 | 74.0060 2 | Philadelphia | 75.1652 | 39.9526 3 |...
ulima2_'s user avatar
  • 129
2 votes
0 answers
196 views

Simplifying Multiple neighbouring Polygons, removing gaps and overlaps

My main goal is to simplify multiple polygons, avoiding overlaps and gaps between them. My initial approach was: Find intersections for each polygon so that I end up with an array of polygons, each ...
fhristov's user avatar
2 votes
0 answers
46 views

Seeking method for determining survey points?

I'm trying to write software to create a topographic map, my goal is to select several points of interest and create a minimal mapping that is inclusive of the points and interpolates the topography. ...
Schalton's user avatar
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2 votes
0 answers
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Algorithm "qgis:difference" returns multiple heterogeneous outputs

I use the qgis:difference algorithm but it returns multi-type outputs. Sometimes it's a QgsVectorLayer but sometimes a str such as : output_.... My question is : when the algorithm returns an empty ...
dmjf08's user avatar
  • 1,263
2 votes
0 answers
92 views

How can I share with other users a preconfigured algorithm?

I´m creating a process in QGIS, and I make it work automatic. But, I´ve used a preconfigured algorithm in order to avoid selecting shapes every time you use the process. So, is there any way I can ...
Alejandro garcia's user avatar
2 votes
0 answers
305 views

GIS Clustering with drawing predefined square area around points as cluster boundaries

I have a layer of points and I would like to create clusters where a predefined square area of 5km by 5km is the boundary for the cluster. Is there a way to iteratively draw square polygons around ...
Primož Dolžan's user avatar
2 votes
0 answers
46 views

How to take all active layers as input for an iterative algorithm?

I have a whole list of different layers I want to do a iterative clipping algorithm on. (Batch processing is not an option as the 'iterate' button is gone.) This is a follow up on my question here. ...
B.Quaink's user avatar
  • 455
2 votes
1 answer
183 views

Yen's or Eppstein for path with intermediate destinations which are dangling nodes

I'm trying to find a shortest path algorithm (which does not need to be optimal) for a path with intermediate destinations. Consider the following case: One wants to go from A to Z and in between ...
i.i.k.'s user avatar
  • 1,343
2 votes
0 answers
47 views

How to Make automatic classes with algorithm in qgis modeler?

I have 1 column of numeric data in one attribute table of a layer made of points. I want to regroup this data in classes (style) with the Qgis modeler and each class must have a specific lenght that ...
Marc Robin's user avatar
2 votes
0 answers
203 views

Seeking algorithm behind End Point Rate (EPR) to calculate movement of shoreline over period of years?

I am analyzing the shoreline change over a period of 20 years(1998-2018). I have following data: digitized shorelines of 1998, 2003,2008,2013 and 2018 one common baseline for all shorelines transect ...
Anuja Negi's user avatar
2 votes
0 answers
176 views

QGIS processing algortihm crashes in python console but works manualy

I am loading two layers from PostGIS database and I am trying to run 'qgis:intersection' algorithm with them. Execution of the algorithm through the python console initially works but crash after 2-3%....
D.Betsov's user avatar
2 votes
0 answers
141 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 ...
Jartieda's user avatar
2 votes
0 answers
274 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 ...
user1472309's user avatar
2 votes
0 answers
1k 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 ...
kirill.buga's user avatar
2 votes
0 answers
913 views

Is there an R package for finding the maximum-area rectangle in a non-convex polygon?

Does anyone know if there is an R package out there with an algorithm which finds the largest rectangle within non-convex polygons? I have Googled, searched the R Sig Geo archives, and looked here on ...
Tiernan's user avatar
  • 396
2 votes
0 answers
66 views

Creating 30 areas with equal amount of road in irregular polygon using MapInfo?

The result should be something like this just more polygons. Does anyone know about a tool, which given a table, can create a number of polygons which will divide the tables object into, for ...
Tengnagel's user avatar
2 votes
0 answers
258 views

Application of a Piecewise Logistic Function to Extract Seasonality Metrics

I am working with 16-day MODIS EVI (satellite) data and I want to fit a Piecewise Logistic Function through my 23 EVI data values. The following formula is for the Piecewise Logistic Function: y(t)= [...
Xu Teo's user avatar
  • 155
2 votes
0 answers
911 views

How to check if a polygon contains another polygon in OL3?

Is there any possibility to check if a polygon is contained in another polygon in OL3? I noticed there is a couple of methods in ol.extent e.g. ol.extent.containsExtent(extent1, extent2). But this ...
Geod Master's user avatar
2 votes
0 answers
151 views

Calculate distance in point collection algorithm

I've got collection of points which are sorted by x,y and distance between n and n+1 (array of objects [{x:0,y:0},{x:1,y:1}....] I would like to calculate distance between all points (point 1 distance ...
Krystian's user avatar
  • 861
2 votes
0 answers
282 views

Adding nodes into graph using QGIS?

I'm new to qgis and in here I want to find a path between two selected points on the map(Roads-vector layer). The points are selected by the user, using mouse clicks. So here I used the astar ...
Ramanayake's user avatar
2 votes
0 answers
118 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 ...
NKK's user avatar
  • 21
2 votes
0 answers
170 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 ...
Jordan Arsenault's user avatar
2 votes
0 answers
2k views

Help with Shortest path Algorithm for enormous bus routes database

I am building a bus routes map for Chennai. I use Postgis. In our database we have one table having all the routes along with unique ids given for them. Second table comprises of bus stop names with ...
Varshini's user avatar