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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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 ...
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QGIS doesn't load up after "Setting up the GUI"

After the flash image loads "Setting up the GUI", it disappears and QGIS doesn't continue to run. It runs sometimes when I try to open QGIS through C:\Program Files\QGIS 3.22.6\bin\qgis-...
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4 votes
2 answers
228 views

Detecting and making all connected lines in the same direction in QGIS

I have a list of straight roads segmented which has a unique "ID". I would like to detect connected lines in the road network and make them in the same direction instead of reversing them ...
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2 votes
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Zip output of QGIS Processing Algorithm

I want to make a script which processes some algorithms with multiple layers as inputs outputs some results in QGIS project then save the layers as zip files in a specified folder I have not been ...
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Building squaring using JGiscoTools java lib

I`m new in Java and trying to use JGiscoTools java lib for building squaring from .geojson file according to algorithm in this document I've tried to use class Squarring of the algo module, but doesn`...
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2 votes
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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 ...
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Passing selected layer-feature inside QgisAlgorithm (in code)

In our algorithm, we do three steps: call Algorithm A AlgoA, takeResultLayer into lyr from AlgoA output, for each feature of lyr we want to run Algorithm B AlgoB . Code of my processAlgorithm looks ...
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4 votes
2 answers
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Processing algorithm as expression in QGIS

I would like to be able to set an expression as the default value of an attribute (in layer properties-->attributes form) which uses an algorithm from the QGIS toolbox. In this case, the algorithm ...
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2 votes
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PyQGIS 3: Cannot Pass Memory OUTPUT To Next Processing Algorithm As INPUT

I am attempting to convert some ArcGIS arcpy command-line scripts to PyQGIS and am running into a problem working with memory layers. The script takes several vector files as input and progresses ...
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3 answers
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Finding largest circle which entirely included in multipolygon and not containing any point of points layer

I have two layers*: 1 MultiPolygon (the complex green features) 1 MultiPoint (many thousands of yellow dots) How can I efficiently find the largest circle (center coordinates + radius) which is both ...
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Seeking algorithm other than Convex-Hull to avoid overlapping polygons

I want to draw polygons with no overlap, based on sets of points. If I use Convex Hull algorithm to deduce the boundary polygon, it's pretty obvious that the resulting polygons WILL overlap. Is there ...
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Null standard errors in multiscale geographically weighted regression

I'm currently conducting an multiscale georgraphically weighted regression using the official python based package by Oshan et al.*. However, i ran into a slight problem. Whenever an explantory ...
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Algorithm for least cost path used by SAGA

I have to calculate the least cost path between two points and found this tutorial: https://dges.carleton.ca/CUOSGwiki/index.php/Cost_Path_Analysis_of_Mars_using_SAGA. That's why I also want to use ...
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Least cost path algorithm in SAGA?

I'm very new to this topic. I have to calculate the least cost path between two points for a school project and found this tutorial: https://dges.carleton.ca/CUOSGwiki/index.php/...
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2 votes
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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"...
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2 answers
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How can I cover an AOI with a subset of image extents?

I’ve been experimenting with a problem that I have not found a friendly and simple solution for yet. Curious to know if any of you have already solved this problem. Given a AOI and a set of image ...
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5 votes
3 answers
180 views

What is algorithm name for "Count Points in Polygon" using PyQGIS?

I want to count points in polygon, using PyQGIS. When I check the documentation, I find the description of the {parameter_dictionary}, but not the algorithm name which must also be provided. What is ...
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Selfmade XYZ Data can't be loaded by GRASS Algorithms

I'm trying to use my own measurement data for multiple GRASS algorithms in QGIS. When I use a 1m raster from the internet everything works perfect. But if I use my own data I get an error stating that ...
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2 votes
3 answers
218 views

Simplify a branching line string

I have been working on developing a GeoTools function to create a central label line for polygons. The idea was to grab the skeleton of the polygon and use that to place my label, however it turns out ...
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"Rounding" GPS coordinates based on uncertainty range

A stationary GPS receiver will produce a random cluster of coordinate points around its actual location. I can look at previous coordinate readings and apply various algorithms to find the "...
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148 views

Shortest-path algorithms used in Networkx: what about points not near nodes?

I am new to Networkx, but am I right that Dijkstra's is the algorithm Networkx uses by default? From what I understand, Dijkstra's algorithm traces a shortest path between two nodes on a graph. What, ...
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1 vote
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Automatically create points based on algorithm

I have a shapefile with points representing the sightings of different bird species on different dates (in ArcMap 10.4.1). I now have to create a new shapefile with points for bird territories. A ...
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1 vote
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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 (...
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2 votes
0 answers
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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 ...
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Genetic algorithm based microphone array placement for optimum acoustic coverage [closed]

I am trying to find the optimal location for the placement of the microphones. I want to reduce the no of microphones place on the given area of interest. I want to use minimum no of microphones to ...
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33 views

Does opening QGIS multiple times slow down an algorithm?

I have to run an algorithm (SEBE, from the tool UMEP) around 30 times, everytime taking a couple of minutes to a few hours. Unfortunately, it seems like it can not be run as a Batch-process, so I ...
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2 votes
1 answer
24 views

QGIS: No values in field after creating spatial index

I want to join a vectorlayer with a grid using the algorithm "join attributes by location (summary)". It took hours to execute, but it worked. Then I found This thread which told me I have ...
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  • 157
1 vote
1 answer
263 views

Problem when running the Clip Raster by Mask Layer - Layers were not correctly generated

I need help, this is for my Final Year Project. Yesterday before I did something on my QGIS, I can run the mask layer but suddenly after I followed a tutorial on youtube on how to do 3D Map, I cannot ...
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2 votes
0 answers
85 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 ...
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  • 204
-2 votes
1 answer
60 views

Creating a loop itinerary

I am trying to find a way to create a loop itinerary. For example, I know my starting position, and I want to walk some distance and come back to my starting point. It's quite easy to find itinerary ...
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2 votes
0 answers
387 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: ...
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1 vote
1 answer
121 views

What algorithms can be used to create a DTM from a DSM TIFF file i.e that will reduce or exclude features such as trees and buildings

I am using Python and QGIS. I have obtained - purchased - a 1m DSM photogrammetry data file - a TIFF. I could purchase a DTM from the same company, but they are 5m grid, and so they lose some data I ...
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1 vote
1 answer
135 views

Landsat footprint artifacts in statewide CCDC map

I have produced a map for New York State using CCDC as implemented in google earth engine. The map counts the number of disturbances for each pixel occurring between 1990 and 2019 (black = 0 ...
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86 views

How to define the spatial distance ε for EDR and LCSS similarity algorithms?

Let's assume a dataset with human trajectories like Geolife. I want to measure the similarity of two random trajectories from this dataset using the EDR or/and LCSS algorithm(s). I wonder, which ...
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3 votes
1 answer
1k views

What is the algorithm that Shapely used to check if two polygons intersect?

What is the algorithm that Shapely used to check if two polygons intersect? from shapely.geometry import Polygon p1 = Polygon([(0,0), (3,0), (3,1), (1,1), (1,2), (3,2), (3,3), (0,3)]) p2 = Polygon([(4,...
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  • 33
3 votes
1 answer
127 views

Get field list of input layer using @alg decorator

I'd like to write a simple algorithm to sum up a numeric column in an input vector layer. I can't connect the FIELD input to the SOURCE layer. I tried to add 'parent' parameter but it is unknown ...
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  • 6,722
2 votes
0 answers
36 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 ...
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1 vote
1 answer
483 views

Does a common algorithm exist to find the midpoint of a linestring by distance within a coordinate system?

Recentl I needed to find the mid-point of a linestring. I work with java/Scala so I naturally reached for the JTS library but couldn't find anything in there for doing this. I implemented an algorithm ...
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2 votes
1 answer
48 views

Range search: Identify points in intersecting circles

I am trying to identify points in two intersecting circles. The points are only in the first circle $O_1$. In many cases, the node density in the circle is not uniformly distributed. The radial node ...
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1 vote
0 answers
27 views

Reshape nearby polygons so that they share a common border

I am looking for an algorithm for reshaping polygons that are close to each other. Given 2 polygons that have certain parts within proximity E reshape the polygons such that they share a common border ...
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0 votes
1 answer
96 views

PyQGIS algorithm qgis:joinattributesbynearest not found

After re-installing Windows and QGIS 3.14 it seems like some PyQGIS algorithms are not working. For example: processing.run("qgis:joinattributesbynearest", options) gives core....
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1 vote
1 answer
252 views

Fully cover polygon with circles of fixed radius? [closed]

I have some detailed polygons I want to cover by generating points buffered to 4km radius. How do I determine the best way (or even a decent) way of covering the polygons completely with minimal ...
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3 votes
1 answer
162 views

QGIS algorithm to copy vector layer with only selected fields

I am trying to find out if there is a way - or even an algorithm in QGIS - that enables you to effectively create a new feature layer that is a copy of an original layer but with only a selection of ...
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1 vote
4 answers
146 views

Algorithm to convert DN values to Radiance

Which algorithm should I use to convert DN(Digital Number) values to radiance. There are many different algorithm that I found, there are 3 for now (based on youtube, article, usgs website). My aim is ...
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0 votes
0 answers
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How can you completely cover the surface of a raster with circles where the radius of the circle is the raster value at its centroid?

This is more of an algorithmic/math problem, but I was wondering if someone could point me in the right direction. There's the common problem of covering a surface with circles of equal sizes, but ...
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1 vote
0 answers
60 views

Lasso selection performance

I'm the author of Leaflet plugin for lasso selection (leaflet-lasso). The lasso polygon consists of drawn mouse coordinates converted to lat/lng. When mouse is released, all map features are checked ...
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1 vote
0 answers
158 views

Error in Built Up area Classification using Landsat 8 in google earth engine ( SVM, RF and Cart)

I am using Earth Engine to Classify an area using supervised classification with a combination of reflectance bands and indices. The built-up area gets mixed with fallow land (bare soil) and I have ...
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  • 11
1 vote
2 answers
268 views

QGIS - Can't select Inputs for Select by Location algorithm in Graphical Modeler?

All the other questions I've seen so far are a step ahead of me. I've defined an Input for a vector layer, and am trying to use the Select by Location Algorithm. I typed the name of my Input, but the ...
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3 votes
1 answer
315 views

How to use a Processing Algorithm in a expression function used in a Geometry Generator (Points Along Lines "on the fly")

I want to use the Processing Algorithm, pointsalonglines, in the expression function used in Geometry Generator. This is because I want to create points "on the fly" along my line and in a ...
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1 vote
0 answers
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LiDAR data denoising algorithm complexity

I want to remove outliers (noise) from LiDAR data. Currently I'm using the same algorithm as LAStools: The LAStools software version 171215 implements a straightforward outlier removal ...
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