# 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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### Difference between ST_Simplify function in PostGIS 3.0.0 and PostGIS 2.5.3

Faced such a problem (or maybe it's a bug). I get different results when using the ST_Simplify function in PostGIS 3.0.0 and PostGIS 2.5.3. There are source data that are simplified by using a query: ...
19 views

### How to find similar GPS tracks considering timestamps?

There are around 300 users tracks per day with about 4k points in each with 10s time interval. I'd like to find similar tracks considering location and time. The tracks are similar if it can be ...
42 views

### How to store / what algorithm to use to find closest points from a given set of points to a polyline layer

I have a polyline layer and a points layer with features that are nearby the polylines. For the latter I want to find the closest points on the polylines (as existing vertices or new-created vertices ...
44 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 ...
34 views

### Find minimum number of polygons connecting two points

Given GIS data of polygons and two points, is there a way to find the minimum number of polygons you need to traverse to walk between the two points? Even an approximate approach would be fine for my ...
47 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 ...
48 views

### Perform Tile Index on Newly Created PDFs using PyQGIS

The python code below successfully performs the tile index algorithm on all PDF files stored in sub-folders named !pdf's within my V:Drive. A list of all paths to each PDF exported from QGIS is ...
36 views

### Getting Omniscape analysis ERROR: LinearAlgebra.LAPACKException(3)?

I am currently running landscape connectivity analysis with Omniscape, but I get this error : ERROR: LinearAlgebra.LAPACKException(3) Stacktrace: [1] chklapackerror at /builddir/build/BUILD/julia/...
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### How to calculate line complexity index

I'm wondering if there is any suitable algorithm that can I use to calculate line complexity index (or indicator)? By "line complexity" I mean how many bends (direction changes) that line contains and ...
20 views

### Drawing equal paths from geographic points?

I have 10'000 geographic points (POS), 10 salesmen, and one starting point. To avoid discrimination between salesmen, everyone should travel the same distance and the same number of points of sale. ...
43 views

### Calculate position to put box into another container?

there has a big box, and the big box already contains many small box, then should place a new small box into the container. How do I calculate a big enough space to place the small box? There ...
99 views

### Splitting Streets to Create Polygons?

I have a need to take all the streets belonging to a certain area (in OpenStreetMap) and split each street by each other and form polygons from the segments that result from the split operation. I do ...
35 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 ...
160 views

### Adding new attribute field to processing output algorithm in PyQGIS?

I have a processing script that will carry out a selection by expression of the input layer, then do a join attributes by location with a join layer. The next stage will be to add a new field and ...
27 views

### qgis:deletecolumn in QGIS 3 graphical modeler

I want to use the algorithm qgis:deletecolumn in a graphical modeler. How do I have to fill the case Fields to delete : ["field1","field2"] "field1","field2" field1,field2 [field1,field2] And is ...
55 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 |...
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### 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 ...
149 views

### Performing isochrone in PostGIS by pgRouting?

In pgr_drivingDistance for isochrones the person who answered, missed to say the explanation of the answer about what function used by him to get the output for isochrone. I want to do the same but I ...
46 views

### What is the complexity (big / little o) of the ArcGIS watershed delineation algorithm? [closed]

I'm curious about the complexity, in terms of Big or little O notation, of watershed delineation algorithms that are implemented in ArcGIS. I imagine that these will be dependent on either the size ...
33 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. ...
116 views

### How to create equidistant points along lines (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 ...
578 views

### Client-Side Polygon split

I wanted to know if there is a way to split a polygon using JavaScript. So I have a web map which uses Leaflet API, and the user needs to cut polygons which are shown in the map using a straight line. ...
82 views

### Seeking Python implementation of contiguity constrained clustering?

I'm looking for an example of Python implementation of contiguity constrained clustering algorithm. The task I want to perform is to reduce the number of administrative zones by grouping them into as ...
150 views

### QGIS Python AttributeError object has no attribute 'pushVersionInfo'

I am unable to use almost all of the processing toolbox features in QGIS. I keep getting the following Python error across multiple algorithms: AlgorithmDialog.py", line 208, in runAlgorithm self....
33 views

### Algorithm(s) for Sensor Footprint at limbs

Is anyone aware of algorithm(s) that have been developed for computing remotely sensed image footprints that handle body limbs? The limb is the edge of the body / atmosphere where only the blackness ...
33 views

### 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 ...
175 views

### Match linestrings using Fréchet distance

I have two datasets of roads (both in WGS84). One has nicely digitized geometries, but lack some of the attributes and the other has heeded attributes, but digitized terribly. I want to transfer ...
39 views

### How is IDW raster formed?

IDW algorithm says that it makes a grid and assigns value to each point in grid depending on the distance of separation. From this definition, it looks like the output is set of equally spaced points. ...
116 views

### PYQGIS 3 Using the ouptut from GRASS v.distance algorithm

I have a script which is trying to run v.distance on two existing shape files, buildings.shp which containing some polygons and singleasn.shp which contains a single point. This will be run from the ...
219 views

### What algorithm is used by the \$geowithin operator of Mongodb

MongoDB can perform geospatial query such as finding restaurants inside region with the operator \$geowithin. For example: db.places.find( { loc: { \$geoWithin: { \$geometry: { ...
367 views

### Finding algorithms of QGIS commands?

I'm looking for the algorithms (the math) used by QGIS but I can't find any documentation about it The ones I'm looking for are: Minimum bounding geometry (convex hull) Clip a polygon by a ...
46 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 ...
200 views

### Get progression bar into PyQGIS 3 standalone script

When I run a treatment inside QGIS with Processing toolbox (native algorithms) I get a progression bar : Is there a way to use this percentage inside a standalone PyQGIS script? I searched in the ...
42 views

### Creating decision rules on pixel level in time series layer in R? [closed]

I am using Landsat 5, 7, 8 images and RStudio. My goal is to compute the disturbance in a given area using the Vegetation Change Tracker (VCT) algorithm. I would like to ask you if you could provide ...
420 views

### Run pyQGIS algorithm on selected features in layer

I try to run algorithms on layers but only on selected features with QgsProcessingFeatureSourceDefinition in a loop and then write the result with QgsVectorFileWriter : layer1 = QgsVectorLayer(path1, ...
223 views

### PyQGIS processing: Overwrite not possible

I have a QGIS plugin that runs the v.clean algorithm two times (first time snap, second break) on a chosen layer: output = self.dlg.directory.text() params_snap = { 'input' : input, ...
172 views

I try to run a QGIS plugin in QGIS 3.4 that uses processing to execute algorithms in a row: params_snap = { 'input' : input, 'type' : 1, 'tool' : 1, 'threshold' : ...
131 views

### Using Google Encoded Polyline Algorithm Format with Oracle Database

Google's Encoded Polyline Algorithm Format is implemented in several GI tools. PostGIS e.g. has ST_AsEncodedPolyline and ST_LineFromEncodedPolyline functions. In contrast, Oracle Database has no ...
261 views

### How to get equidistant points from a linestring (geographical coordinates) [closed]

I want to resample geographical coordinates based on a specific number of values, let's say, 1663 for the following case: -78.0599088 -11.89402416 -78.04317744 -11.88622134 -78.0267798 -11.87700462 -...
260 views

### How to combine geometries and numbers in Google Earth Engine

Trying to combine coordinates (geometries) with their respective slope (numbers) in Earth Engine. I am quite lost as to how to go about doing this. I've tried using ee.Algoritm.Feature to add metadata ...
72 views

### Calculating closest distance from location to given route?

I want to calculate the closest distance from a location (lat/lon) to a given route. The route consists of approximately 20.000 location points. I could calculate the distance to every location point ...
89 views

### Seeking QGIS algorithm for Swapping land parcels/plots by property?

I've searched for a QGIS Algorithm for swapping plots in an area by land owners and I didn't find anything. Do you know something that did that? For example, in an area or in a town we have 2 big ...
243 views

### Listing multiple fields to be dropped at once in QGIS modeler?

I'm trying to drop more than one fields at once in QGIS 3 modeler on Microsoft Windows. I'm using the algorithm "Drop field(s)". What is the good syntax to list multiple fields to be dropped? Not ...
152 views

### Finding a boundary with a collection of lines and a point

Given a collection of lines and a point how can I discover the closest boundary around the point. In the image below A represents a collection of disconnected lines and B is the boundary I want to ...
94 views

### Scaling down lat/lon polygon?

I have a set of (lat,lon) coordinates that compose a polygon. Is there a straightforward method to get an analogous set of coordinates defining a smaller version of the polygon? For example, given ...
73 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 ...
57 views

### Seeking algorithms for DEM generation? [closed]

What are the different algorithms employed for the generation of a Digital elevation model from images captured using an unmanned aerial vehicle ?
743 views

### Can you auto-populate a field in Survey123 from another field by only pulling certain characters?

I have a field where the user inputs text Aa1Bb2Cc3 Am I able to auto populate another field by only populating the field with Bb or 3. Auto populate the field with characters [4:6] or just [9] ...