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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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1answer
58 views
+50

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 ...
0
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1answer
24 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. ...
2
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1answer
33 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 ...
0
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1answer
42 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: { ...
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2answers
333 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 ...
3
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0answers
39 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 ...
1
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1answer
72 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 ...
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0answers
30 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 ...
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1answer
84 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, ...
1
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1answer
79 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, ...
2
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1answer
61 views

PyQGIS Processing: “memory: not found”

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' : ...
0
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1answer
45 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 ...
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1answer
53 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 -...
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1answer
37 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 ...
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0answers
37 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 ...
0
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1answer
72 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 ...
1
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2answers
70 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 ...
1
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1answer
57 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 ...
0
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1answer
26 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 ...
2
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0answers
52 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 ...
4
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1answer
46 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 ?
2
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1answer
153 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] ...
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1answer
52 views

Find QGIS algorithm path

According to Using QGIS3 Processing algorithms from standalone PyQGIS scripts (outside of GUI) I try to implement the existing "Split Lines with Lines" algorithm into a QGIS Plugin. To do this I need ...
1
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1answer
80 views

What algorithm was used for generation of this vector layer?

The second image is a raster layer and in the third image obtained vector layer is so accurate. What algorithm would have been employed? Normal methods doesn't give nearly equal vectorization. I ...
7
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1answer
126 views

Optimal tiling of polygon using ArcGIS Desktop?

I am trying to tile a polygon with a minimal number of fixed sized squares. Currently I am creating a fishnet over my polygon then spatially joining the squares that intersect the polygon. This is ...
2
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0answers
74 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 ...
3
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2answers
57 views

Can Ksp Algorithm(Shortest Path Algorithm) have a constraint that the suggested paths must include a particular node or link

I am using pgr_ksp algorithm to find out the shortest path between a startnode and endnode by creating a network topology between all the nodes. Pgr_ksp algorithm very well gives me all the shortest ...
2
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1answer
116 views

Algorithm “qgis:difference” doesn't work in pyQGIS 3

I try to use native algorithm difference of QGIS. But it seams it doesn't work like the others : parameters = {'INPUT': polygons['OUTPUT'], #from temporary layer created before 'OVERLAY'...
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0answers
133 views

Debugging Error: Algorithm gdal:dissolve not found in PyQGIS?

I have difficulties with the processing package. I try to run a simple QGIS dissolve in pyQGIS 3. When I run the line : from qgis.core import QgsVectorLayer import processing from processing.core....
0
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2answers
114 views

Is the Random Trees Classifier in ArcMap 10.5 equal to Random Forest?

Is the Random Trees Classifier in ArcMap 10.5 the same as what is named Random Forest in other applications/software? I see that the parameters are the same and the design seems the same, but I need a ...
1
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1answer
184 views

Error: Algorithm not found with correct processing use

I try to run a simple dissolve algorithm in a standalone Python 3 script. My code is following : from qgis.core import QgsVectorLayer import processing from processing.core.Processing import ...
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0answers
60 views

Algorithm or library for buffer zone for lat-lon (wgs) coordinates in global scale

Can anyone point to generic algorithm or library for buffer zones if the source data is in WGS84 degrees? The buffer width should be in meters, as buffer in degrees it generally does not make much ...
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0answers
106 views

Formula to calculate DGPS correction factors

I am trying to implement a differential GPS algorithm. During my research, I found a paper at https://opus.bibliothek.uni-wuerzburg.de/opus4-wuerzburg/frontdoor/deliver/index/docId/11361/file/...
3
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2answers
2k views

Creating buffer circle x kilometers from point using Python?

I am wanting to create a circle with an inputted radius around a point of predetermined latitude and longitude. I've been trying to use the formula found in this post which uses an algorithm ...
0
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0answers
37 views

Determining average local azimuth of stream channel?

I am working with some LiDAR based DEMs to examine stream channel and riparian morphology. I want to determine, given a point in a stream, the average azimuth that the stream is heading within a ...
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0answers
20 views

Dividing space into homogeneous connected areas [duplicate]

Is there an algorithm (or software) for splitting a map into K connected areas such that the within-area variance of some variable is minimised, and the between-area variance of that variable is ...
1
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1answer
46 views

Remove small interstices on the edges of a polygone

How can I remove the white interstices on the edges (and interior) of a polygone or polyline, as represented in the first figure below? I want to get smooth and continuous edges, capturing the global ...
2
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0answers
19 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. ...
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0answers
92 views

Speed 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 extract ...
1
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1answer
40 views

Problem with number entry QGIS modeler

i created some number entry in QGIS modeler I created them specifically for them to be decimal numbers and not integer. But when i try my model, when i put a decimal number like 0.255 the value ...
3
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0answers
33 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). ...
1
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1answer
128 views

How to link Number value with Field calculator in QGIS Modeler ?

I want to link 2 number values (RMSE & dosemax) in a field calculator formula. When I run the modeler, I add these values but it doesn't recognize them. I dont want to create a new table. Just use ...
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0answers
23 views

Understanding the problem of applying A* on a multilevel network

I am currently working on an indoor routing project for a multilevel building.For this, I want to find a shortest path over multiple level (or 'floors'). I have read some papers on A* in such an ...
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0answers
58 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 ...
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0answers
202 views

Convert Raster to grid [duplicate]

I want to convert or a raster into a grid. I am with QGIS. I have a raster of a parcel. I have a vector grid of the same area. I want to add in each block of the grid a mean value of the raster. ...
2
votes
1answer
286 views

How to memorize temporary layer from processing.runalg() in pyqgis?

I created some geoalgorithms with QGis and I need to use them in a Python script. By saving the layer obtained in a file having a specific path, I do not have problems. For example: processing.runalg(...
2
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1answer
281 views

Let QGIS 3.0 Processing algorithm output a VectorLayer loaded via the delimited text provider

Following up on this question, I need to be able to setup the QgsVectorLayer loaded via the delimitedtext provider as my algorithm output. Note that I am still working from this template. For lack ...
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0answers
33 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 ...
3
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1answer
86 views

Piping custom processing algorithm output into another in QGIS?

I am using QGIS 3.0. Following up on Calling a QgsProcessingAlgorithm from a Processing python script in QGIS 3.0?, I am writing a Processing python script based on the template provided here. It ...
2
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1answer
552 views

Calling a QgsProcessingAlgorithm from a Processing python script in QGIS 3.0?

I am writing a Processing python script based on the template provided here. I am creating lines (destined to the 'OUTPUT') and I would like to clip them according to a polygon entered as the '...