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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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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 ...
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2answers
31 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 ...
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1answer
30 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 ...
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1answer
17 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 ...
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0answers
44 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 ...
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39 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 ?
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30 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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30 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 ...
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1answer
70 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 ...
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95 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 ...
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0answers
60 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 ...
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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 ...
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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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76 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....
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1answer
51 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 ...
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1answer
113 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
43 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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41 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/...
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2answers
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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 ...
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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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41 views

Error message with the v.to.3d algorithm on MacOS Sierra 10.12.6

I am very new to QGIS and Im having trouble running the v.to.3d algorithm as I get the error message below. Traceback (most recent call last): File /Applications/QGIS3.app/Contents/MacOS/../Resources/...
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0answers
19 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 ...
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1answer
43 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 ...
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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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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 ...
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1answer
37 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 ...
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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). ...
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1answer
76 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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18 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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45 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
70 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. ...
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1answer
191 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(...
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1answer
203 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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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 ...
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1answer
58 views

Pipe custom processing algorithm output into another in QGIS 3.0

Following up on this question, I am writing a Processing python script based on the template provided here. It takes a few additional parameters in addition to the 'INPUT' and 'OUTPUT' from the ...
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1answer
397 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 '...
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211 views

how do I enter start point in shortest path algorithm in QGIS 3.0.1?

Are the x and y values displayed by the Vertex Editor (bottom left of image) not the same as the x and y values in my TestNetwork layer required by the Shortest path algorithm?
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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 ...
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0answers
61 views

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- ...
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1answer
104 views

Setting GroundFilter parameters for low density point clouds?

I'd like to use the function GroundFilter on my dataset. However, the manual says that the default values of the parameters used by this function (g parameter, w parameter) are related to a high ...
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1answer
249 views

Given a lat/long find all points within a certain radius

I am looking to find multiple lat/long points (N,S,E,W) that are 100 metres from an input lat/lon point I have stored in PostGIS. So, given a latitude and longitude I'd like to find the latitude and ...
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1answer
182 views

Create points at specified distance from each other in random fishnet's cells while being on linestrings

We have a land protocol where we receive a fishnet of 1x1 km cells. Some cells are randomly choosed. We need to put 4 points in each cell and these points have to be on a road too. The minimum ...
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3answers
504 views

Converting Coordinate systems [closed]

I have coordinates in *GPS (WGS84) (deg) format and I need convert them to South African Cape/Lo27 format. I know I can do this on this website (https://twcc.fr/en/#), but unfortunately I need to ...
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1answer
65 views

Select n cells from a raster maximizing their variance

I work in R, especially using 'raster' package. It is a computational problem too hard for my syntax capacities. STEP 1. I have a one band raster, and what I want to select is a set of n cells (in my ...
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0answers
70 views

How to clip an enormous shapefile [closed]

The images below is a snippet of 2 shapefiles. 1) every building in the UK (13,971,598 features) 2) blue polygons The goal is to clip or select all the buildings that fall within the blue polygon ...
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0answers
78 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%....
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1answer
117 views

How to incrementally add points to a polygon and eventually increasing the size of the polygon in postgis?

I want to implement a clustering algorithm in postgis in which new points are incrementally added to an existent polygon and the polygon subsequently increases it's size to a the minimum possible ...
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0answers
156 views

Standard Method to calculate Average Moving Speed from Times & Coords?

...I wasn't sure if this question was best suited to GIS, SO or Math, so after reading GIS Topics I decided to ask here, but I'll relocate if necessary... :-) I'm working on automating various ...
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0answers
44 views

Store created vectors into a new line layer

I have two separate point layers and I want to connect the points of both layers based on a comparison of a specific attribut (for further information of my situation, please visit this question where ...
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1answer
397 views

Creating line between two points with same value using QGIS?

I have two separate point layers. The first point layer contains the locations of 100 sensors which are aligned in one specific direction (for example: Asten). The second point layer contains the ...