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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203 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
304 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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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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200 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
5k 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 ...
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23 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
51 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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0answers
22 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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114 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 ...
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1answer
51 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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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). ...
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1answer
293 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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35 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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72 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
362 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
439 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
409 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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35 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 ...
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1answer
117 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 ...
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2answers
854 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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263 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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0answers
125 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 ...
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137 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
164 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
335 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
208 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
2k 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
89 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
92 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
131 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
186 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
382 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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1answer
723 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 ...
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1answer
81 views

Seeking “path averaging” algorithms?

Imagine that I have collected a large set of GPS tracks of objects moving from A to B, and for the sake of simplicity assume they avoid obstacles in a consistent way, so that their path is just "noisy"...
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1answer
60 views

How to split lines that are larger than 10km?

I have a shapefile of line segments representing global rivers. The segments are all different lengths. If a segment is longer than 10km, I would like to divide it in to multiple segments approx 10km ...
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1answer
351 views

Split Up Big Polygon Into Smaller Ones By Condition

I have some big Polygon. Within it collection of leaflet layers (points). Every point have some numeric property. What I want is split up big Polygon into smaller ones. Every smaller polygon should ...
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1answer
131 views

How to find the direction of an “L” shape in a image

I need to find the moving direction of a vehicle by its extracted point cloud, and I have converted the point cloud to the following image. As the target vehicle could be moving straight or turning ...
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1answer
480 views

Error: Grid layer was not correctly generated

Faced this error already several times when I was playing with processing algorithms: I used hi-res DSM/DEMs out of UAV surveys. Resolution between 2,5 - 5 cm GSD. Output format: .tif Any ideas ...
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0answers
88 views

Seeking equation/algorithm for angle between straight line and grid north?

I have a cylindrical equidistant projection map containing climate data(equal angle and equal distances). On this projection I have a straight line connecting two latitude and longitude points. How ...
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1answer
3k views

Efficient route planning between a set of points and with a set of people

I have the following use case: A company needs to make winter service at a set of addresses in a city. To be as fast as possible covering all addresses an efficient route calculation is required. ...
3
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1answer
1k views

Finding longest line segment within polygon? [closed]

I have been looking around to find a way to calculate the longest line within a polygon. Determining longest line segment within polygon that passes through its centroid? and Calculating maximum ...
4
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1answer
524 views

Determine whether a 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 lng for all points) fails on ...
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0answers
49 views

Choose between 2 algorithms in my script

I would like to know how can user chooses between 2 algorithm's parts in my script. User must be able to chose between 2 methods to integrate a variable : automatically with a character selection in ...
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0answers
121 views

How to calculate if a turn is required from a set of coordinates?

I have some polyline data that represents a navigation route generated using Dijkstra's algorithm. Along this route I would like to calculate anytime a turn is required. Ideally, this would be some ...
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1answer
3k views

Finding nearest neighbors of each coordinate

I've got a list of coordinates (WGS1984 Decimal Degree) and have started work on a program that performs a DBSCAN on them to find clusters amongst them. To perform the DBSCAN's range query to ...
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1answer
373 views

GRASS algorithms not working in QGIS 2.18.5

I've installed QGIS Las Palmas and still trying to learn its capabilities. There is however problem with GRASS algorithms grouped in the geoprocessing tools. Some of them work (item 2) and others don'...
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1answer
111 views

Seeking algorithm to find point on surface with highest visibility?

I have a DEM which I want to find a point with largest amount of visibility ,I know that viewshed leads to visibility from a point but how can I find a point with highest visibility ? One way is to ...
13
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1answer
557 views

Detecting branched polygon shape?

I have a vector layer with millions of polygons making continuous coverage. I need to classify them according to their shape. I am already using several shape indexes from landscape ecology like ...
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1answer
119 views

How to determine relative position of a new waypoint in an array of waypoints?

I hope this is not a ridiculously stupid question but I can't seem to come up with an immediate algorithm for this: I have a list of (lat,lng), which represent a list of waypoints on a map. At any ...
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0answers
415 views

How to calculate a weighted center of a set of zip codes [duplicate]

I have the zip codes for the US and their population. I need to calculate the weighted center. I have tried finding the zip code with the minimum sum(distance_to_zip * zip_population) This works ...