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Finding algorithms of QGIS commands?

What are Definition, Algorithms and Practical Solutions for Concave Hull?Finding center of geometry of object?Finding minimum-area-rectangle for given points?Learning resources for beginning differential topology for a programmer?How to Create a Minimum Bounding Polygon in QGISWhat algorithm does QGIS use to calculate Nearest Neighbor Index?Calculate area of geometry derived from current feature in QGIS 2.8Finding documentation for arcpy.gp functions?Creating Minimum Convex Polygon - Home Range from Points in QGISHow to generalize shape with PyQGIS without much Distortion in the shape?

5

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 polygon

Does anyone knows where I can find them?

qgis algorithm documentation

share|improve this question

edited Mar 12 at 10:57

Vince

14.7k32749

asked Mar 12 at 10:04

Koen VenkenKoen Venken

554

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  docs.qgis.org/testing/en/docs/user_manual/processing/…
  
  – Fran Raga
  Mar 12 at 10:31
  

  
  
  
  


• 
  
  
  

  
  5
  

  
  
  
  
  
  

  
  
  It's open source software. As the the old spaghetti sauce commercial used to say, "It's in there."
  
  – Vince
  Mar 12 at 11:01
  

  
  
  
  

add a comment | 

5

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 polygon

Does anyone knows where I can find them?

qgis algorithm documentation

share|improve this question

edited Mar 12 at 10:57

Vince

14.7k32749

asked Mar 12 at 10:04

Koen VenkenKoen Venken

554

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  docs.qgis.org/testing/en/docs/user_manual/processing/…
  
  – Fran Raga
  Mar 12 at 10:31
  

  
  
  
  


• 
  
  
  

  
  5
  

  
  
  
  
  
  

  
  
  It's open source software. As the the old spaghetti sauce commercial used to say, "It's in there."
  
  – Vince
  Mar 12 at 11:01
  

  
  
  
  

add a comment | 

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 polygon

Does anyone knows where I can find them?

qgis algorithm documentation

share|improve this question

edited Mar 12 at 10:57

Vince

14.7k32749

asked Mar 12 at 10:04

Koen VenkenKoen Venken

554

share|improve this question

edited Mar 12 at 10:57

Vince

14.7k32749

asked Mar 12 at 10:04

Koen VenkenKoen Venken

554

share|improve this question

edited Mar 12 at 10:57

Vince

14.7k32749

asked Mar 12 at 10:04

Koen VenkenKoen Venken

554

edited Mar 12 at 10:57

Vince

14.7k32749

edited Mar 12 at 10:57

Vince

14.7k32749

asked Mar 12 at 10:04

Koen VenkenKoen Venken

554

asked Mar 12 at 10:04

Koen VenkenKoen Venken

554

2 Answers
2

active

oldest

votes

14

The "minimum bounding geometry" and "clip polygon" algorithms in QGIS are implemented in /python/plugins/processing/algs/qgis/MinimumBoundingGeometry.py and /src/analysis/processing/qgsalgorithmclip.cpp.

If you follow through the source of these, you'll find that they rely on geometry-related functions from a C++ class called QgsGeometry, specifically QgsGeometry::convexHull() and QgsGeometry::intersection(). The "clip" algorithm also contains additional logic for building a union of geometries to form a mask polygon, as well as testing for points within the polygon, in the case of non-polygon vectors.

Reading through the QgsGeometry class shows that the actual algorithms themselves are implemented in a library called GEOS. GEOS is a C++ port of a Java library called the JTS Topology Suite, which implements a suite of geometry-related algorithms.

The core of the ConvexHull algorithm from GEOS is implemented here using an algorithm called Graham's scan. The implementation of intersection in GEOS is a bit more complicated and spread out, but here's a place to start looking. GEOS supports various binary operations between geometries and "intersection" is only one of them.

In general, GEOS is the place to look for the implementations of the various vector algorithms in QGIS, but there are also some raster algorithms in QGIS which are implemented by the GDAL library.

share|improve this answer

answered Mar 12 at 12:16

Candy GumdropCandy Gumdrop

36114

add a comment | 

6

You can check the algorithms at QGIS Github and find scripts for all the tools such as the minimum bounding geometry.

share|improve this answer

answered Mar 12 at 10:13

JosephJoseph

58k7100201

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  While these links are good starting points, it's worth noting that the algorithms themselves aren't in the QGIS source repository.
  
  – Candy Gumdrop
  Mar 12 at 13:24
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @CandyGumdrop - Thanks for providing a comprehensive answer :)
  
  – Joseph
  Mar 13 at 10:14
  

  
  
  
  

add a comment | 

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14

The "minimum bounding geometry" and "clip polygon" algorithms in QGIS are implemented in /python/plugins/processing/algs/qgis/MinimumBoundingGeometry.py and /src/analysis/processing/qgsalgorithmclip.cpp.

If you follow through the source of these, you'll find that they rely on geometry-related functions from a C++ class called QgsGeometry, specifically QgsGeometry::convexHull() and QgsGeometry::intersection(). The "clip" algorithm also contains additional logic for building a union of geometries to form a mask polygon, as well as testing for points within the polygon, in the case of non-polygon vectors.

Reading through the QgsGeometry class shows that the actual algorithms themselves are implemented in a library called GEOS. GEOS is a C++ port of a Java library called the JTS Topology Suite, which implements a suite of geometry-related algorithms.

The core of the ConvexHull algorithm from GEOS is implemented here using an algorithm called Graham's scan. The implementation of intersection in GEOS is a bit more complicated and spread out, but here's a place to start looking. GEOS supports various binary operations between geometries and "intersection" is only one of them.

In general, GEOS is the place to look for the implementations of the various vector algorithms in QGIS, but there are also some raster algorithms in QGIS which are implemented by the GDAL library.

share|improve this answer

answered Mar 12 at 12:16

Candy GumdropCandy Gumdrop

36114

add a comment | 

14

The "minimum bounding geometry" and "clip polygon" algorithms in QGIS are implemented in /python/plugins/processing/algs/qgis/MinimumBoundingGeometry.py and /src/analysis/processing/qgsalgorithmclip.cpp.

If you follow through the source of these, you'll find that they rely on geometry-related functions from a C++ class called QgsGeometry, specifically QgsGeometry::convexHull() and QgsGeometry::intersection(). The "clip" algorithm also contains additional logic for building a union of geometries to form a mask polygon, as well as testing for points within the polygon, in the case of non-polygon vectors.

Reading through the QgsGeometry class shows that the actual algorithms themselves are implemented in a library called GEOS. GEOS is a C++ port of a Java library called the JTS Topology Suite, which implements a suite of geometry-related algorithms.

The core of the ConvexHull algorithm from GEOS is implemented here using an algorithm called Graham's scan. The implementation of intersection in GEOS is a bit more complicated and spread out, but here's a place to start looking. GEOS supports various binary operations between geometries and "intersection" is only one of them.

In general, GEOS is the place to look for the implementations of the various vector algorithms in QGIS, but there are also some raster algorithms in QGIS which are implemented by the GDAL library.

share|improve this answer

answered Mar 12 at 12:16

Candy GumdropCandy Gumdrop

36114

add a comment | 

The "minimum bounding geometry" and "clip polygon" algorithms in QGIS are implemented in /python/plugins/processing/algs/qgis/MinimumBoundingGeometry.py and /src/analysis/processing/qgsalgorithmclip.cpp.

If you follow through the source of these, you'll find that they rely on geometry-related functions from a C++ class called QgsGeometry, specifically QgsGeometry::convexHull() and QgsGeometry::intersection(). The "clip" algorithm also contains additional logic for building a union of geometries to form a mask polygon, as well as testing for points within the polygon, in the case of non-polygon vectors.

Reading through the QgsGeometry class shows that the actual algorithms themselves are implemented in a library called GEOS. GEOS is a C++ port of a Java library called the JTS Topology Suite, which implements a suite of geometry-related algorithms.

The core of the ConvexHull algorithm from GEOS is implemented here using an algorithm called Graham's scan. The implementation of intersection in GEOS is a bit more complicated and spread out, but here's a place to start looking. GEOS supports various binary operations between geometries and "intersection" is only one of them.

In general, GEOS is the place to look for the implementations of the various vector algorithms in QGIS, but there are also some raster algorithms in QGIS which are implemented by the GDAL library.

share|improve this answer

answered Mar 12 at 12:16

Candy GumdropCandy Gumdrop

36114

share|improve this answer

answered Mar 12 at 12:16

Candy GumdropCandy Gumdrop

36114

answered Mar 12 at 12:16

Candy GumdropCandy Gumdrop

36114

answered Mar 12 at 12:16

Candy GumdropCandy Gumdrop

36114

6

You can check the algorithms at QGIS Github and find scripts for all the tools such as the minimum bounding geometry.

share|improve this answer

answered Mar 12 at 10:13

JosephJoseph

58k7100201

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  While these links are good starting points, it's worth noting that the algorithms themselves aren't in the QGIS source repository.
  
  – Candy Gumdrop
  Mar 12 at 13:24
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @CandyGumdrop - Thanks for providing a comprehensive answer :)
  
  – Joseph
  Mar 13 at 10:14
  

  
  
  
  

add a comment | 

6

You can check the algorithms at QGIS Github and find scripts for all the tools such as the minimum bounding geometry.

share|improve this answer

answered Mar 12 at 10:13

JosephJoseph

58k7100201

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  While these links are good starting points, it's worth noting that the algorithms themselves aren't in the QGIS source repository.
  
  – Candy Gumdrop
  Mar 12 at 13:24
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @CandyGumdrop - Thanks for providing a comprehensive answer :)
  
  – Joseph
  Mar 13 at 10:14
  

  
  
  
  

add a comment | 

You can check the algorithms at QGIS Github and find scripts for all the tools such as the minimum bounding geometry.

share|improve this answer

answered Mar 12 at 10:13

JosephJoseph

58k7100201

share|improve this answer

answered Mar 12 at 10:13

JosephJoseph

58k7100201

answered Mar 12 at 10:13

JosephJoseph

58k7100201

answered Mar 12 at 10:13

JosephJoseph

58k7100201