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Questions tagged [concave-hull]

Smallest bounding geometry of an object or group of objects using concave angles. Also known as an alpha hull or shape.

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ST_ConcaveHull recomposes polygon without much regard to concavity?

What am I missing in understanding this behavior of concave hull? My primitive understanding is that it applies a "shrink wrap" algorithm. But consider this example where I decompose a polygon into ...
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1answer
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Concave hull error: not enough arguments

I am trying to run concave hull on a points layer, but I keep running into this error: TypeError: translate(str, str, disambiguation: str = None, n: int = -1): not enough arguments What am I doing ...
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Creating polygon data envelope using QGIS? [duplicate]

I've got data points (xyz data) of which I need an envelope in the form of a shapefile or polyline. I realize that there has to be done some form of interpolation. A method that approximately ...
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1answer
2k views

Creating concave hull with Python?

I'm trying to follow this tutoriel to do a concave hull script : Drawing Boundaries In Python Of course, I drop all steps for plot results. But at the and of my script I have an error. This is last ...
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Alpha hull with island

I need the 'concave hull' or alphashape of a set of points. Also, I'd like to have it with holes/donuts/islands in the middle. See my attached image. The outer hull is being calculated fine. But the ...
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240 views

Looking for a US state file for geofences with as few geofences per state as possible (so group islands with mainland)

UPDATED TO MUCH MORE DETAILED QUESTION I'm building a set of geofences to be installed on a GPS unit to track vehicles as they cross state lines. The list of geofences are simple latitude/longitude ...
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1answer
173 views

ST_ConcaveHull produces “No function matches given name” in PostGIS?

I'm using Postgis 2.2.2. This is my table: county | character varying | wkb_geometry | geometry(Polygon,27700) | I want to get the area of the concave hull around all polygons in a ...
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Creating bounding extent of existing polygon with same geometry using QGIS? [duplicate]

I have a number of polygons (in the hundreds) that have been taken from a cadastral layer and I am trying to create another polygon layer based on that group of polygons (from a field ID) without ...
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1answer
159 views

How do I draw the shortest imaginary boundary around a point dataset?

I would like to produce a range map for my species (smooth snakes in the south of England) using the IUCN-defined 'extent of occurrence' (EOO) as my metric. EOO is defined as 'the area contained ...
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1answer
246 views

Split a polygon based on point groups (QGIS)

I have a project with two layers: A work area as a single polygon A set of points all contained in the previous area I would like to divide the original area into 5 polygons/features that all ...
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Adapting a ConvexHull fonction to a ConcaveHull one

I have a database with over 150 000 points in a EPSG 2950 projection. As I wanted to cluster those points in polygons, I used a ConvexHull fonction. The goal was to create clusters where I would find ...
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Wrap the set of points to the minimum polygon

Given I have a set of points which represents the circles which are intersected. As result I'm trying to receive the boundary which represent the polygon which wraps all circles. Please take a look ...
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1answer
267 views

Packing polygons without intersection and empty places [closed]

How can I pack polygons without empty places and intersections? Please tell me everything that might help me (API, algorithms, etc.) I'm using: USPS API to get carrier routes. dbscan.js to ...
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1answer
303 views

Convert fields of points into separate polygons based on their outlines

I have several fields of points that look like so: They are actually thousands of points that appear as polygons because they're so close to one another. They're research points 720 feet from one ...
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2answers
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Drawing outline of point cloud using QGIS?

I want to know if there is a plugin in QGIS, which will allow me to draw the outline a point cloud. I know there Points2One the plugin, but it makes an outline with all points, even with the data ...
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1answer
273 views

Bounding geometry convex hull

I have huge point clouds (Millions of points): I need to create a shapefile with the boundary of this point cloud. When I was working with this 2 months ago I could do this somehow: I'm pretty sure ...
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1answer
2k views

Looking for an alternative to Minimum Bounding Geometry (convex hull) tool for creating polygons from points

I have lines of points that I'd like to connect to create individual polygons. The Minimum Bounding Geometry tool is great because it lets me input many points at once and use the "Group" option to ...
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0answers
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How to create concave polygon with constraint angles in qgis?

I'm having point data. By using that I wanna create concave polygon with some constraint angles (i.e., >45 and <225 degree). Is it possible to do in QGIS?
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How to remove temporary layer source files in QGIS

I am new to QGIS and python. Titles says it all. I'm modifying a plugin that creates some temporary files (layers) during it's run and I need to loop it a couple times. The algorithm works fine for ...
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0answers
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Extract the outer points of a Point Shape into a Line Shape? [duplicate]

I've installed QGIS 2.8.2 since a few days and have no experience with this application. I try to extract the outer points of a Point Shape into a Line Shape, like a shell for the inner points. All ...
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2answers
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C# implementation of concave hull / alpha shapes

I'm looking for a C# implementation of the Concave hull (alpha shapes) algorithm. I already found several Java, Python and C++ implementation but no C# version. The other implementation are quite ...
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1answer
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Create Complex Polygon from Point Layer using only Boundary Points in ArcGIS

I need to convert a point layer to a polygon, using the boundary points from a complex grid to define the polygon's edges. This has been addressed as questions for other formats (postGIS, QGIS), but ...
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2answers
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How to find the concave hull for a cloud of points in 3D space?

The existing algorithm for convex hull is not able to capture the feature for a set of 3D points. Moreover, I found few mathematic tools have this function to obtain the concave hull and their ...
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1answer
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Convex Hull operation not specific enough

I have yield data as point values, and I simply want to create the boundary around this layer. I have used the Minimum Bounding Geometry tool and selected Convex Hull to do this, however it maintains ...
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How to create polygon made from outside points of points shp? [duplicate]

I have DEM Data which is in SHP Format. After interpolating to raster, I need to clip the raster image. To do this, I need to transform the Point SHP into a Polygon SHP using only the outer-most ...
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1answer
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QGIS equivalent to ArcGIS Aggregate Polygons?

I am looking for a tool in QGIS 2.40 that performs the function ArcGIS refers to as Aggregate Polygons. Basically it takes a group of polygons within a specified distance and creates a concave hull ...
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1answer
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Creating polygon from exterior points using PostGIS?

How to convert points data to polygon, so as to form polygon from exterior point as shown above
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1answer
911 views

How to grow several concave hulls until they completely fill a larger area without overlap?

This is my problem: I have a very large point layer with polling station locations across one country; each point belongs to a specific constituency (900k points, 4k constituencies). I wish to use ...
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2answers
773 views

animate polygons in series of kml/geojson/shp

I have a series of KML files (though they could easily be converted to geoJSON, SHP, or anything else that ogr2ogr can handle), each file containing a set of polygons that correspond to the alpha ...
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1answer
2k views

Map projection lat, lon to pixel?

I'm trying to find the concave hull of a lat, lon pointset but when I project my points on my map it doesn't look like expected. I've tried a lineare projection and a spherical projection. My data is ...
6
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1answer
465 views

Hitting Memory Limits of PostGIS ST_ConcaveHull / Incomplete Shrink Wrap

I am trying to use PostGIS 2.0 on Postgres 8.4 to do some mapping. I am working with the NOAA Shapefiles, specifically their US States & Territories file located here: http://www.nws.noaa.gov/...
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2answers
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Is it possible to get the points used for the convex hull in osm2po?

I have a non-convex hull algorithm that I want to use for an app. With OSM2PO, it's possible to get a convexHull, but is there a way to get the points before the hull is constructed? More, it would ...
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How can I use Convex Hull to select an area with a space from the points?

This refer to this post : Read Here My goal is to select an area covering some points, but maintaining some space from points of border, like in the follow picture : I think ST_Convexhull will do ...
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Algorithm to find polygons enclosing points

I'm trying to find an algorithm that can determine the smallest possible polygons to cover a number of points. I know how to get the convex hull around all the points, but say that the points are ...
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13answers
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What are Definition, Algorithms and Practical Solutions for Concave Hull? [closed]

Convex Hull A convex hull of a shape is defined as: In mathematics, the convex hull or convex envelope for a set of points X in a real vector space V is the minimal convex set containing X (...