Questions tagged [geometry]
(1) abstract geometry; (2) storing geographic data in projected coordinates; (3) a generic ESRI term for vector features; a class for "geometry" objects.
1,884
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What are Definition, Algorithms and Practical Solutions for Concave Hull?
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 (Wikipedia)...
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votes
4
answers
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Getting coordinates from geometry in PostGIS
This line:
SELECT geom
FROM myLayer.geom
will return a hex value.
How would I get decimal values, which is a human-readable coordination?
- 1,299
97
votes
8
answers
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Finding minimum-area-rectangle for given points?
As you see in the figure, the question is:
How to find the minimum-area-rectangle (MAR) fitted on the given points?
and a supporting question is:
Is there any analytical solution for the ...
- 3,407
88
votes
6
answers
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Visualising WKT geometry string in QGIS
Is there a simple tool in QGIS to graphically visualise geometry formatted as text?
Example geometry:
POLYGON((571178 6337246,571178 6402217,598061 6402217,598061 6337246,571178 6337246))
Result:
A ...
- 4,500
60
votes
11
answers
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Removing small spaces (slivers) between polygons
I have a set of polygons representing administrative districts. The districts were digitized by hand, and there are small spaces (slivers) between polygons where the polygons should be touching.
How ...
- 711
50
votes
5
answers
96k
views
Smoothing/generalizing polygon in QGIS
Is it possible to smooth or generalize a polygon in QGIS, perhaps by using a plugin like the Generalizer Plugin for lines?
I could convert my polygons to lines, smooth them and convert them back to ...
- 8,358
47
votes
10
answers
111k
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Determining the centroid of polygons in QGIS
I have a polygon vector and I want to quickly attain the centroid of this polygon for insertion in a text document. I am working with QGIS. I searched through other questions and although some are ...
- 771
43
votes
1
answer
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Finding center of geometry of object?
Given a set of 2D or 3D points:
How to find the center of geometry of an object?
According to the following figure, the center of geometry differs from the center of mass if it is calculated in the ...
- 3,407
37
votes
7
answers
46k
views
Fixing geometry validity errors in QGIS 2
I am working on ownership data at a US county level. I have one shapefile per county that contains thousands of tax parcels. I need to dissolve the polygons representing parcels owned by the same ...
- 983
34
votes
2
answers
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How is ST_PointOnSurface calculated?
The PostGIS documentation states that ST_PointOnSurface returns "a POINT guaranteed to lie on the surface". It seems like this function could be trivially implemented to give results that satisfy the ...
- 443
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votes
1
answer
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Storing GeoJSON FeatureCollection to PostgreSQL with PostGIS?
I am new to GeoJSON. I have a GeoJSON features collection as shown and would like to store it in postgres table (testtable). My postgres table has a serial id and geometry column.
{
"type": "...
- 333
32
votes
4
answers
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Filter by bounding box in GeoPandas
I have a GeoPandas DataFrame in EPSG:4326 and I'd make a new DataFrame consisting of all the rows that fall within a certain bounding box.
First I get the bounding box that I care about (which is ...
- 3,319
32
votes
3
answers
58k
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Copy a geometry from one feature to another without attributes?
With QGIS it's easy to add a new part to an existing feature/geometry but I can't see how to copy/paste this part from another existing feature/geometry.
Is it possible?
- 515
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votes
4
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Create a geography/geometry column from x and y fields - SQL Server 2008
I'm new in SQL Server 2008 and I hope you will understand my question/need.
Thus, I have a table which contains 3 fields (Name, Lat and Long) in my data base (spatial). I want to create a geometry/...
- 331
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4
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How to find the maximum-area-rectangle inside a convex polygon?
In this post we are looking for algorithms / ideas on how to find the maximum-area-rectangle inside a convex polygon.
In the following figure, numbers are the areas of the fitted rectangles. As shown ...
- 3,407
29
votes
3
answers
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Converting GeoJSON to Python objects? [closed]
New to the site, and to geoJSON, and to python.
My goal is to read in a file with geoJSON data, and use it to generate shapes to be used in an application that is using python scripting. Python ...
- 393
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votes
7
answers
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Filling holes in polygons using QGIS
Is there an option in QGIS to fill holes in polygons automatically by setting parameters e.g. maximum area, distance between borderlines?
I want to delete/fill holes that a very "thin"/small....
- 259
24
votes
3
answers
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How to store lines and polygons in JSON documents?
Looking at the increasing NoSQL movement and considering that databases like MongoDB offers a new perspective in flexible data storage for GIS. What is the best way to store lines and polygons in ...
- 9,845
24
votes
3
answers
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Seeking Generalisation Strategies for Building Outlines in PostGIS?
I have a dataset of building footprints vectorised from a raster dataset. The dataset is currently just a vector representation of the raster data. I would like a polygon dataset that only has ...
- 6,127
24
votes
2
answers
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How can I find a point inside a polygon in PostGIS?
How can I find a point that is guaranteed to be within a given polygon in PostGIS?
I am aware of the ST_Centroid function. However, the centroid is not always within a polygon, see below:
...
- 9,381
23
votes
6
answers
82k
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Converting shapefile to CSV including attributes and geometry
I have a shapefile with 60k+ entries, all of which are polygons with corresponding attributes (acreage totals, landowner names, tax ID #s, etc.). What I ultimately need is a CSV file with all of ...
- 231
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votes
3
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How to calculate the angle at which two lines intersect in PostGIS?
I want to calculate the angle between two lines where they intersect in PostGIS.
The starting point for angle calculations in PostGIS seems to be ST_Azimuth - but that takes points as input. My first ...
- 1,680
23
votes
1
answer
1k
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Space filling between random 2D lines
Consider a region (2D) filled with lines randomly (following Figure). We are interested in filling the empty spaces between lines including four boundary edges in a way:
0- maximizing the size of ...
- 3,407
21
votes
2
answers
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How to draw polygons from the python console?
I've been visiting and revisiting the page on geometry handling in the PyQGIS Cookbook: http://documentation.qgis.org/2.0/en/docs/pyqgis_developer_cookbook/geometry.html but can't seem to figure out ...
- 2,125
20
votes
1
answer
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Postgis - Converting 'geometry_dump' data type to a 'geometry' type
I am working with a dataset of property boundaries that has had ST_Union() run on it, thus all the polygons appear as a multi polygon in one row of a table. I would like to separate these out so I get ...
- 403
19
votes
5
answers
8k
views
Comparing two geometries in ArcPy?
I am trying to compare two separate feature classes to identify differences between them (sort of a diff function). My basic workflow:
I extract the geometries using a SearchCursor
Save the ...
- 794
19
votes
3
answers
4k
views
What is the precision of SELECT DISTINCT on PostGIS geometry column?
I wonder what the precision of the SELECT DISTINCT operator is on a PostGIS geometry. On my system, the following query gives me a count of 5, which means that the inserted points are considered equal ...
- 3,033
19
votes
2
answers
10k
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Finding tunnel center line?
I have some map files consisting of 'polylines' (each line is just a list of vertices) representing tunnels, and I want to try and find the tunnel 'center line' (shown, roughly, in red below).
I've ...
- 291
18
votes
2
answers
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Difference between QgsPoint, QgsPointXY and QgsGeometry.fromPointXY() in PyQGIS
I am using PyQGIS. What is the difference between:
QgsGeometry.fromPointXY(QgsPointXY(x, y))
QgsPointXY(x, y)
QgsPoint(x, y)
When I print these three options, I get:
print(QgsGeometry.fromPointXY(...
17
votes
3
answers
60k
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How I get SRID from Geometry field
What is the function for getting SRID from Geometry field.
I have inserted a shapefile into SQL Server table with a Geometry field defined. I know the projection of shapefile is Swreff99_1800 (EPSG:...
- 1,427
17
votes
3
answers
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Inverting Polygons using QGIS?
I have a Shapefile with Polygon features representing the world's land areas (continents, islands).
Is it possible to invert these, and get a geometry that represents the world's oceans and seas?
...
- 802
17
votes
6
answers
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Deleting duplicate geometry in PostGIS tables
After - I don't know what happened - all my entries in my PostGIS tables are doubled. I tried this to delete them but it does not delete any/all duplicates:
DELETE FROM planet_osm_point
WHERE ...
- 8,358
17
votes
6
answers
14k
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Converting between Esri Geometry and WKT using ArcObjects?
It seems like there is no means of converting an ArcObjects geometry to the Well-Known Text representation (and vice versa) in ArcGIS ArcObjects API. The only thing I was able to find is conversion to ...
- 10.3k
17
votes
3
answers
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Removing duplicate features with same geometry in ArcMap?
Is it possible to uniquely identify each geometry in a feature layer?
Essentially I have a polygon feature layer with many rows of data represented by the same geometry. I would like 1 row for each ...
- 520
17
votes
2
answers
11k
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Correcting gaps and overlapping polygon (parcels) geometry
I have come across a resource that we rely upon almost daily that is in terrible need of repair. It is not our own product and the supplier is generally not interested in fixing the problem.
We are ...
- 5,431
17
votes
1
answer
16k
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Difference between bounding box, envelope, extent, bounds?
Every time when I create a script to manipulate vector (point, line and polygon) in python I meet this doubt.
What is the difference between bounding box (bbox), envelope, extent, bounds?
- 1,970
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votes
2
answers
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What are the implications of invalid geometries
I've imported some data in a Postgis database and some of the geometries are reported invalid (ST_IsValidReason reports self-intersection or ring self-intersection).
The queries I am performing don't ...
- 2,358
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votes
5
answers
3k
views
How to snap a road network to a hexagonal grid in QGIS?
I'm trying to use QGIS 2.14 to snap a road network to a hexagonal grid, but I'm getting strange artifacts.
I've created a hex grid with MMQGIS, cells are approx 20 x 23 m. I've buffered the road ...
- 20.5k
16
votes
3
answers
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Exporting only certain columns to CSV file in ArcGIS for Desktop?
I've written a python script using arcpy which outputs a polygon feature class into a File Geodatabase. I have added a function to export the attributes to a separate CSV file. I am using the code ...
- 21.9k
15
votes
5
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856
views
Terminology: Polygon or Area?
When writing about GIS geometry I'm unsure whether to use the term "polygon" or "area".
In particular, does the word "polygon" suggest a specific type of geometry? For example, a colleague suggested ...
- 13.2k
15
votes
2
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Multipoint vs point PostGIS
Is it normal to use the geometry type 'multipoint' instead of 'point' knowing that I use it to store only one point?
How can I convert from multipoint to point?
- 375
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votes
2
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Centroid coordinates for odd-shaped polygons
I have a problem in computing the centroids of certain polygons in QGIS (via the geometry tools): for certain polygons - with a strange and rather long shape - the centroids computed are off the ...
- 181
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votes
5
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Identify polygon containing point with R sf package
I would like to be able to map geocoded coordinates to a region on a .shp file in R using the sf package. I can load up the map and plot it but I am struggling with the code to return the region for ...
- 151
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votes
3
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How to convert from SQL Server geometry BLOB to something else?
I have a CSV data file from a 3rd party that is an exported SQL Server table. They simply did a select * from foo and output the result to a text file and sent it over.
In their table is column of ...
- 151
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votes
5
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Python, shapely library: is it possible to do an affine operation on shape polygon?
I am trying to create a rotated rectangle in lat/lon coordinates.
Basically, I have the coordinates of the center and rotation angle around the center.
Is it possible to do using, shapely or gdal, ...
- 253
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votes
3
answers
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What is "Fix geometries" tool actually doing in QGIS?
Sometimes geometry's have to be fixed for further processing. So you can use "Fix geometries" and it will do the job for you without prompting. But I'm wondering, what the tool "Fix ...
- 8,358
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votes
3
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Calculating a spherical polygon centroid
I'd like a general way to calculate centroids for polygons on a sphere.
So far, the best online reference appears to be:
Tools for Graphics and Shapes by Jeff Jenness.
The method described there ...
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14
votes
2
answers
58k
views
Calculating polygon areas and perimeters using QGIS
Using QGIS, if I load a polygon layer and make a new column, how do I fill that column with the area of each polygon and another column with the length of the perimeter of each polygon?
- 1,005
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votes
4
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In PostGIS: how to split linestrings into their individual segments?
I have one table with many linestrings and I want to make a new table containing the individual segments of all the linestrings, no matter if they are grouped line per line or not.
This is my table, ...
- 353
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votes
4
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Changing (flipping) line direction in QGIS
I have a river network in QGIS. I draw opposite direction of one of the rivers. Now I want to change the direction of that river.
How can I do that in QGIS 3?
(As I know it is flip in ArcGIS)