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.

Filter by
Sorted by
Tagged with
30
votes
5answers
37k views

Fixing geometry validity errors in QGIS?

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 ...
116
votes
13answers
47k views

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 (...
71
votes
7answers
70k views

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 ...
21
votes
1answer
4k views

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 ...
62
votes
4answers
35k views

Visualising WKT geometry string in QGIS

A very simple question: Is there a simple tool in QGIS to graphically visualise geometry formatted as text? Example geometry: "POLYGON((571178 6337246,571178 6402217,598061 6402217,598061 ...
4
votes
1answer
808 views

ArcGis label last vertex Z value

Is it possible to label a feature in ArcMap using geometry values? In this instance I want to label features (polylines) with the Live Z value of the last vertex obtained from the Shape. However ...
6
votes
1answer
1k views

Convert point XY to page units XY using arcpy?

I am using arcpy to export PDFs from my ArcGIS Server application. I want to move a TextElement in my layout view to the centroid of a selected feature. I can get the centroid of the feature, but that'...
21
votes
6answers
59k views

Convert 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 ...
10
votes
6answers
13k views

Moving / offsetting point locations using ArcPy or ModelBuilder?

I have a number non-georeferenced CAD layers (see this question) that have text annotation features. I have created a model to convert the text to points, but after converting the annotation to a ...
15
votes
3answers
42k views

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 ...
37
votes
1answer
34k views

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 ...
19
votes
2answers
8k views

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 ...
11
votes
2answers
3k views

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 ...
22
votes
3answers
11k views

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 ...
11
votes
4answers
17k views

Creating lines from points pair coordinates with ArcPy?

I've got some points pair coordinates (start and end points) which I have to transform into lines. Until now, I used an append of both the coordinates in a pippo.Point(), a pippo.CalculateGeometry() ...
5
votes
2answers
5k views

Multilateration Code

I am currently writing some code to do multilateration using TDOA and currently struggling and wondering if anyone has any reference code that can be used as a test case with some sample data that I ...
4
votes
2answers
573 views

Select the most distant vertex from polygon's centroid using ArcPy

I have a polygon and the polygon's centroid. I want to select the most distant vertex from centroid (picture: point A). I used arcpy.FeatureVerticesToPoints_management to create a feature class ...
9
votes
1answer
16k views

Repairing geometry using QGIS? [duplicate]

I have shapefile with few polygons. Some of them are self-intersecting. In ArcMap I can use "Repair geometry" tool, and it works well. But problem is, that for that task some users need to use open ...
18
votes
5answers
5k 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 ...
14
votes
2answers
11k views

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 ...
8
votes
2answers
4k views

Defining spatial operators (Equals, Disjoint, Touches, Within, Overlaps, Crosses, Intersects, Contains, Relate)?

Ok, I have to admit, I don't really delve too deep into the semantics of the spatial operators list below, I'm more of a user, I write software to drive the SQL most of the time and don't really think ...
17
votes
6answers
12k views

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 ...
11
votes
1answer
4k views

Writing vector layer to CSV file with geometry using PyQGIS?

I use Python try to write vector layer file to csv file with this code: QgsVectorFileWriter.writeAsVectorFormat(mylayer, r'c:\temp\xyz.csv', "utf-8", None, "CSV") It can export to xyz.csv but only ...
7
votes
1answer
3k views

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, ...
3
votes
1answer
136 views

Line width and labels based on blended values of features sharing same geometry in QGIS

I want to appropriate line segments that share the same geometry with a particular line width and labels based on the aggregated values of one field "GIS@BUS_5_Min". My attribute table and polyline ...
13
votes
3answers
6k views

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? ...
1
vote
1answer
52 views

Updating Z values with geometry of multipart and donut polygons with ArcPy?

I am trying to update Z values of polygon features with point features. The code is (found on GIS Stack Exchange) working good if no 'interor ring' or 'multipart' features are present in the polygon ...
19
votes
2answers
6k views

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 ...
9
votes
2answers
1k views

Generating true curve elliptical polygons in file geodatabase using ArcPy?

As background, this question arose from trying to answer a question on How to generate overlapping polygons from lines output from Table To Ellipse tool? Using the ArcMap 10.1 GUI it is very easy to ...
2
votes
3answers
8k views

Creating point at midpoint of polyline with ArcPy?

I have a polyline shapefile (that contains multiple lines) and am trying to create a point at the midpoint of each line using Python. I am currently using the ET Geowizards tool 'PolylineToPoints' ...
10
votes
5answers
4k views

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, ...
2
votes
1answer
552 views

Creating an annulus sector with mapbasic

Knowing the center of rotation, start and end angles, inner an outer radius, how can this be achieved with MapBasic
7
votes
3answers
5k views

How to create a circle in arcpy

Suppose I have a dataset where each record has an x,y and r (the centroid and radius of a circle). How can I create a polygon feature class containing parametric circles? Sorry to those who have a ...
6
votes
2answers
3k views

Determining if collection of coordinates (polygon) is ellipse?

I'm attempting to determine a geometry type based on a collection of coordinates and have come across a situation where I'd like to differentiate between what is a "polygon" and what is an "ellipse". ...
4
votes
2answers
4k views

fixing polygons with “ring not closed” errors

I have a shapefile with a single Polygon feature. This feature has a "ring not closed" geometry error (seen here in QGIS): I tried using buffering and the GRASS v.clean command as suggested in other ...
4
votes
3answers
2k views

Copy geometry from one layer onto attributes of another?

I have two polygon layers, A and B, that have the same features but totally different attributes. I want to use the attributes from layer A, but I want them to have the more accurate geometry from ...
2
votes
2answers
1k views

How to handle coordinates accuracy in ArcGIS

I am creating very basic rectangular polygon using very basic a Python code nCols,nRows=100,100 corners =[[0,0],[0,nRows],[nCols,nRows],[nCols,0],[0,0]] p=arcpy.Polygon(arcpy.Array([arcpy.Point(*...
2
votes
1answer
2k views

How to perform a cascaded combine from python script in QGIS?

I'm working with a large dataset, and I need to be able to combine up to 400,000 polygons. I have been using the QgsGeometry::combine(QgsGeometry* geometry) function and simply looping over all ...
21
votes
1answer
19k views

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": "...
22
votes
2answers
10k views

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: ...
15
votes
3answers
12k views

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 ...
11
votes
2answers
6k views

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 ...
26
votes
4answers
75k views

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/...
13
votes
5answers
579 views

What in-depth spatial database systems tutorials exist? [closed]

Is there a good tutorial that explains in depth the internals of a GIS and a spatial database system such as PostGIS with examples and without any background assumption? I'm specifically looking for ...
11
votes
2answers
3k views

How to compute Straight Skeletons using Python?

Is there a Python package which provides an implementation of a Straight Skeleton algorithm? I'm aware that the open source (C++) project CGALcontains an implementation but it seems like cgal-...
15
votes
3answers
39k views

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:...
8
votes
3answers
2k views

Retrieve polygon smallest MBR

I have a postgis table containing polygons. I want to transform my polygons to 4 points polygons : retrieve the smallest MBR. Here comes an illustration of what I want : My original polygon is in ...
5
votes
3answers
3k views

fTools-Error: “…invalid geometry…”

I want to intersect contours with polygon like in the image below. But I got this error: Warnings: GEOS geoprocessing error: One or more input features have invalid geometry. Some output geometries ...
19
votes
3answers
3k 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 ...
16
votes
1answer
10k views

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 ...