(1) abstract geometry; (2) storing geographic data in projected coordinates; (3) a generic ESRI term for vector features; a class for "geometry" objects.
51
votes
12answers
12k views
Concave Hull: Definition, Algorithms and Practical Solutions
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 ...
22
votes
4answers
2k views
PostGIS: What are the pros and cons of geography and geometry types
My company uses geometry (the_geom) data type for storing geospatial data.
I've recently been acquainted to the concept of geography (the_geog) data type which, as I understand it, stores the SRID ...
21
votes
1answer
2k views
How to find the center of geometry of an object?
Well it might be a simple question. Given a set of 2D or 3D points, the question is:
How to find the center of geometry of an object?
According to the following figure, the center of geometry ...
19
votes
3answers
2k views
How to find the minimum-area-rectangle for given points?
The following is another problem that I am working on it these days.
As you see in the figure, (BTW, I tried to make it self-presenter) the question is:
How to find the minimum-area-rectangle (MAR) ...
15
votes
3answers
2k 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
...
16
votes
4answers
829 views
Generalisation Strategies for Building Outlines
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 ...
8
votes
3answers
6k views
How to convert .shp to .csv including attributes AND geometry?
I have a .shp file 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 ...
15
votes
3answers
2k views
Find 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 ...
8
votes
2answers
628 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 ...
6
votes
3answers
616 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 ...
9
votes
4answers
891 views
comparing two DEMs
i have two Lidar las files, one is original let's say with X points. And the other is copy of the first las file but with Y points, where Y is less than X. Now, i wanted to compare how the Digital ...
5
votes
5answers
768 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, or ...
4
votes
1answer
1k views
Transforming geometry coordinates from SRID 4326 to SRID 3011
In SQLServer geometry field, I want to change the coordinates of geometry from one spatial reference system to another spatial reference system (from SRID 4326 to SRID 3011) by using ST_Transform. But ...
3
votes
2answers
414 views
How do I find the points of intersection between a small circle and a great circle?
I only actually need to intersect a great circle arc i.e. the shortest path between two points, with a given small circle.
I found this tutorial for intersecting two great circle arcs, but ...
0
votes
1answer
292 views
ArcGIS/arcpy: Can a variable be set to reference an in_memory workspace object?
This is an offshoot question related to a question I posted earlier. I have the following arcpy code that inputs a Python list of polygon geometry objects to the Union_analysis tool, which then ...
14
votes
2answers
2k 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:
...
12
votes
4answers
514 views
How can one compare two geometries in arcpy successfully?
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 ...
10
votes
2answers
3k views
Point (of a linestring) within Polygon using ogr and Python
I'm currently working on a project in which I need to build a topological network out of the geometry features I find in shapefiles.
So far using Ben Reilly's open source project I've managed to ...
4
votes
2answers
2k views
Find closest lat long to an input lat long (SQL Server 2008)
I have a point cloud in my database (SQL Server 2008 spatial). That is about 6 million records. There are 3 columns: id, value, geom. What is the optimal way of getting the 'value' at input lat long??
...
2
votes
2answers
792 views
How to repair topology of a shapefile?
I performed an object-based image analysis using ENVI EX, and each of the classified features were exported as a shapefile. I transferred those shapefiles into ArcMap 10, and tried to intersect them ...
11
votes
4answers
309 views
Given a list of surveyor points, what is the algorithm used to simplify the points and retain the terrain characteristics?
Given a terrain and surveyor points sampled from from it or from its contours, is there any algorithm that one can use to simplify the points ( i.e., reduce the surveyor points number) and at the same ...
5
votes
1answer
460 views
Get shortest distance between two geometries in ArcPy
I'm using ArcPy and using a cursor to step through one polygon feature class. For each of these 'source' polygons, I am creating a SearchCursor to find all polygons in a second feature class that ...
2
votes
2answers
401 views
Downloading Google Maps municipal geometry
When searching for a city on google maps, google is that smart it displays a geometry line on the boundary off the municipal.
See this link: http://g.co/maps/23dz5
Is there a place in the google maps ...
1
vote
2answers
1k views
How to initialize a WFS Layer?
Here is the code block (the layers are stored in Oracle database):
var saveStrategy = new OpenLayers.Strategy.Save();
var adresspt_wfs = new OpenLayers.Layer.Vector("Address points WFS", ...
9
votes
4answers
232 views
Is there a standardized or “most used” dummy Z value?
Creating and importing both 2D and 3D data, I have many times encountered the situation where I have no Z value for a coordinate set, that the value of a Z coordinate seems out of range (like -99, ...
9
votes
1answer
305 views
Performing Overlay of Two Triangulated Irregular Networks (TIN)
I am referring to the paper here, section 2.6.1, on the adding and subtracting of two TINs:
The addition of two TINs can be
determined exactly and stored into a
new TIN, because the addition ...
8
votes
6answers
851 views
Real-world example of Affine Transform?
From the Wikipedia article:
In geometry, an affine transformation or affine map or an affinity (from the Latin, affinis, "connected with") between two vector spaces (strictly speaking, two affine ...
7
votes
2answers
300 views
Growing a PostGIS geometry by a percentage
I'm looking for a way to add a buffer around a PostGIS geometry, but the size of the buffer should depend on size of the geometry. That is, I want each geometry to be enlargened by, say, 5%.
The idea ...
5
votes
2answers
222 views
Does the Chamberlin trimetric projection map (some) great circles to straight lines?
I know that, in general, the Chamberlin trimetric projection maps most great circles on the sphere to some sort of non-straight curve on the flat map.
But what about the 3 special great circles ...
2
votes
1answer
257 views
The minimum bounding circle of geometry that crosses the 180th meridian
Background: I've been given a task where I have to calculate the minimum bounding circle of Alaska (for the purpose of running a Roeck test). I'm using the Census' state level geometries available ...
1
vote
1answer
572 views
How to create multipart line and polygon with interior ring in ArcGIS Python?
My objective is to swap X,Y coordinates of feature classes using Python and arcgisscripting.
Based on help examples, I managed to write script which reads and writes all geometry types.
The problem ...
0
votes
1answer
388 views
ArcGIS/arcpy: Input of in-memory geometry object to Dissolve tool in arcpy script throws Error 000732, input doesn't exist or is not supported
In an arcpy script, I run a Union on a list of geometry objects. The output is set to an empty geometry object. The Union runs fine. What I am trying to do is then feed that output into the ...
0
votes
1answer
983 views
C# library for converting geom field of SQLServer into set of google latlng
Is there any C# library which can convert the geometry field into set of google latlngs? I have stored a shapefile into SQLserver table. From Sqlserver i want to read the geometry field data and want ...
