(1) abstract geometry; (2) storing geographic data in projected coordinates; (3) a generic ESRI term for vector features; a class for "geometry" objects.

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58
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15answers
19k views

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 ...
26
votes
4answers
6k 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) ...
31
votes
4answers
5k views

What are the pros and cons of PostGIS 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 ...
11
votes
4answers
2k views

Comparing two Digital Elevation Models (DEMs) from LAS files?

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 want to compare how the Digital ...
28
votes
1answer
7k 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 ...
24
votes
3answers
6k 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 ...
10
votes
3answers
13k 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 ...
4
votes
2answers
273 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 ...
18
votes
4answers
2k 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 ...
9
votes
2answers
1k 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 ...
17
votes
3answers
3k 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 ...
5
votes
5answers
1k 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
3k 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 ...
13
votes
5answers
405 views

What in-depth spatial database systems tutorials exist?

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 ...
6
votes
3answers
768 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 ...
5
votes
2answers
1k 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 ...
4
votes
2answers
3k 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 ...
6
votes
3answers
1k views

How to fill a hole in a multi-polygon layer on QGIS 2?

I need to fill a hole in a multi-polygon layer on QGIS 2.0. I've set the snapping option for the layer as follows : mode: to vertex and segment tolerance 4 pixels avoid intersection "enabled" ...
2
votes
3answers
321 views

Polyline selection of features with angle turns up to a specified angle

I'm looking for an automated way to select line features that have specified angle between vertexes. That in order to check water mains layer -steel pipes can have only 45 or 90 degrees turns and I ...
2
votes
1answer
428 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 ...
7
votes
2answers
758 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 ...
7
votes
3answers
2k 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 ...
3
votes
2answers
3k views

How to remove duplicate features with the 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 ...
3
votes
2answers
588 views

How to find self-intersecting polylines using ArcObjects?

If I have a polyline, how do I figure out whether it is self-intersecting? I tried to use ITopologicalOperator.IsSimple Property, but it always returns true. Are there any ways of doing these kind ...
3
votes
2answers
632 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 ...
2
votes
1answer
157 views

QGIS 2.2 rendering problems

i have a problem with some geometry. When i run the check geometry validity i get an error coming back that the rings are not closed, so recangular forms that i have surveyed are showing up as ...
1
vote
2answers
431 views

ST_DWithin uses Geometry or Geography type

assuming I use the following query to match the locations to a poi within 10km distance: SELECT poi.poi_id, h.loc_id, (ST_Distance(poi.geom,h.geom)*111.111) as distanceinkm FROM iut_poi_transl AS ...
0
votes
1answer
674 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 ...
16
votes
2answers
4k 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: ...
11
votes
2answers
1k 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 ...
12
votes
4answers
1k 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 ...
12
votes
2answers
3k views

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 ...
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 ...
9
votes
1answer
6k views

How to create a script tool that will create a copy of a feature class and offset it by a given distance? (arcpy)

I want to duplicate a polygon feature class and offset all of the polygons by about 10 feet in both the x and y directions. I asked if there was any way to do this last week, and I was informed that I ...
5
votes
2answers
5k 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?? ...
1
vote
2answers
3k 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", ...
11
votes
4answers
392 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 ...
8
votes
1answer
281 views

How to rank polylines according to their similarity to a ref polyline?

How to rank polylines according to their similarity to a ref polyline? Update 1: simulations show that simple $\sqrt{\sum{(case-ref)^2}}$ can find better similarity between polylines (as set of ...
8
votes
6answers
1k 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 ...
5
votes
1answer
222 views

Can ArcPy 10.1 be used to generate true curve elliptical polygons in a file geodatabase?

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 GUI it is very easy to ...
5
votes
1answer
720 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 ...
4
votes
1answer
137 views

Configuring Geoserver to use a specific postgis geometry column as the default

I have a PostGIS table with two geometry columns, both multipolygon but one with SRID 4326, the other 3857. When publishing the table in Geoserver, I realize that Geoserver defaults to using the first ...
3
votes
2answers
2k views

Extracting elevation from a TIN file with a point shapefile overlay

I have a TIN file that was built off of contour polyline shapefile (I think). I have a point shapfile with a few points. How can I extract elevation of the TIN file where the points occur? I am ...
2
votes
2answers
1k 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
0answers
88 views

Invalid geometry

I'm working on some shapefiles in both ArcGIS 10.2 and QGIS 2.0. I have 3 files which I have cleaned of self intersections in ArcGIS using Repair Geometry. I have also checked for Overlaps using the ...
9
votes
4answers
263 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
405 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 ...
5
votes
1answer
1k views

How do I find the intersections of 2 circles on earths surface?

I have the circles' center in lat & long, as well as the radius in meters. How do I find the circles intersections? Edit: EXAMPLE: Circle 1: Center on Earth's surface (43.564627,-116.220524) ...
5
votes
2answers
278 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 ...
3
votes
2answers
519 views

How to densify a polyline according to a specific length? [duplicate]

Possible Duplicate: Add vertices to lines I am using QGis 1.8.0 I would like to densify a polilyne according to a particular length of segment (ex. 200 m). I know it is possible with other ...