Where features overlap

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17
votes
4answers
5k views

Separate polygons based on intersection using PostGIS

I have a PostGIS table of polygons where some intersect with one another. This is what I'm trying to do: For a given polygon selected by id, give me all of the polygons that intersect. Basically, ...
14
votes
4answers
2k views

PostGIS: Select features that do NOT intersect

This seems to me like such a simple question (and it probably is) yet I cannot seem to find an example that gives me the answer. Using PostGIS, I just want to select points that fall outside of ...
14
votes
2answers
2k views

Identifying road intersections using PostGIS

I'm trying to identify where roads intersect each other, and to make a point at this intersection, with the number of roads that form the intersection listed. I was wondering if there was some way ...
13
votes
6answers
6k views

How to use ST_Intersection?

Here's a quick summary about what I'm trying to do: I have 3 tables in Postgres, 'a' and 'b', each have a Polygon column, and 'c' has a Point column. What I'm trying to do here is to get the ...
8
votes
4answers
1k views

Best way to find the polygons crossed by a line

I'm trying to find all the polygons crossed by a single line (a GPS track). I'm using the OGR library (from python) for computing this, but it's currently a bit 'brute-force' (and slow). For every ...
8
votes
4answers
3k views

Lines that intersect vs. Lines that touch - how to distinguish?

How do I distinguish between these cases in ArcGIS 10? I am looking at the Trim Line function but that's not what I want (destructive). Case 1: Both endpoints of a line touch another line Case 2: ...
7
votes
3answers
2k views

Extract Overlapping Polygon Data to Points

I have a polygon data set of corn yield collected by a combine. However, as the combine drove through the field, there was slight overlap between passes, leading to overlapping polygons within the ...
7
votes
1answer
513 views

Find Nearest Line Segments to Point

Background From a known Point, I require to establish the nearest surrounding "visible perimeter" against a table of MultiLineStrings, as shown on the diagram. I've searched this site with a number ...
6
votes
7answers
2k views

Intersection algorithm that correctly handles the 180° meridian and poles?

Is there a well known intersection algorithm that correctly handles 180 meridian and poles? For example, let's say we have a list of latitude and longitude values that represent Antarctica. Let's ...
6
votes
1answer
3k views

can I extract overlap of polygons within the same layer?

I am trying to extract the overlap of polygons that are within the same layer in 10. The layer came from a buffered street centerline and I'm trying to extract and delete the intersections from the ...
6
votes
1answer
754 views

Intersection of multiple layers in PostGIS

I need to write PL/pgSQL stored procedure for calculation of intersection of multiple layers. For example, for three layers A, B, C this function should return ABC geometry: Function takes as input ...
6
votes
2answers
5k views

How to create a new layer from overlap between two layers?

I'm new to desktop GIS, and will try to ask while lacking the proper terms from the GIS lingo: If QGIS was like Photoshop I would like to make a selection from one layer, and then match that ...
5
votes
1answer
2k views

How to get the intersecting polygon of two polygons? (using JSTS intersection)

I want to intersect two polygons within an OpenLayers layer. I found the JSTS library, which should be able to intersect two polygons, and return the new created polygon of the intersection. The ...
5
votes
2answers
433 views

Best strategy for polygon search?

I have a fairly simple question. What is the best strategy to do the following scenario? I think this is a very common scenario: I have a several thousands of dataset with polygon/points. Each ...
5
votes
3answers
317 views

Trying to combine nearby points into a polygon

We have collected millions of cell phone strength readings. I am trying to group points of the same strenght that are within a distance of each other in to a polygon. I asked on the postgis mailing ...
5
votes
1answer
230 views

Intermediate points on a small circle

I need to interpolate lat/lon points along a small circle, with a given centre and radius. I've successfully used these formulas for great circles. What is the equivalent for small circles?
5
votes
2answers
2k views

Calculate area of intersecting polygons in QGIS

I have two collections of shapefiles: 1 - postal codes, administrative and political areas 2 - various land use categories like parks & allotments, and points like trees I want to produce ...
5
votes
1answer
521 views

Split polylines at polygon boundaries in QGIS

I have a set of contour lines and a polygon set containing glaciers. Because I want the glaciers to have blue contours, I need to split the contour lines at the glacier boundaries. I can achieve this ...
5
votes
1answer
113 views

Simulating Random Agent Movements along Roads on Map

I need to simulate agent movements on map as follows: Agent starts a known location and moves along a road. At each road intersection, the agent uniformly chooses one possible road and moves along ...
5
votes
1answer
392 views

adding multiple points to a linestring in PostGIS

Though a newbie to PostGIS, I'm having trouble solving something that I think should be farily straightforward. I have two linestring tables, both consisting of simple, 2-node line objects: one has ...
5
votes
2answers
1k views

Need help calculating forest cover within a buffer when it overlaps with other buffers

I'm new to ArcGIS and having real trouble getting this done… Hopefully someone can help. Thanks in advance! I have a layer showing forest cover in a landscape. I'm trying to create a 5km buffer ...
5
votes
1answer
322 views

Intersect between Surface and Ray

I am interested in finding the intersection of a Ray and a Surface in ArcObjects. I already know of two solutions. First solution is to use the Locate method of ISurface: Dim intersectionPoint As ...
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
1answer
269 views

Performance in calculating raster statistics in PostGIS

I'm trying to calculate raster statistics (min, max, mean) for each polygon in a vector layer using PostgreSQL/PostGIS. This GIS.SE answer describes how to do this, by calculating the intersection ...
5
votes
1answer
662 views

ArcGIS Intersect using Geometry Service

I am using the intersect service from the ArcGIS Geometry service. referring : http://help.arcgis.com/en/webapi/sil....htm#Intersect I have modified it to make it work with polylines it works fine to ...
5
votes
1answer
465 views

Apportioning Points at a street intersection (arcgis or mapinfo)

I can't seem to find any evidence of this question, but I'm surprised by that, so pardon if this has been asked. If one is mapping crime location reports, by XY coordinates to streets, to create ...
4
votes
2answers
121 views

Creating space at intersection of two links

I have a shapefile consisting of two links which are crossing over each other. I want to create an empty space at the point of intersection of the two links. As of now, I have been manually doing ...
4
votes
2answers
445 views

How to select features that intersect but don't touch (using ArcObjects)?

So how do I do that? ArcMap's Select By Location selects also all features that touch, but I only need the ones that actually intersect the area. I currently use ...
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 ...
4
votes
2answers
283 views

No intersection found between polygons I know intersect!

I'm using two geographies: one is made up of small areas (about 2200), the other large areas (about 70). Both cover all of Australia, and the small areas are not necessarily nested inside large areas. ...
4
votes
1answer
1k views

PostGIS geometry intersection test results different for Point and Linestring

Can anyone please tell me what I'm doing wrong, and how do I avoid the problem? I'll attempt to clarify what I'm doing as things go along. The geom column is a multipolygon column, all values are ...
4
votes
2answers
964 views

How to Intersect between a vector (administrative areas) and a raster layer (slope)?

What I've got: 1: A vector-layer with administrative areas of my country 2: A raster-layer with the slope of the terrain of the same country (it is derived from SRTM elevation data with QGIS) What ...
4
votes
1answer
554 views

Spatial Join in PostGIS according to Line Attribute

I am in the process of building a data warehouse in PostGIS, that will store the length of the road network of a country (Lines) per Administrative Area (i.e. Province or State, referred to as AA ...
4
votes
1answer
362 views

How to use the Intersects function in the Field Calculator of QGIS?

I would like to have an example on how to use the Intersects function in the Field Calculator of QGIS. Basically, I want to know which feature from a polylines layer intersects a polygons layer and ...
4
votes
1answer
912 views

How to find all intersections and count lines arriving at each intersection?

I'm having a hard time getting off the ground with this, and am trying to move away from ArcGIS / arcpy. I have a shapefile with a network of polylines. I want to find/count all 2-way intersections, ...
4
votes
2answers
530 views

is there a way to tell if two linestrings “really” intersect in JTS or GEOS

In JTS (or GEOS) you can't tell if two linestrings really cross each other. The result is exactly the same whether the lines simply have a point in common but don't cross or if they really cross. Is ...
4
votes
2answers
152 views

How to optimize a ST_Within query to count lightning occurrences inside a country?

I just started learning PostGIS, and right now i'm trying to count the number of lightning strikes in my country (Brazil in this case). I have the following tables: earth_feed --> This holds the ...
4
votes
1answer
491 views

Obtain voronoi polygons which extend till the boundary of another polygon

I have certain hubs (coloured yellow) in a district (coloured light blue). I need to find polygons indicating the closest hub to every point in the district. The voronoi polygons that I obtained ...
4
votes
2answers
281 views

Keep nonintersecting polygons during clip

I am using ArcMap 10. I have two datasets, one of which consists of many small contiguous polygons, and one which has many small non-contiguous polygons. The first dataset is census blocks, and the ...
4
votes
1answer
699 views

Line intersection with circle on a sphere (globe or earth)

How can I find the intersection point of a line and a circle on a sphere (on earth) Please, if any one knows a good solution help. Thanks in response :)
4
votes
1answer
354 views

automating forest cover calculations with Python

I have a layer of forest cover comprising ~ 30,000 individual forest patches, and I need to calculate the amount of forest cover within a 5 km buffer of each patch. The buffers all overlap each other, ...
4
votes
1answer
422 views

How to split a polygon using R

I have an irregular polygon which is a spatial object. I want to divide it into multiple polygons (say, n=25) with equal height. To show how I want to divide it, I've plotted grids on the ...
4
votes
2answers
1k views

OpenLayers - Get features inside a polygon

In my OpenLayers map I allow users to draw an ad-hoc polygon vector. Then I need to get all the features from a WFS vector layer that fall within the ad-hoc polygon. Here is the code I have that ...
4
votes
1answer
280 views

Finding intersection density for weighted lines connecting points across the continental USA

I'm working on an one-time problem that I'm hoping to solve with a computer program using free GIS libraries (preferably for VB.Net, C#, or Python... Java or C/C++ could work too). Alternatively, I ...
4
votes
0answers
167 views

Cut polygon and retain data

I have these two polygons: library(sp); library(rgeos); library(maptools) coords1 <- matrix(c(-1.841960, -1.823464, -1.838623, -1.841960, 55.663696, 55.659178, 55.650841, ...
4
votes
0answers
330 views

Rgeos drops associated values when intersecting polygons

I am trying to intersect two SpatialPolygonsDataFrames and get a SpatialPolygonsDataFrame as the result. Unfortunately, using the gIntersection function from rgeos (which works impressively quickly ...
3
votes
3answers
1k views

How to find if two polygons Intersect in python?

I'm looking for an algorithm, high level solution, or even a library which can help me determine if two polygons intersect, in Python. I have the vertices of the two polygons (These are single part ...
3
votes
2answers
154 views

geospatial libraries like postgis

I'm pretty comfortable with postgis, but I realized that for part of my application, having a database is pretty heavy. I'd like to be able to take a stream of Point objects and check against an in ...
3
votes
2answers
1k views

Is there a way to get at C's OGRLayer.Intersection() or OGRLayer.Clip() in Python?

I am working with OGR in Python and noticed that the C libraries have useful Intersection() and Clip() functions as part of the Layer class. Is there any way to get at these functions in Python? I ...
3
votes
3answers
186 views

Is the Intersection Operation Commutative?

In map overlay, is intersection of map layers a commutative operation ie layer_A intersection layer_B = layer_B intersection layer_A? If layer A is a square and layer B is a triangle. In this case, (A ...