On a map, a closed shape defined by a connected sequence of x,y coordinate pairs, where the first and last coordinate pair are the same and all other pairs are unique.
7
votes
1answer
694 views
How to select WFS features by polygon in OpenLayers?
I need to be able to select features on a wfs layer using a polygon instead of a box. I was hoping this would be a standard option in the SelectFeature class. Too bad this isn't the case.
Any ...
7
votes
1answer
767 views
Should I split MultiPolygons into Polygons?
In the system I'm implementing I have a table T1 with an associated geometry. Most of the geometries are a set of n polygons, with 10 < n < 100.
At the moment in the table T1 I have a geometry ...
7
votes
1answer
209 views
How to rectify polygon-shapes in Quantum-GIS? [duplicate]
I have some polygon-shapes in qgis-1.7.0 and want to ensure that every polygon is a rectangle. See image below.
Is there any way I can do this in quantum-gis (or any other f/oss)? Or how can I ...
7
votes
3answers
411 views
Creating regularly spaced, defined # of points within polygon in QGIS
I used the research tool "Regular Points" to produce a certain number of points within a polygon, but it forms a rectangular grid of points rather than only within the shape of the polygon. Since I ...
6
votes
2answers
134 views
Breaking apart a polygon layer by unique values, creating many new layers
I have a large dataset of habitat information that I need to calculate distances from animal locations to the closest polygon of each habitat type. The way to do this, that I understand, would be to ...
6
votes
4answers
435 views
Exporting polygon features to individual image pngs
I have a shapefile with a few thousand polygons, ArcGIS [9.3] (and even PostGIS). I would like to export each of those polygons into its own thumbnail image file without any real context. What is the ...
6
votes
2answers
431 views
Converting point sets to polygon boundaries
I'm trying to convert sets of points to their respective polygon boundaries. I think this is something like a Voronoi diagram or Convex Hull, but not quite. I'm sure there's a technical term for it, ...
6
votes
5answers
1k views
Algorithm to find polygons enclosing points
I'm trying to find an algorithm that can determine the smallest possible polygons to cover a number of points.
I know how to get the convex hull around all the points, but say that the points are ...
6
votes
1answer
3k views
How to convert a String to OpenLayers.Geometry.Polygon using javascript?
First let me say that I'm using Javascript, jQuery, Java, GeoServer, OpenLayers and PostGIS.
Using java class ResultSet I return this String:
POLYGON((516000 2135000,515039.264020162 ...
6
votes
1answer
312 views
Filling a polygon with lines using Postgis
i need to calculate a specific distance in an area. The distance is calculated from parallel lines in a polygon, And i need to find out how many parallel lines (with x meters distance to each other) ...
6
votes
2answers
68 views
summing up over an area based on a distance related function
Through a field study, we learned that the density of a bird species in the forest was related to the distance to forest edge: ln(density) = 1.89*(distance to edge) + 0.34
Now, for any forest ...
6
votes
3answers
648 views
Can Polygons be generalized to MultiPolygons in GeoDjango?
I set up a model with models.PolygonField in geodjango, using postgres as database. I try to import shp into postgres. The problem is, shp (compiled with QGIS) mixes polygon and multipolygon, hence it ...
6
votes
4answers
642 views
Output PostGIS geometry data as centroid or polygon depending on zoom level (GeoServer)
This is what I want: when I zoom out, cities of the country should appear as points and at a certain level when I zoom in, I want them to appear as polygons (showing the area of the city and ...
6
votes
1answer
533 views
Where can I find a Unesco World Heritage List as boundaries?
I was wondering if anyone knows where to find the UNESCO world heritage list with boundaries? I can extract point data from the json feed for the map on the website http://whc.unesco.org/en/list via
...
6
votes
1answer
169 views
Efficiently identifying overlapping polygons with Python
I'm parsing the NOAA severe weather alert feed and using it as a datasource for a weather alerting system.
In the feed, I occasionally find a polygon entry for an alert. Unfortunately, counties that ...
6
votes
1answer
183 views
QGIS define hexagon area around mapped points
I am using QGIS to map a number of radio antennas (for mobile network).
Once I have the layer of the sites (done), I would like to assign to each site a coverage area (envelope). I could achieve that ...
6
votes
2answers
1k views
Create a polygon layer from point data
I'm currently using QGIS 1.8.0
I would like to create a polygon layer from a point dataset, where the size of the polygons relates to the resolution of the grid reference.
The ultimate aim would be ...
6
votes
3answers
574 views
How best to fix a non-noded intersection problem in PostGIS?
I'm using a PL/R function and PostGIS to generate voronoi polygons around a set of points. The function that I am using is defined here. When I use this function on a particular dataset I get the ...
6
votes
1answer
192 views
How to draw shapes with highest possible decimal accuracy
I am trying to read input of lat and long to draw the shape based on condition.The input is standard array of lat and long with 15 decimal accuracy. I am realizing - I am loosing some decimal accuracy ...
6
votes
1answer
747 views
How to eliminate gaps in the ArcGIS union operation?
I have a layer that has nested polygons in them. I want to aggregate the polygons. I do this using the Union function.
I use the "No Gaps" option when I perform the union.
However, when I overlay ...
6
votes
1answer
47 views
Is there a way to select only a certain polygon for editing?
I have a spatialite data base with 4300 polygons contained within. I wish to be able to edit the polygons but once i have highlighted the Polygon from the attributes table i find it hard to edit the ...
6
votes
1answer
195 views
Generalize large polygon-file
I have a large polygone file with landuse information (6 classes). Its vectorised from a raster classification so the polygons are all angular. Any of my tries to generalize with v.generalize (sneaks, ...
6
votes
3answers
225 views
What geometric attributes do polygons possess, and how can these be used to filter features?
Given a polygon featureclass containing many polygons of different sizes and shapes, which geometric attributes (area, perimeter, etc) could be used to filter the polygons? It's probably best to ask ...
6
votes
1answer
154 views
Can you permanently set the polygon/polyline segment length?
I'm trying to create a several hundred polygons in ArcGIS 10, each of which may have up to several hundred vertices. For consistency sake I would like each line segment in these polygons to be of a ...
6
votes
2answers
1k views
Openlayers geometry: how to convert area from degrees to square kilometres?
I get a multypolygon from my web service and want to calculate the area of that polygon. I was trying to use this piece of code:
var poly = new OpenLayers.Geometry.MultiPolygon(poligon);
var area = ...
6
votes
2answers
151 views
How do different GIS systems determine a Polygon's interior?
I'm interested in understanding how real-world GIS systems and their data encode Polygons.
Specifically, how do they resolve the ambiguity of a Polygon's interior on a sphere?
Background: in 2D, ...
5
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 ...
5
votes
1answer
698 views
How to calculate the size of a particular area below a buffer in QGIS
I have a point shapefile of villages where data was collected in Northern Kenya. I created a buffer around those villages.
The second vector layer contains polygons defining areas according to ...
5
votes
3answers
1k views
Why doesn't the split tool return any records in the attribute table?
I've been trying to split a large land use shapefile using a set of study area polygons as the split feature, but when the function finally finishes running (the land use dataset is quite large), all ...
5
votes
3answers
364 views
How do I use polygons to apply a unique value to all raster cells within those polygons?
In ArcGIS 9.3, I have a raster file that I would like to "mask" with polygons, giving a single value to all the raster cells that overlap the polygons. How can I do this? Here's a screen shot, where ...
5
votes
2answers
322 views
Proper way to rbind SpatialPolygonsDataFrames with identical polygon IDs?
What's the proper R idiom for rbinding SPDFs together when the IDs overlap? Note that here (as is often the case) the IDs are basically meaningless so it's pretty annoying that I can't just make ...
5
votes
2answers
1k views
How to disable polygon Label on the vertices (OpenLayers) in Edit Mode
I added the style on the polygon layer like so.
var style = $.extend(true, {}, OpenLayers.Feature.Vector.style['default']); // get a copy of the default style
style.label = "1233456 ha"
...
5
votes
3answers
248 views
Selecting polygons by number of sides
I'm using ArcGIS 10 to build some figures for a journal article. One is a figure of an unstructured finite element mesh of triangles spanning the western Atlantic Ocean. I exported this mesh from ...
5
votes
2answers
1k views
Convert Long and Lat Co-ordinates to Square Miles
I have a set of Long and Lat co-ordinates making up a five point polygon which I have converted in excel using the following formula:
...
5
votes
2answers
99 views
inner convex-hulls in a set of 2D points
A set of 2D Points are scattered randomly (i.e., no specified pattern), we are interested in finding all inner-convex-hulls (ICH) in an order of largest in area to a minimum until the entire study ...
5
votes
4answers
203 views
How to avoid holes in polygons from lines?
I am trying to convert a dataset of lines that contains the coast of New Zealand into a big polygon.
However using the vector -> geometry tools -> lines to polygon command in Quantum GIS results in a ...
5
votes
3answers
955 views
How can I display with OpenLayers the geometry returned from a ST_Buffer in POSTGIS?
Im using PostGIS, GeoServer and OpenLayers, and the thing is that i want to display the geometry result from a query like this:
SELECT ST_Buffer(ST_GeomFromText('POINT(100 100)'), 500);
To perform ...
5
votes
2answers
291 views
How to achieve an “inner glow” effect on polygons drawn using the Google Maps v3 javascript API?
Is it possible to produce an "inner glow" effect on polygons drawn using the Google Map v3 javascript API?
If not possible using the vanilla Google Maps API, is there a 3rd party tool that can do it? ...
5
votes
1answer
688 views
How to persist a polygon to SQL Server database and vice versa?
How do I extract all the points from a Polygon drawn in ArcMAP and then persist that data into a SQLServer database table containing a geometry column and then when I've got the data persisted read ...
5
votes
2answers
106 views
Need an Algorithm to Determining Polygon Borders
I'm currently writing a program in Java and I'm dealing with polygon objects. I want to create a different color border between touching objects depending on their class (i.e. land, ocean, etc). I ...
5
votes
2answers
630 views
How to smooth large vector polygons from Raster
I have a landuse classification raster file (6 classes) of a large area. But I need it in vector polygons so I vectorised it. No problem so far, but the result is - of course - that every pixel is ...
5
votes
1answer
136 views
Create a new vector layer that fills space between other polygons in QGIS
I inherited a clipped (500m radius) land cover map containing vector layers of different land cover categories such as buildings, grass, roads, etc from a colleague.
The empty (white) space in ...
5
votes
2answers
274 views
How to enclose clustered points with polygon?
I have a raster with forest (1), no forest (2) data. "1" is represent single/few trees and there is gaps between them. I want to create a polygon around these trees to a forest map. It is not a dense ...
5
votes
3answers
685 views
How to interpolate into polygons?
I need to interpolate values from points to polygons.
I have a point shapefile and a shapefile of adjacent polygons. Some polygons get several points falling inside, some have nothing.
I thought ...
5
votes
1answer
991 views
Count number of unique raster pixels in polygon using ArcMap?
I have a polygon shapefile and I want to generate a table of a count for each pixel value in each polygon. My main goal is to find out what pixel is most abundant in each polygon. I am using ArcMap ...
5
votes
2answers
695 views
Finding parcel polygon features with frontage on multiple streets
The Department of Public Works would like to know how many properties in the city have a sidewalk at both the front and back. To get at this, I'm looking for a method to find parcels with frontage on ...
5
votes
2answers
333 views
How to sum pixel values within a polygon zone in QGIS?
I have two layers: a raster layer and a vector layer (polygon). I can see the values of the raster pixels but I don't know how to combine them with information from the polygon layer. More ...
5
votes
1answer
71 views
How do you edit a stack of polygons simultaneously?
Using ArcMap 10.1.
Lets say you have 100 polygons that all are in the exact same shape and in the exact same place. They appear to be one polygon. How would you edit the shape of all 100 at the same ...
5
votes
1answer
64 views
Geographic locators within Polygons
I have a list of geographic locators and a boundary file. In QGIS, is there any way merging them together to create a lookup saying this boundary contains these locators? Not the number the actual ...
5
votes
1answer
125 views
How can I increase performance on inserting features with polygon geometry?
I have a problem when inserting features with polygon feature class in FGDB. This is my code:
... initialising some fields (does not affect performance)
m_featureBuffer.Shape = ...
