PostGIS is an extension for the PostgreSQL object-relational database that adds support for geographic objects.

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9
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2answers
2k 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 ...
8
votes
3answers
3k views

How to emulate Google Maps driving directions using pgRouting?

Would like to emulate google maps' driving directions functionality but use pgRouting instead. google's data over the project area & scale is quite a bit off so we want to use our own transport ...
4
votes
4answers
4k views

Live KML from PostGIS to Google Earth

I was wondering if anyone knew a way to bring data from a postGIS database into Google earth to view live. I know of the asKml function in PostGIS, but I'm interested to know if anyone had managed ...
18
votes
2answers
7k 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: ...
16
votes
2answers
4k views

How can I calculate the bearing between two points in PostGIS?

How can I find the bearing between two points in PostGIS? Please specify in your answer whether or not the method producing a bearing on the spheroid, or a planar bearing.
2
votes
4answers
5k views

struggling with GeoDjango install: ERROR: could not access file “$libdir/postgis-1.5”: No such file

I'm installing GeoDjango on Mac OSX. I've followed the official Mac install instructions, which all went smoothly, and am now creating a spatial database template for PostGIS. However, when I try to ...
6
votes
2answers
1k views

Unions of polygons (Postgis ST_UNION for Geography type)

I am looking for a function that will return the intersection of 2 or more polygons (geography type). I am aware of ST_UNION, ST_COLLECT but it works only for geometry type. Any tip will be really ...
1
vote
1answer
859 views

psycopg2 error with QGIS 1.5

So I just installed QGIS 1.5 using the windows installer not the osgeo4w one and now any plugins that need access to PostgreSQL databases don't seem to work, they all throw a: "Couldn't import Python ...
2
votes
1answer
446 views

How to convert SHP/POSTGIS data into x, y, z, “cost” data?

Is there a way to convert a line layer (shp or PostGIS) data into (x, y , z, cost) i.e. (From_node, To_node, optional_Elevation, Cost/Weight) ?
3
votes
3answers
2k views

Writing a plugin for Qgis using python to access PostGIS and write geometries

Sorry about the strange title didn't really know how to word it. I currently use MapInfo to do most of my GIS work however I have recently installed PostGIS 1.5 and am really liking it so far. A ...
23
votes
7answers
10k views

Nearest neighbor between point layer and line layer?

I've asked this question several times on stackoverflow and irc between #qgis and #postgis and I also tried to code it or implement it my self in postgis with no real answer. Using programming (most ...
3
votes
1answer
611 views

Find polygon that contains all linestring records in PostGIS table

I'm still pretty new to this stuff, so bear with me. In PostGIS how could I find a polygon that would contain all the linestring records in a given table?
27
votes
11answers
8k views

Alternatives to pgRouting

I was wondering if there are any alternatives to pgRouting tools. Thinking about it for a bit, I think the only alternative is to use R or RPY to do the analysis. Basically I'm trying to solve ...
20
votes
4answers
4k views

Simplifying adjacent polygons

I encountered a problem simplifying set of polygons that are adjacent. If I simplify each polygon separately with the Douglas–Peucker algorithm (which is used by many open source tools), the resulting ...
11
votes
5answers
3k views

Simplifying polygons to linestring

I would like to simplify some polygons that represent rivers into linestrings. I assume that holes in polygons can be omitted. Anybody has some good idea how to simply do it? It would be nice, if it ...
31
votes
11answers
18k views

How to connect to PostGIS database from ArcMap?

How can I connect to a PostGIS database from ArcMap? Solutions for ArcGIS 9.3, 10.0 and later are acceptable. Ideally, I would like to be able to perform spatially enabled queries and receive the ...
27
votes
4answers
8k 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, ...