Tagged Questions

(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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2
votes
1answer
111 views

Outward buffering

I get the ConvexHull of a set of polygons using ST_UNION and ST_CONVEXHULL functions using PostGIS. I want to know how to create an outward buffer of the created convexhull in PostGIS?
4
votes
5answers
6k views

Calculate midpoint from a series of latitude and longitude coordinates

I've got a series of longitude and latitude coordinates which represent a building outline e.g. -0.5485381346101759,53.2285150736142 -0.5482220594232723,53.22842450827133 ...
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?? ...
9
votes
3answers
372 views

Invalid geometry zoo

Many a time and oft I've spent hours struggling with bizarre bugs resulting from invalid geometries. The symptoms vary greatly, including: Database slowdowns Incorrect\Null query results Log files ...
4
votes
1answer
334 views

Sort by geometry using INHERITS?

hope everyone's doing well. I have a statewide point data set (parent table: 600K rows, 500 columns) I need to analyze at multiple scales based on several different spatial divisions. I'll also need ...
6
votes
3answers
513 views

How could I compare polygons with appropriate circle?

My problem is that I have a polygon shape file with 1034 records which are the Greek municipalities. My goal is to compare the shape of every record with the circle. In other words, I want to observe ...
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) ...
13
votes
5answers
523 views

Terminology: Polygon or Area?

When writing about GIS geometry I'm unsure whether to use the term "polygon" or "area". In particular, does the word "polygon" suggest a specific type of geometry? For example, a colleague suggested ...
9
votes
4answers
273 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, ...
19
votes
3answers
5k views

How to store lines and polygons in JSON documents?

Looking at the increasing NoSQL movement and considering that databases like MongoDB offers a new perspective in flexible data storage for GIS. What is the best way to store lines and polygons in ...
5
votes
1answer
295 views

Which projection casts rays from a point on the surface of the globe to a cylinder?

What is the name of a map projection that casts rays from a point on the surface of the globe to a cylinder? Some people who make sundials put a map of Earth on the sundial. I want to use the "right" ...
5
votes
2answers
294 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 ...
10
votes
2answers
5k views

Using python in ArcGIS, create a line of varying distance from an origin point

What I'm trying to do is create a line feature from a single point, using a set distance and angle. Using ArcGIS and Python (I hope). Here's the scenario: Say I have a point at these coordinates: ...
34
votes
4answers
6k 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 ...
3
votes
4answers
709 views

Update geometry(polygon) of shape file based on a point layer

I have two shape files. Polygon shape file Point file contains some points. Now i want to delete all the vertex of polygon shape file which are available in point file. I am using ...
11
votes
4answers
397 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 ...
9
votes
2answers
4k views

Cutting up a shape file into smaller parts

I've downloaded the 350MB coastline shape file from Openstreetmap, but I really would like to work with a small part of them, is there a way to generate a shapefile of a small area. I'm using MacOSX ...
4
votes
3answers
1k views

Is the Fourth Dimension used in GIS?

Whilst working with OGR, I came across the following field used define a geographic dataset: COORD_DIMENSION The spatial dimension (2, 3 or 4 dimensional) of the column. Whilst I've used 2D and 3D ...
4
votes
2answers
1k views

create temporary point geometry feature from coordinates in OGR with Python

I have two shapefiles containing two types of geometry features: one contains polygons and the other linestrings. Because I'd like to use the Within method to check whether the end(or start) of a ...
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
640 views

Way to Ensure that the Image Centroid is Within Image Bounds

My application uses the ArcGIS Silverlight API to select polygons from a map layer. It uses the Geometry.Extent.GetCenter() method to get the centroid of the shape and add a thumbtack image at those ...
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 ...
2
votes
3answers
681 views

How do i find out geometries for areas?

I was wondering if anyone could help me out with a website which I can use to get geometries for a area. What I'm looking for is something like google maps where I can drag a cursor over a area of the ...
3
votes
1answer
494 views

postgres command to save the line coordinates in openlayers

I am working on project that we create one map ant editing toolbar. Then by using that editing tool bar we can draw point, line, polygon on the map. Next we are converting the line, point, polygon ...
1
vote
0answers
271 views

Export topology tables to txt files using ArcObjects, generating directed graph, and finding intersections

I want to export topology tables to text files: for points: 1 id x y for lines: line id fompoint.x from point.y topoint.x topoint.y for polygons: id line id 1, line id 2... 2 arc ...
9
votes
1answer
418 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
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 ...
0
votes
2answers
155 views

modeling of spatial objects

I have a line and polygon in this image. If i find the intersection of line exterior and polygon boundry, what will be the graphical representation of both objects intersection.. its my concept.. ...
6
votes
3answers
804 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
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 ...
-4
votes
1answer
138 views

vector with epsilon [closed]

if there are two points p1 and p2.and vector of both is ab .. now if i say -1 < ab < 1 condition true than return F.. is that mean by points p1 and p2 intersect to each other...?
2
votes
2answers
133 views

MMP of geometries

MBR is used for extent of geometries.. then what is the use of MMP.. is it for visualization the objects?
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 ...
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 ...
3
votes
1answer
542 views

Is it possible to figure out which “Path”(PointCollection) is clicked on within a PolyLine?

I am using ArcGIS WPF's Polyline to plot several lines (PointCollections). Adding a Path(PointCollection) looks something like this. PointCollection collection = new PointCollection(); PolyLine ...
12
votes
5answers
771 views

Simulating the expansion of polygon features

I've got what I'm hoping will be an interesting question. I'm working on an assignment for an intro to GIS course that uses some Gulf oil spill data to introduce common vector-based spatial analysis ...
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 ...
4
votes
1answer
919 views

Clipping a SqlGeometry

I have been messing around with the SqlGeometry in the Microsoft.SqlServer.Types namespace in .NET, and have been rather impressed. Can anyone provide me with an example of how I could clip a ...
10
votes
2answers
374 views

Tools for importing historical maps into modern GIS systems

What tools exist to derive geometries for use with modern GIS systems from older scanned maps? I am referring more to libraries that generate actual data rather than present an interface for manually ...
6
votes
1answer
610 views

Help simplifying multipolygons in geodjango

I have a few multipolygons that have several hundred points in them. I'm looking to create less complex "thumbnails" polygons. Naturally I'm attempting to use the simplify method, which is supposed ...
64
votes
15answers
20k 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 ...
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 ...
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: ...
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 ...
3
votes
3answers
869 views

Open .NET implementation of the OGC Geometry Object Model from Simple Feature Access 1 specification?

I am looking for a .NET implementation of the geometry object model described in OGS's Simple Feature Access, Part 1 specification. Preferably lightweight. I don't need WKT support, just the ...