A mathematical procedure used to solve problems with a series of steps. Algorithms are usually encoded as a sequence of computer commands.

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24 views

What steps does SAGA GIS take when calculating Topographic Wetness, specifically when handling depression filled (by ArcMap) DEM

I am a grad student involved with hydrological modeling. In the model I work on, we are calculating the Topographic Index (TI; without transmissivity - or set to 1) using Quinn's MFD algorithm. We do ...
0
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1answer
46 views

Looking for a simple hatching algorithm

If I have an arbitrary polygon, and wish to hatch it with lines at a given angle and spacing, is there a simple low-level algorithm which will return the set of hatch lines inside the polygon?
3
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2answers
131 views

What's wrong with my IDW interpolation function (Python)?

Original Question Can anyone see what's wrong with my custom IDW interpolation below? I know there are existing libraries that can do this for me, but for various reasons including educational and ...
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0answers
26 views

How to Calculate Geolocation Intersection of Two Vectors?

I'm unfamiliar with much GIS terminology but am tasked with solving a specific geolocation problem. For what it is worth, this is for an iOS project, so the data I can collect for analysis is that ...
5
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1answer
91 views

Calculating Topographic Wetness Index (choosing from different algorithms)

Topographic Wetness Index can be expressed as Ln(a/tanB) based on the idea of Beven and Kirkby (1979) where a is the spesific catchment area (a=A/L, catchment area (A)divided by contour ...
3
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3answers
436 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 ...
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1answer
51 views

Set point NOT IN CENTER of polygon

I have a free shaped polygon. Now I draw a smaller polygon inside with a same form i.e buffer zone with negative width. Then put a point with in my buffer zone center. Its looks like this: OK. But ...
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35 views

Algorithm to find coordinates at selected intervals along a polyline?

I am developing an algorithm to search down a river at selected intervals and return the coordinates. See below: def Downstream(start, interval, data, offset=0, out=None): if out is None: ...
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0answers
17 views

return to newline arcgis/arcSDE/postgres labeling

i have two tables : parcel and owners with many to many relation ship so i want to print owners name in my parcels (type polygon), so i coded using .net a function that create field in parcel ...
0
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1answer
55 views

Algorithm to move polygon nodes when simplifying

I want to simplify polygons that come from a raster analysis. In order to avoid overlap and gaps, I first convert my polygons to lines. The problem is that all algorithm are then keeping the two end ...
4
votes
2answers
175 views

how to convert UTM northing and longitude to latitude

I am doing some work with the Military Grid Reference System (MGRS), which is based on Universal Transverse Mercator (UTM). I find that I need to convert from UTM northing and longitude (actually, ...
0
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2answers
36 views

How to maintain many-to-many relationship between feature class and table with multiple disconnected editors?

I have an application coded with VB.NET (ArcGIS Engine) and its functionality is: digitize a parcel and enter information for its owners, so i have a M-N relationship between them. every parcel has ...
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1answer
47 views

Looking for dissolve algorithm for Javascript

I have three adjacent polygons that together make up a larger shape. I need an algorithm that will dissolve the internal borders leaving only the outside border. An example would be a group of ...
0
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3answers
68 views

splitting a lines layer using points

I'm looking to accomplish a similar task to this thread: How to split a line at point positions? Using QGIS and the Processing and GRASS toolboxes available, I'm looking to split a vector layer ...
2
votes
1answer
119 views

What is the process to calculate Helmert parameters?

I have some double points (the same points in 2 different datums). I'd like to calculate the Helmert parameters but I don't understand how. NOTE: I don't need software. I need an algorithm in order ...
5
votes
1answer
126 views

ArcMap Natural Breaks Classification

I realize that ESRI is calling their implementation of Fisher-Jenks proprietary. Given the performance with mid-sized datasets, either a significant optimization or a sampling method are being ...
0
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1answer
45 views

Longest common prefix of geohashed points

I currently use Geohash to index some points and retrieve information faster by providing a geohash prefix for a given point for a given distance.. For example if I get a given point at '1600 ...
1
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0answers
31 views

What are problems & biases stemming from mathematics behind using Monte Carlo Markov Chain to make heatmap?

My buddy and I are using Monte Carlo Markov Chains to make a heat map - in the interest of rigour, and out of curiosity: "What are the problems & biases that stem from the mathematics behind ...
7
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4answers
321 views

Splitting Linestrings on the dateline with OpenLayers

A couple of years ago I posted a questions titled "The International Date Line wrap around" @jdeolive suggested I split the features at the dateLine. So I tried. So when I try to split my satellite ...
2
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0answers
34 views

What graph traversal algorithm should I use?

I would like to write an algorithm which can traverse a graph and hopefully later I can implement it to use for an indoor navigation system. The graph would come from floor plans of a building and the ...
1
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1answer
58 views

Delete duplicate spatial point/points in mssql from a perticular location

I am working with a Spatial data which has a street intersection points.... I get the intersection points from spatial query on street/roads datain MMSQL . but in my case some streets/roads are multi ...
2
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0answers
43 views

how to assign unique attribute value per neighborhood? [duplicate]

I have a feature class of adjacent polygons and I want to assign an integer attribute value to my polygons based on the following rules : a polygon must not have the same attribute value than any of ...
3
votes
1answer
106 views

Is there a method in SQL Server (2008 or 2012) that will return the equivalent of the Esri LabelPoint for geometry?

I'm looking for a method that is equivalent to the Esri LabelPoint for SQL Server Geometry (or fairly close). Does it exist by a different name? Or is there an after-market implementation? I found ...
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0answers
60 views

Line defined by two geographical points crossing circle area with defined radius

I'm trying to calculate the amount of lines defined by two geographical points crossing a circle area defined by a center and radius. I've tried to use algorithm discussed here, but in my case it ...
0
votes
1answer
146 views

How can I always run an algorithm with standard input shapefiles from mapcanvas in QGIS 2.0.1?

I created a model in the graphical modeler and I want to run that model always with two specific polygon shapefiles from my project, e.g. pst and astenot. Whenever I run my model, it asks me to set ...
1
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1answer
34 views

When was MFD renamed to FD8?

According to my understanding, the Multiple Flow Direction (MFD) algorithm was originally defined in The Prediction of Hillslope Flow Paths for Distributed Hydrological Modelling using Digital Terrain ...
0
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1answer
53 views

Divide a Square to a serval equal squares using Acrgis [closed]

hi i'm looking for an algorithm to split a square to a SEVERAL equal squares: i have only : x min , y min x max , y max please see picture (not valid picture only to describe problem): any ...
0
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2answers
161 views

Spatial databases in location based search

I'm developing a location based application in which i was in the plan of dividing the globe into grids and when the client requests information, will create a table or similar data model which will ...
7
votes
2answers
255 views

Lossless Polygon Simplification?

Is there a standard/recommended algorithm for simplifying a polygon without shrinking any of its original boundaries? Right now I'm using TopologyPreservingSimplifer within JTS and running into ...
3
votes
1answer
56 views

Exploratory search for clusters in point data

This is a more conceptual than practical question and is about exploratory cluster identification. While there are very specific meanings in the geography canon as to what they are, in economics they ...
1
vote
4answers
414 views

How can I Destripe Landsat Images?

I am working with Landsat 7 ETM+ SRC-off imagery. I'm doing some land-cover classification for a place in Kenya. My problem is the no-data stripes in the image. Is there a way in which I can ...
4
votes
2answers
88 views

Good algorithm to detect “wrong” features in a vectorial coverage

I am working with a bunch of shapefiles. Each shapefile consisting in rectangles with an integer attribute representing the strength of a signal. I serve these vector files as overlays on a base map, ...
4
votes
3answers
182 views

How to number polygons according to their spatial relationships?

I have, for example, this layer in postgresql (polygons): table : poly (objectid: integer, num: integer, shape: geometry) I want to enumerate the polygons from left to right and top to bottom ...
3
votes
2answers
239 views

Similarity between two raster maps

Having two raster maps as the examples below: We are interested in evaluating their similarities. As shown, they are not fully overlapping. We guess one way is to clip small one area from the ...
2
votes
2answers
96 views

Finding a route with desired cost not minimum cost

The goal of routing is usually finding the route with minimum cost. That cost can be distance, time, calories or some other value but still our desire is to find the route that costs least. But what ...
2
votes
0answers
83 views

Find and destroy duplicate OSM multipolygon/polygons in TileMill/PostGIS

In OpenStreetMap there are sometimes multipolygons where attributes are present on both the polygon and the multipolygon relation, such as the Grampians National Park: ...
2
votes
1answer
129 views

How to discretise a line into grid lines

Having a line and a grid, the aim is to discretise the line into grid lines. In the following figure, the given line is in black, its intersections with grid lines are blue, the desired is set of ...
0
votes
0answers
60 views

Route through water polygons

I have a water-polygon grid shape file as shown (Each grid is 1latx1long): I have created this in QGIS and files (coastal lines and land polygons) selected from http://openstreetmapdata.com/data ...
3
votes
2answers
89 views

Breaking a range of values into buckets for a gradient

If I have a range of values and want to make a choropleth map with a gradient, what algorithms are out there to determine the value ranges for the different colors in the gradient? For example, if I ...
0
votes
2answers
314 views

Detecting invalid polygons (self-intersecting or touching)

An invalid polygon can be defined as one that intersects itself, or one where the lines make contact, ie, the two shapes at the top of this picture. Given the XYPoints of a polygon, what logic ...
3
votes
1answer
190 views

How is slope of a surface in an arbitrary direction produced?

I am currently developing a program that requires that I calculate the slope for each cell in a DEM. However when I try to understand the algorithm to be used I get stuck trying to understand exactly ...
4
votes
2answers
216 views

What is the algorithm used by ESRI for finding loops in a geometric network?

I've been trying to develop some code for ArcMap (VB .net) that would take a river network, identify and label the loops. These loops can be simple bifurcations or highly thread braided channels. I ...
0
votes
1answer
707 views

NED (LTP) to ECEF Orientation Conversion (Tait Bryan Angles)

I have an application where I need to convert an orientation from NED - given a WGS84 latitude and longitude - to ECEF. I have yaw, pitch and roll as Tait Bryan angles (XYZ) relative to the local ...
3
votes
5answers
348 views

How can I count overlapping polygons, resulting in a new set of polygons?

I have 100 polygons in a GeoJSON file that partially overlap each other. I would like to produce 100 new polygons as follows: The area covered by any of the original 100. This is their union. The ...
1
vote
2answers
92 views

Frequency of partially or fully overlapping lines

Let L be a set of line-segments (lines) in a two-dimensional (2D) Euclidean space that are randomly (say, using uniform random function) distributed, that is, some may overlap other(s). Overlapping ...
2
votes
1answer
126 views

Center point approximation of a polygon

I would like to get a center point approximation of a set of polygons so I can do a NN lookup to use for assignment instead of a point in polygon query. Lets say I have this set of polygons: I ...
4
votes
1answer
109 views

Which spatial bundling or grouping algorithm optimally groups elements by attribute?

As I delve deeper into GIS, I find myself trying to improve efficiencies of certain procedures and processes. The one process I'm working on now is spatially scheduling construction projects. For ...
2
votes
0answers
142 views

Iteration based positioning on Matlab - retrieving coordinates between iterations

This is my first question on SE so let me know if I'm not asking my question in the right place. So basically, I have an algorithm which uses UMTS measurement events for positioning estimation, which ...
3
votes
1answer
84 views

Placename matching algorithms and services for geocoding

Are there any placename-specific matching algorithms, routines or services available? By placename specific I mean not just a simple string-difference match, or soundex/metaphone, but something that ...
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votes
1answer
75 views

How to find the most east or west longitude around the date line

I've got a python script that is comparing extents of rasters in various projections. Generally it works, but sometimes, especially when the rasters are global in extent or cross the dateline it ...