Questions tagged [simplify]

A type of cartographic generalization in which the important characteristics of features are determined and unwanted detail is eliminated to retain clarity on a map whose scale has been reduced.

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37 views

Simplify Slider

QGIS 3.4 appeared to have a slider for adjusting the simplification tolerance - at least that is what shows up in the 3.4 documentation, for example: https://docs.qgis.org/3.4/en/docs/training_manual/...
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36 views

Simplifying Multiple neighbouring Polygons, removing gaps and overlaps

My main goal is to simplify multiple polygons, avoiding overlaps and gaps between them. My initial approach was: Find intersections for each polygon so that I end up with an array of polygons, each ...
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106 views

Geopandas simplify results in gaps between polygons

The goal is to simplify the geometries of a shapefile containing multipolygons. However, when I use Shapely's simplify in geopandas, the result contains gaps between the polygons. I was hoping that ...
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58 views

Generalizing / simplifying multipolygon in PostGIS without missing polygons?

By following the rules from this site, I got the output but some polygons do not come within the simplified polygon. I think the problem is with topology. Is there any solution?
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1answer
61 views

“Average” of two lines

I have a dataset of pairs of parallel linear features (railway tracks) and I need to simplify each pair into its central/median line. This could be achieved by computing a skeleton as suggested in ...
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1answer
157 views

Simplify multiple lines: create central axis?

I have a layer with railway lines, downloaded from OpenStreetMap. Every single track is represented separately, so at trainstations, you have several parallel lines, as well as sidelines that lead to ...
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45 views

Convex boundary of polygon [closed]

Is there any tool that can help me with my problem? I have polygons looking like this : And what I want, is to simplify or gain convex boundary of such polygons. I tried Simplify Polygon in ArcMap, ...
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1answer
150 views

PostGIS snap line segment endpoint to closest other line segment

I have a PostGIS table of singlepart line segments that I've run the ST_ChaikinSmoothing function on. Smoothing all of the line segments worked great, but these simplified geometries created small ...
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2answers
100 views

Reduce complexity of KML file

I have a 6mb KML file I am using with the Leaflet API/Ominvore plugin. It is just a centerline of a long distance trail. What would be the best way to make it smaller? Reduce complexity etc.
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47 views

How to remove narrow 'notches' in polygons?

I am currently working on a project where i am doing a union on several feature classes. The union normally creates several polygons which share edges/borders. however after running dissolve on the ...
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1answer
129 views

Simplify a circle into square with SF

I want to obtain a square from a circle using simplification function in sf. This is my circle: With this code, I obtain a rhombus plot(st_simplify(st_geometry(sfdf),dTolerance = 1000)) How can I ...
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2answers
371 views

QGIS remove useless vertex to simplify polygon

I received a shapefile which is the result of a combination of several polygon. I want to clean and simplify it as there are many useless vertex as you can see on the picture. This is only one feature ...
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1answer
51 views

Remove small interstices on the edges of a polygone

How can I remove the white interstices on the edges (and interior) of a polygone or polyline, as represented in the first figure below? I want to get smooth and continuous edges, capturing the global ...
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1answer
594 views

Simplify geometry

Which is the best way to convert a complex multipolygon into simple and "merged" polygon? For example, the red stroked polygon (drawn by hand of course) is the simplified version of the white ...
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1answer
184 views

How to delete from mutipolygons all but the biggest polygon in QGIS

I have a bit too complex multipolygon set to be used in a web application (thematic map) so I'd like to simplify the structure by removing small islands of areas. I am not an expert on QGIS but so far ...
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1answer
142 views

Aggregating geometry features on geometry simplification using PostGIS?

PostGIS has ST_Simplify functionality which gets one multiline as input and returns one output multiline where the general shape of lines are retained while eliminating unnecessary detail. Instead of ...
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163 views

Building footprint polygon simplification / generalisation

I'm looking for implementations of polygon simplification algorithms that preserve topology and overall rectilinearity. The input data is building footprints which often have squarish protrusions and ...
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1answer
47 views

Reducing filesize for landslide susceptibility map

I have a large .tif file that I would like to reduce to under 15MB (currently 650MB). The file shows 3 zones of landslide susceptibility (see pic below). I am processing it so that I can upload it to ...
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16 views

What simplifying polygons functions f y = f(x) have ( y union x equal y ) property?

I've looked at GRASS v.generalize manual but they don't say. As far I can tell there's hermit but it's a Smoothing function.
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220 views

producing smooth iso polygons from raster surface? [closed]

The objective is to turn a raster surface (double value type) into smooth, visually appealing polygons representing iso-levels. I cannot stress enough that these must be visually attractive. Jaggedy ...
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1answer
250 views

Simplify Geometries 'NoneType' Error in QGIS

I need to simplify the geometries of a large amount of polygons, yet every time I run the Simplify Geometries tool in QGIS, I get the error message below. 'NoneType' object has no attribute 'type' ...
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68 views

How does the US Census Bureau simplify its Cartographic Boundary Shapefiles?

The US Census Cartographic Boundary Shapefiles are available in 1:500,000 and 1:5,000,000 and 1:20,000,000 resolutions. The boundaries are well-aligned and the data otherwise seemingly clean. How ...
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129 views

How to simplify line geometry and preserving topology in Oracle?

I have some polylines in an Oracle database which are topologically connected and I want to simplify these lines based on a tolerance directly in Oracle. I need something like ...
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1answer
819 views

Merging close lines?

I downloaded some road network data derived from OSM by GeoFabrik, see the initial state: Near Székesfehérvár (Hungary), parallel lines are probably trunk or motorway roads. I would like to simplify ...
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1answer
298 views

Geoserver shape simplification performance

So, while wondering about shape simplification in the eternal struggle for optimization, I find out (here on SE) that Geoserver and PostGIS can and will (by default) perform the trick on the fly (see ...
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2answers
780 views

Simplify polylines by eliminating short lines?

I have a river network, extracted from a DEM. Then I split it to shorter segments. The split adds some points (as shown in figure) too near to each other. I wonder how I should remove those small ...
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62 views

Output Error from SimpliPy in QGIS

I am trying to simplify a polygon layer of parliamentary constituencies in Kenya using SimplyPy in QGIS and appear to be getting an erroneous result. The method is working for most of the polygons ...
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1answer
5k views

Simplify polygons of sf object

How do I simplify an sf polygon without introducing gaps and slivers? With a shapefile, for example, I would use rmapshaper::ms_simplify(): library("pryr") library("rgdal") library("rmapshaper") ...
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211 views

Is it possible to simplify geometry only for polygons with certain attributes?

I have a map of electoral districts. Urban areas have more densely packed districts whose borders are more important to keep at high resolution. More rural districts have simpler geometries and have ...
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1answer
269 views

Create Strictly Simple Polygon in PostGIS/Shapely

The clipper lib has an amazing function to create a strictly simple polygon (definition below). Is it possible to do this in simple features (pref postgis or shapely)? A strictly simple polygon is a ...
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1answer
149 views

How do I remove only coastlines in marine shapefiles and be left with only polylines in the ocean?

I have numerous marine shapefiles that need to be simplified for display purposes. I need to eliminate the coastlines of land entirely and be left with just polylines in the ocean, as the Large ...
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1answer
214 views

Methods behind qgis:simplifygeometries and qgis:smoothgeometry?

I would like to know on which method (e.g. Douglas-Peucker line simplification) the modules qgis:simplifygeometries and qgis:smoothgeometry are built on. I cannot find further information on these ...
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29 views

Exact method used in simplify command within “Convert ArcGIS Raster to Polygons”

I am trying to understand the exact method used in the "simplify" command under the "Convert Raster to Polygons" in ArcGIS. The help page describes qualitatively what the command does, but does not ...
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107 views

Simplifying polygons without “trimming” them

I have a quite difficult issue: I need to simplify polygons, but without "trimming" them - no parts of polygon can be lost; furthermore, all holes in polygons should be filled (but this last is less ...
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294 views

'.Simplify' causes 'null geometry' errors (Python, OGR)

Question relates to an earlier one: Can't retrieve geometry (Python, OGR, Rtree) Im trying to simplify a dataset with 180k+ polygons and place the simplified geometries in a separate dataset. ...
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1answer
2k views

How to use OGR Simplify in Python

I am trying to simplify several polygons part of one shapefile using Python and OGR. However, I am stuck with how to use the simplify function as mentioned in the documentation: http://www.gdal.org/...
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3answers
636 views

How to break apart a complex line segment into simple line segments between all points?

Take for instance a very complex line string.. which has WKT like this LINESTRING(1 1,2 2,3 3,4 4,5 5 ...) I want to create two-point linestrings from many-point linestrings. SELECT ST_MakeLine(...
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1k views

Cleaning large Shapefile using v.clean in order to dissolve features?

I'm having real problems cleaning up and reducing the size of a Shapefile which is published by the UK's Environment Agency. It shows the extents of the LiDAR open data they publish: each polygon is ...
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1answer
156 views

qgis: generalisation & covex - how to? what plugin?

I'm looking for a way to generalize and simlify polygon to remove "internal spikes" as ilustrated below. The violet in input and green expected poligon.
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595 views

Postgis : Simplify a path using ST_Simplify

I have a table with latitude, longitude representing paths. I want to simplify the paths using Postgis ST_Simplify Here is a sample set of 89 GPS points i try to simplify : https://gist.github.com/...
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358 views

Simplifying boundaries of divisions of country using QGIS?

I am trying to create a map to show all the divisions of a country (regions, departments), but the original map (one SHP file), with a lot of detail in the boundaries, is 5-Mb sized. I'd like to ...
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2answers
721 views

Simplify a shapefile/GeoJSON polygon without “uncovering” territory?

I've been using Mapshaper to simplify some very complex polygons (boundaries of countries). The goal is to create relatively simple polygons which can be used to determine whether a given lat/lon ...
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49 views

Simplify geometry of multiple features without losing shape [duplicate]

I am simplifying administrative boundaries using a high simplify tolerance (which is my intention so as to get a minimalist appearance). However, after simplification, the borders of the regions no ...
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1answer
383 views

How to use GRASS Generalize to reduce GADM data size to 1/5 preserving topology?

The GADM is a great resource from global boundaries of countries, states and municipalities. The amount of detail is suitable for many analyses but when it comes to mapping or displaying it is often ...
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1answer
440 views

Simplify networks from OSM in qgis

I want to make something like in this question in QGIS. In ArcGIS there is available Make Divided Roads plugin. Is there easy way to make the same job in QGIS?
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1answer
3k views

Advanced Digitizing Error CAD tools are not enabled for the current map layer

Using QGIS 2.8.4. I want to use the Simplify function so turn on the Advanced Digitizing menu. The panel displays an error "CAD tools are not enabled for the current map layer" and the error message ...
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1answer
171 views

How to delete vertices with the same direction

I have feature with a big amount of vertices. But these vertices are totally useless and make Qgis editing too slow. Lets look on image with example: These vertices inside of black line I want to ...
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1k views

Algorithm to simplify a Polygon/Series of Points to a given number of Points

I have a polygon (or let's call it just a series of points). I want to simplify it (reduce the amount of points) to a given number of points. Currently I use Douglas Peucker and try to guess the ...
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0answers
289 views

Filtering Small Areas of Shapefiles Using R

I'm trying to use the method proposed by the @ialm in the Question "How to speed up the plotting of polygons in R?" There, he loads the maps using getData from the raster package, I tested and it ...
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704 views

How to calculate tolerance for TopologyPreservingSimplifier in JTS?

I am trying to simplify some areal geometries (POLYGON\MULTIPOLYGON) using JTS's TopologyPreservingSimplifier.simplify(Geometry geom, double distanceTolerance) From the JavaDoc: void ...