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1500 questions
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1 answer

Resampling to highest or lowest resolution when dealing with rasters of varying resolutions

I'm looking for recommendations on best practices for dealing with raster data layers with different resolutions and projections. The advice I've been given is to always resample to the layer with the lowest resolution before performing any…
Matt SM
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3 answers

Account for bridge overpasses in a ground DEM to allow for water flow under the overpass

I have a bare earth DEM made from lidar data (A). It works well and has passed all accuracy tests. It is used in storm surge models. The problem we are having is on underpasses. I need to allow water to flow through underpasses when one road crosses…
If you do not know- just GIS
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19
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3 answers

How to perform a true GIS clip of polygons layer using a polygon layer in R?

I would like to do a true GIS Clip in R of soils polygons using a series of single boundary polygons, but I cannot find an R function to properly do it. It should work just like the clip function in ESRI's ArcMap. I've tried the over method in sp…
user29199
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19
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4 answers

How to use consistent symbology between multiple stretched rasters in ArcMap?

I have a series of continuous rasters representing the same phenomenon over time, so I need to use the same symbology across them all. So I set the stretched symbology of the first raster, with a color ramp from the min/max values: Now in the…
Stephen Lead
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19
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6 answers

3D perspective on maps in Leaflet, CartoDB?

Are there any JS library out there that would render normal, flat maps (like Leaflet) into a perspective map like this one, on the web: Also, anyone seen anything that could turn CartoDB data into 3D representation, like this?
knutole
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19
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3 answers

Achieving four color theorem for QGIS

I recently looked at Applying four colors theorem in polygon map using ArcMap which relates to this topic but as far as I can tell there is currently not a working plugin or script for QGIS 2.0 to achieve a four color theorem for styling polygon…
clhenrick
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19
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2 answers

How to add a halo to a text in the composer?

I would like to add texts with halo, in the composer (not in the map). Do you know a way to do it? I'm using QGIS 2.0.1
cd44
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3 answers

Basic If/Then in Python Parser of ArcGIS Field Calculator?

I am using ArcGIS 10.2 for Desktop, and I've been looking through this site, and can't seem to figure out my answer yet. Very new to VBA and Python, but lots of years with ArcGIS. I know I can do this the slow way with Select By Attributes, but…
BenW
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19
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4 answers

Get all vertices of a polygon using OGR and Python

I'm having a little trouble with the Python OGR API. What I am trying to do is get all the coordinates of each vertex of the outer ring of a polygon. This is what I have so far: import osgeo.ogr import glob path = "/home/woo/maps/" out = path +…
Nathan W
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3 answers

What is the precision of SELECT DISTINCT on PostGIS geometry column?

I wonder what the precision of the SELECT DISTINCT operator is on a PostGIS geometry. On my system, the following query gives me a count of 5, which means that the inserted points are considered equal if they differ by less than 1e-5 and I am not…
yellowcap
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1 answer

What is difference between ST_DWithin and ST_Distance for proximity search in PostGIS?

I have records stored in a table with latitude/longitude coordinates stored in a geometry field. I want to find all records nearby a user supplied reference point. Note "nearby" probably means less than 100km (possibly even smaller). Most examples…
User
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19
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6 answers

How to randomly subset X% of selected points?

What methods are available in ArcGIS 10.2 to randomly subset a selection of points. For example, in the attached screenshot I am interested in keeping 20% of the selected points and deleting the rest.
Aaron
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2 answers

Accessing existing instance of QGIS in stand-alone Python script

For my own data analysis pipeline, I am running a split screen setup with IPython notebooks on one side, generating variables from source data, pushing them to a CSV file which QGIS then reads/joins to an appropriate geography, instantly visible on…
ako
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4 answers

Python literature relevant to QGIS

Python for ArcGIS is a book that I have been looking at. Does anyone know if this would be applicable in QGIS? I am not looking to write application/plugins, simply get better at understanding expression etc. for standard workflow. e.g. queries and…
LandArch
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3 answers

Releasing PyQGIS file locks

What triggers the release of file locks in pyQGIS? I am trying to delete a few data sources (used temporarily) by calling QgsVectorFileWriter.deleteShapeFile, but I have to quit QGIS before I can do that. I have loaded the sources into…
user23603
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