Tag Info

Hot answers tagged

11

create a new field and copy the first two digits from the left using the field calculator -> for text, you can use (left(fieldname,2)) in the field calculator. With numeric field you can use floor(fieldname/1000) dissolve your polygons based on this new field -> this command is in vector -> geometry -> dissolve


3

You could try to use OpenStreetMap data. Global land and water polygons are freely available from http://openstreetmapdata.com/data/land-polygons, a service offered by Jochen Topf. In contrast to the above mentioned Natural Earth dataset OpenStreetMap data is much more detailed and therefore requires more disk space.


3

I take no credit for the following Python snippet, which is taken from an ESRI idea found by Googling 'convert from julian to calendar date arcgis'. As trivia, they mention the data they were working with came from the FAA. There is also mention of data coming over from Excel in that format despite being entered differently. I apologize if my cut/paste ...


2

There is the "Rectangles ovals digitizing” plugin in the official QGIS repository. To activate the tools in the tool bar you have to first select a vector layer containing polygon or multipolygon features. After that start editing on this layer. Of course, it doesn't work for vector layers containing point or linestring features.


2

You might like to have a look at this document, which shows an example of using the Polygonizer to make a geological map. http://confound.me.uk/maps/ppv4.pdf‎ After some recent problems, in my version of QGIS (2.3.0-Master, from Ubuntugis) the Polygonizer is now working again. Search for 'Polygonize' in the Processing Toolbox. N.


2

Here is the data for Australia straight from their government's website: http://data.daff.gov.au/anrdl/metadata_files/pa_nsaasr9nnd_02211a04.xml Here is the data for New Zealand from their government's data portal: http://www.stats.govt.nz/browse_for_stats/people_and_communities/Geographic-areas/digital-boundary-files.aspx From here you can merge the two ...


1

Found a link which contained solutions to adding 2 layers or more: http://stackoverflow.com/questions/1769648/addition-with-null-values Basic gist is when using 2 columns: coalesce("Column_1"+"Column_2","Column_1","Column_2") Using 3 columns or more, I used: coalesce("Column_1",0.00) + coalesce("Column_2",0.00) + coalesce("Column_3",0.00) + ....... ...


1

The difference is only due to the symbology, your original raster is symbolized with a classified method and bilinear interpolation resampling. I don't know what's used to symbolize the second one, maybe just pixel values or classified with nearest neighbor resampling. You can manage this in ArcGIS using the Symbology and Display tabs of the layer ...


1

The shapefile format has some limitations due to the underlying dbase database format. See: http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=Geoprocessing%20considerations%20for%20shapefile%20output In your case, the limit of 10 characters field name and 255 fields total is hit. Try some other format, like spatialite. Or think about ...


1

You can snap a line to itself, but only after saving. My workaround is to digitize the line, but set the last point a bit offset to the first point, then save, and then move the last point to the first. As a consequnce, I start digitizing a new closed line with a point that is already created by another adjacent polygon if possible.


1

These are the steps I followed to install Qgis 1.8 from source in my $HOME/qgis18 directory: Prerequisites: ccmake installed from synamptic; gdal,proj4,geos,etc. installed from Ubuntugis repository; Procedure: Download datasource from here $mkdir -p ${HOME}/qgis18 $cd qgis18 $mkdir build $cd build $ccmake .. (configure all paths and dependences) $make ...


1

I am just playing around with this. I found the same site/formula that @Alex Tereshenkov mentioned in the comment above . Here is what my field calculator expression and codeblock look like: def CalcDate(JD): L= JD+68569 N= 4 * L /146097 L= L - (146097*N+3)/4 I= 4000*(L+1)/1461001 L= L-1461*I/4+31 J= 80*L/2447 K= L-2447*J/80 L= J/11 J= ...


1

Here is an attempt to do this in R. I use gIntersect and compare the layer with itself. Every polygon intersects with itself, so I then use the row sums to determine if there is only one intersect and select those. library (rgeos) library(sp) # make some polys data (meuse) coordinates(meuse) <- ~x+y polys <- gBuffer(meuse, width=70, byid=T) ...


1

You may use v.select in GRASS GIS with "operator=disjoint" - features do not spatially intersect. Note that it requires GRASS GIS been compiled with GEOS support. Just check if "disjoint" is a supported parameter in v.select. Edit: in case of one map only, check v.to.db and its parameter "sides". It extracts categories of areas on the left and right side of ...


1

Yes: 1) The proposed solution (Using processing algorithms from the console) import processing # find the algorithm processing.alglist("Multipart to singleparts") Multipart to singleparts----------------------------->qgis:multiparttosingleparts # help processing.alghelp("qgis:multiparttosingleparts") ALGORITHM: Multipart to singleparts ...


1

For GRASS you can use the r.colors to modify the color table for a raster map. r.colors also ships with pre-defined color maps for temperature scales. It's simple to use even r.colors map=spring color=celsius You can also copy the color table from one map to another r.colors map=spring2 raster=spring For more details see the GRASS GIS manual ...


1

This is a really good feature idea - thanks for the inspiration. I've just added this ability to QGIS. So if you run a current snapshot, or when 2.4 is released, there's an easy way to set a filter for an attribute table:



Only top voted, non community-wiki answers of a minimum length are eligible