Spatial

问题 I am using gIntersection to clip a nationwide path network by polygons one at a time from a SpatialPolygonsDataFrame. I am looping through each polygon, clipping the path network, calculating the length of the clipped paths, and saving this to a dataframe called path.lgth: poly<-readShapePoly("C:\\temp\\polygons.shp") paths<-readShapeLines("C:\\temp\\paths.shp") #loop through all polygons clipping lines path.lgth<-data.frame() for (i in 1:length(poly)){ clip<-gIntersection(paths,poly[i,])

问题 I have a function which takes two arrays containing the tokens/words of two texts and gives out the cosine similarity value which shows the relationship between both texts. The function takes an array $tokensA (0=>house, 1=>bike, 2=>man) and an array $tokensB (0=>bike, 1=>house, 2=>car) and calculates the similarity which is given back as a floating point value. function cosineSimilarity($tokensA, $tokensB) { $a = $b = $c = 0; $uniqueTokensA = $uniqueTokensB = array(); $uniqueMergedTokens =

问题 I have a line shapefile containing roads, and I'd like to use it to create a network dataset. In ArcGIS, I'd do this with the Network Analyst extension (see here). Is there an R package with the equivalent functionality? I've checked out Bivand's Cran Task View for the analysis of spatial data, and I've searched a bit on SO and the GIS SE, but I haven't found any good leads. I've also looked through Bivand et al.'s (2013) Applied Spatial Data Analysis with R. I've been using R for a while,

问题 I'm trying to get around the fact that Entity Framework Core doesn't have support for Spatial Types by using the DBSet.FromSQL Method, and hand rolling a migration to add a geography column on SQL Server. Here's my DataContext public interface IDataContext { DbSet<PointOfInterest> PointsOfInterest { get; set; } int SaveChanges(); Task<int> SaveChangesAsync(CancellationToken cancellationToken); } public class DataContext : DbContext, IDataContext { public DataContext(DbContextOptions options)

问题 This question already has answers here : GIS: PostGIS/PostgreSQL vs. MySql vs. SQL Server? [closed] (5 answers) Closed 4 years ago . We're building a small-sized GIS Web application (as a school project) right now. In terms of spatial database support and capabilities, which is better? 回答1: Check it out for yourself, you know what you're looking for in your GIS-application: http://www.bostongis.com/PrinterFriendly.aspx?content_name=sqlserver2008_postgis_mysql_compare In general PostGIS is

问题 Say I have a LINESTRING defined as LINESTRING(-122.360 47.656, -122.343 47.656, -122.310 47.690, -122.310 47.670, -122.300 47.630) And I want to get a substring from POINT(-122.360 47.656) to POINT(-122.310 47.690) How can I return a substring of a LINESTRING in SQL Server 2008 Spatial? 回答1: Well, I managed to do it in a CLR user defined function. It is not quite a "substring" method per se, but I needed to subdivide a LINESTRING into multiple LINESTRINGs each of either X units in length or

问题 I'm currently trying to naivly get the k-nearest neighbors of a set of points, given a value k, a coordinate to use as center and a radius serving as the max distance to find points within. I'm using geographical points (SRID 4326) on a MSSQL 2008 database. The neighbors are naivly found ordering the query by the distance to the point and limiting the result. My trouble starts at limiting the points by the given radius. The distances returned by the Distance function are much larger than

问题 I have a NetCDF file of a probability surface. It's a 30x30 grid of 0.25 degree lat/lon intervals with a probability surface described in the z dimension. I can easily import this into Panoply, a NetCDF viewer: And it's then a breeze (checking one box) to interpolate/smooth the raw data to a finer grid size: However, I don't just want to visualize the data, I want to plot it in R along with bathymetry and point data. That all is no problem, but I have not found a straightforward way to

问题 I want to use the over() function from the sp package in R . I assigne a CRS . #say that polygon is EPSG3857 (Web Mercator PROJECTION) proj4string(finalPolygon) <- CRS("+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs") and all seems good. str(finalPolygon) > ..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slot > .. .. ..@ projargs: chr "+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1

问题 I need to get the cell numbers within a distance (e.g., 10 km) of one point using R, but I didn't figure out how to handle it for the raster data. library(raster) r <- raster(ncols=10, nrows=10) cellFromXY(r, c(2,2)) # get the cell number of one point How to get the cell numbers within a distance of one point? 回答1: Use extract with the buffer option and cellnumbers=TRUE r <- raster(ncols=100, nrows=100) r[]<-runif(ncell(r)) xy <- cbind(-50, seq(-80, 80, by=20)) extract(r, xy[1:3,], buffer