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## man page of r.in.xyz

### r.in.xyz: Create a raster map from an assemblage of many coordinates using univariate statistics.

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## NAME

r.in.xyz- Create a raster map from an assemblage of many coordinates using univariate statistics.## KEYWORDS

raster, import, LIDAR## SYNOPSIS

r.in.xyz r.in.xyz help r.in.xyz[-sgi]input=name output=name[method=string] [type=string] [fs=character] [x=integer] [y=integer] [z=integer] [zrange=min,max] [zscale=float] [percent=integer] [pth=integer] [trim=float] [--overwrite] [--verbose] [--quiet]Flags: -sScan data file for extent then exit-gIn scan mode, print using shell script style-iIgnore broken lines--overwriteAllow output files to overwrite existing files--verboseVerbose module output--quietQuiet module outputParameters: input=nameASCII file containing input data (or "-" to read from stdin)output=nameName for output raster mapmethod=stringStatistic to use for raster values Options:n,min,max,range,sum,mean,stddev,variance,coeff_var,median,percentile,skewness,trimmeanDefault:mean type=stringStorage type for resultant raster map Options:CELL,FCELL,DCELLDefault:FCELL fs=characterField separator Default:| x=integerColumn number of x coordinates in input file (first column is 1) Default:1 y=integerColumn number of y coordinates in input file Default:2 z=integerColumn number of data values in input file Default:3 zrange=min,maxFilter range for z data (min,max)zscale=floatScale to apply to z data Default:1.0 percent=integerPercent of map to keep in memory Options:1-100Default:100 pth=integerpth percentile of the values Options:1-100 trim=floatDiscard percent of the smallest and percent of the largest observations Options:0-50## DESCRIPTION

Ther.in.xyzmodule will load and bin ungridded x,y,z ASCII data into a new raster map. The user may choose from a variety of statistical methods in creating the new raster. Gridded data provided as a stream of x,y,z points may also be imported.r.in.xyzis designed for processing massive point cloud datasets, for example raw LIDAR or sidescan sonar swath data. It has been tested with datasets as large as tens of billion of points (705GB in a single file). Available statistics for populating the raster are: |n| number of points in cell |min| minimum value of points in cell |max| maximum value of points in cell |range| range of points in cell |sum| sum of points in cell |mean| average value of points in cell |stddev| standard deviation of points in cell |variance| variance of points in cell |coeff_var| coefficient of variance of points in cell |median| median value of points in cell |percentile| pthpercentile of points in cell |skewness| skewness of points in cell |trimmean| trimmed mean of points in cellVarianceand derivatives use the biased estimator (n). [subject to change]Coefficient of varianceis given in percentage and defined as (stddev/mean)*100.## NOTES

Gridded dataIf data is known to be on a regular gridr.in.xyzcan reconstruct the map perfectly as long as some care is taken to set up the region correctly and that the data's native map projection is used. A typical method would involve determining the grid resolution either by examining the data's associated documentation or by studying the text file. Next scan the data withr.in.xyz's-s(or-g) flag to find the input data's bounds. GRASS uses the cell-center raster convention where data points fall within the center of a cell, as opposed to the grid- node convention. Therefore you will need to grow the region out by half a cell in all directions beyond what the scan found in the file. After the region bounds and resolution are set correctly withg.region, runr.in.xyzusing thenmethod and verify that n=1 at all places.r.univarcan help. Once you are confident that the region exactly matches the data proceed to runr.in.xyzusing one of themean, min, max, ormedianmethods. With n=1 throughout, the result should be identical regardless of which of those methods are used.Memory useWhile theinputfile can be arbitrarily large,r.in.xyzwill use a large amount of system memory for large raster regions (10000x10000). If the module refuses to start complaining that there isn't enough memory, use thepercentparameter to run the module in several passes. In addition using a less precise map format (CELL [integer] or FCELL [floating point]) will use less memory than a DCELL [double precision floating point]outputmap. Methods such asn, min, max, sumwill also use less memory, whilestddev, variance, and coeff_varwill use more. The aggregate functionsmedian, percentile, skewnessandtrimmed meanwill use even more memory and may not be appropriate for use with arbitrarily large input files. The default maptype=FCELL is intended as compromise between preserving data precision and limiting system resource consumption. If reading data from a stdin stream, the program can only run using a single pass.Setting region bounds and resolutionYou can use the-sscan flag to find the extent of the input data (and thus point density) before performing the full import. Useg.regionto adjust the region bounds to match. The-gshell style flag prints the extent suitable as parameters forg.region. A suitable resolution can be found by dividing the number of input points by the area covered. e.g. wc -l inputfile.txt g.region -p # points_per_cell = n_points / (rows * cols) g.region -e # UTM location: # points_per_sq_m = n_points / (ns_extent * ew_extent) # Lat/Lon location: # points_per_sq_m = n_points / (ns_extent * ew_extent*cos(lat) * (1852*60)^2) If you only intend to interpolate the data withr.to.vectandv.surf.rst, then there is little point to setting the region resolution so fine that you only catch one data point per cell -- you might as well use "v.in.ascii -zbt" directly.FilteringPoints falling outside the current region will be skipped. This includes points fallingexactlyon the southern region bound. (to capture those adjust the region with "g.region s=s-0.000001"; seeg.region) Blank lines and comment lines starting with the hash symbol (#) will be skipped. Thezrangeparameter may be used for filtering the input data by vertical extent. Example uses might include preparing multiple raster sections to be combined into a 3D raster array withr.to.rast3, or for filtering outliers on relatively flat terrain. In varied terrain the user may find thatminmaps make for a good noise filter as most LIDAR noise is from premature hits. Theminmap may also be useful to find the underlying topography in a forested or urban environment if the cells are over sampled. The user can use a combination ofr.in.xyz outputmaps to create custom filters. e.g. user.mapcalcto create a mean-(2*stddev) map. [In this example the user may want to include a lower bound filter inr.mapcalcto remove highly variable points (smalln) or runr.neighborsto smooth the stddev map before further use.]ReprojectionIf the raster map is to be reprojected, it may be more appropriate to reproject the input points withm.projorcs2csbefore runningr.in.xyz.Interpolation into a DEMThe vector engine's topographic abilities introduce a finite memory overhead per vector point which will typically limit a vector map to approximately 3 million points (~ 1750^2 cells). If you want more, use ther.to.vect -bflag to skip building topology. Without topology, however, all you'll be able to do with the vector map is display withd.vectand interpolate withv.surf.rst. Runr.univaron your raster map to check the number of non-NULL cells and adjust bounds and/or resolution as needed before proceeding. Typical commands to create a DEM using a regularized spline fit: r.univar lidar_min r.to.vect -z feature=point in=lidar_min out=lidar_min_pt v.surf.rst layer=0 in=lidar_min_pt elev=lidar_min.rstEXAMPLE

Import the Jockey's Ridge, NC, LIDAR dataset, and process into a clean DEM: # scan and set region bounds r.in.xyz -s fs=, in=lidaratm2.txt out=test g.region n=35.969493 s=35.949693 e=-75.620999 w=-75.639999 g.region res=0:00:00.075 -a # create "n" map containing count of points per cell for checking density r.in.xyz in=lidaratm2.txt out=lidar_n fs=, method=n zrange=-2,50 # check point density [rho = n_sum / (rows*cols)] r.univar lidar_n | grep sum # create "min" map (elevation filtered for premature hits) r.in.xyz in=lidaratm2.txt out=lidar_min fs=, method=min zrange=-2,50 # zoom to area of interest g.region n=35:57:56.25N s=35:57:13.575N w=75:38:23.7W e=75:37:15.675W # check number of non-null cells (try and keep under a few million) r.univar lidar_min | grep '^n:' # convert to points r.to.vect -z feature=point in=lidar_min out=lidar_min_pt # interpolate using a regularized spline fit v.surf.rst layer=0 in=lidar_min_pt elev=lidar_min.rst # set color scale to something interesting r.colors lidar_min.rst rule=bcyr -n -e # prepare a 1:1:1 scaled version for NVIZ visualization (for lat/lon input) r.mapcalc "lidar_min.rst_scaled = lidar_min.rst / (1852*60)" r.colors lidar_min.rst_scaled rule=bcyr -n -e## TODO

Support for multiple map output from a single run. method=string[,string,...] output=name[,name,...]## BUGS

nmap sum can be ever-so-slightly more than 'wc -l' with e.g. percent=10 or less. Cause unknown.nmap percent=100 and percent=xx maps differ slightly (point will fall above/below the segmentation line) Investigate with "r.mapcalc diff=bin_n.100 - bin_n.33" etc. Cause unknown. "nan" can leak intocoeff_varmaps. Cause unknown. Possible work-around: "r.null setnull=nan" If you encounter any problems (or solutions!) please contact the GRASS Development Team.## SEE ALSO

g.region m.proj r.fillnulls r.in.ascii r.mapcalc r.neighbors r.out.xyz r.to.rast3 r.to.vect r.univar v.in.ascii v.surf.rst v.lidar.correction, v.lidar.edgedetection, v.lidar.growing, v.outlier, v.surf.bspline pv- The UNIX pipe viewer utility## AUTHORS

Hamish Bowman Department of Marine Science University of Otago New Zealand Extended by Volker Wichmann to support the aggregate functions median, percentile, skewness and trimmed mean. Last changed: $Date: 2011-04-08 00:10:37 +0200 (Fri, 08 Apr 2011) $ Full index (C) 2003-2010 GRASS Development Team R.IN.XYZ(1)

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