Any way to read bathymetry surveys (*.xyz) into QGIS as a TIN or as raw points?
Most GIS software is not really built for dealing with the amounts of data present in both raw multibeam data and raw lidar data (the two datatypes are quite similar in content and topic).
GIS software struggles when showing many points because no filtering is applied in an effort to reduce the number of individual returns shown.
All in all, you need to preprocess the data in a bit of dedicated software to reduce the point density and potentially convert it into a more suitable format, such as a raster.
The term "bathymetry" originally referred to the ocean's depth relative to sea level, although it has come to mean “submarine topography,” or the depths and shapes of underwater terrain.
In the same way that topographic maps represent the three-dimensional features (or relief) of overland terrain, bathymetric maps illustrate the land that lies underwater. Variations in sea-floor relief may be depicted by color and contour lines called depth contours or isobaths.
Bathymetry is the foundation of the science of hydrography, which measures the physical features of a water body. Hydrography includes not only bathymetry, but also the shape and features of the shoreline; the characteristics of tides, currents, and waves; and the physical and chemical properties of the water itself.
Solution 1: Import using GRASS
The r.in.xyz module 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.xyz is 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).
Source: https://grass.osgeo.org/grass73/manuals/r.in.xyz.html Also see this post for more info: Visualizing a LiDAR point cloud in 3D with GRASS?
Solution 2: LAStools
First convert the ascii xyz data into a las file (compressed, .laz), in ubuntu terminal. Then create a dem from the laz file, in this case stored as an asc raster. [Make] a hillshade (in this case geotiff) is also nice, you may do it for all the laz files in a directory.
Solution 3: Directly in QGIS
Add your xyz ascii file as a vector layer by "add delimited text layer". Then use "Interpolation" plugin to create a raster (from TIN or IDW) out of your delimited text layer (or use Raster-Analysis-Grid for more options)
Solution 4: Python and matplotlib
# -*- coding: utf-8 -*- """ __date__ 2013-11-16 __author__ josef __web__ http://hydrogeotools.blogspot.se/ To import xyz data from an ascii file, interpolate and save as geotiff """ import numpy as np import matplotlib.mlab as ml import scipy.interpolate as il #for method2, in case the matplotlib griddata method fails from osgeo import gdal from osgeo import osr fil_in = r"""/PathToFile/FileName.xyz""" #CHANGE HERE raster_ut = r"""/PathToFile/RasterOut.tif""" #CHANGE HERE x,y,z = np.loadtxt(fil_in, skiprows=1, delimiter=" ",unpack = True) #CHANGE HERE xmin,xmax,ymin,ymax = [min(x),max(x),min(y),max(y)] #size of 1 m grid nx = (int(xmax - xmin + 1))#CHANGE HERE ny = (int(ymax - ymin + 1))#CHANGE HERE # Generate a regular grid to interpolate the data. xi = np.linspace(xmin, xmax, nx) yi = np.linspace(ymin, ymax, ny) xi, yi = np.meshgrid(xi, yi) # Interpolate the values of z for all points in the rectangular grid # Method 1 - Interpolate by matplotlib delaunay triangularizatio and nearest neigh. PLEASE NOTE! THIS FAILS QUITE OFTEN (http://matplotlib.org/api/mlab_api.html#matplotlib.mlab.griddata) But there might be a solution - install mpl_toolkits.natgrid (http://matplotlib.org/mpl_toolkits/) zi = ml.griddata(x,y,z,xi,yi,interp='nn') #interpolation is 'nn' by default (natural neighbour based on delaunay triangulation) but 'linear' is faster (see http://matplotlib.1069221.n5.nabble.com/speeding-up-griddata-td20906.html) # PLEASE NOTE! Method 1 fails sometimes and then using mpl_toolkits.natgrid may be a solution (http://matplotlib.org/api/mlab_api.html#matplotlib.mlab.griddata) (http://matplotlib.org/mpl_toolkits/) # Otherwise, try Method 2 - Interpolate using scipy interpolate griddata #zi = il.griddata((x, y), z, (xi, yi),method='linear') #(may use 'nearest', 'linear' or 'cubic' - although constant problems w linear) #--------------- Write to GeoTIFF ------------------------ nrows,ncols = np.shape(zi) xres = (xmax-xmin)/float(ncols) yres = (ymax-ymin)/float(nrows) geotransform=(xmin,xres,0,ymin,0, yres) output_raster = gdal.GetDriverByName('GTiff').Create(raster_ut,ncols, nrows, 1 ,gdal.GDT_Float32,['TFW=YES', 'COMPRESS=PACKBITS']) # Open the file, see here for information about compression: https://gis.stackexchange.com/questions/1104/should-gdal-be-set-to-produce-geotiff-files-with-compression-which-algorithm-sh output_raster.SetGeoTransform(geotransform) # Specify its coordinates srs = osr.SpatialReference() # Establish its coordinate encoding srs.ImportFromEPSG(3010) # This one specifies SWEREF99 16 30 output_raster.SetProjection( srs.ExportToWkt() ) # Exports the coordinate system to the file output_raster.GetRasterBand(1).WriteArray(zi) # Writes my array to the raster