10

One alternative is spline interpolation as suggested in the related post: Interpolation of multibeam bathymetry. From QGIS, use the GRASS tool v.surf.rst: Performs surface interpolation from vector points map by splines. Then, you can test different types of parameterization available within the tool. There is an option to apply a leave-one-out cross ...


10

I don't know if this is the easiest way, but one way would be to use gdal_calc.py from GDAL: gdal_calc.py -A positive_values.tif --outfile=negative_values.tif --calc="A*(-1.0)"


7

This is likely not entirely an issue with the interpolation model. Bathymetric data can exhibit considerable noise. Because of an equal weight associated with each TIN facet and outlier effect, A TIN base interpolation can extenuate this noise and is not recommended. I would apply a Topogrid (Topo to raster tool) Spline interpolation and then apply a ...


6

You could take the resulting raster from your initial conversion and use Spatial Analyst --> Math --> Times to multiply the raster by -1.


6

It depends in the method in which the DTM/DSM were derived, and what data they are based on. LiDAR, which is often used today, sometimes cannot penetrate water, therefore, datasets based on LiDAR typically do not contains bathymetry. There may be some hybrid products available where the above water surfaces are LiDAR derived, while the under water surfaces ...


5

Upon requesting "topography" for longitudes between -30 and -24 degrees and latitudes between 54 and 60 degrees, I noticed the file contained three columns, for longitude, latitude, and elevation, apparently in an XYZ ASCII output arrangement (totaling 239,704 lines). After the page was saved in ASCII text format, it could be read and processed in R: x <...


5

If your bathymetric data are current in the form of survey points then you should interpolate them onto a raster grid of the same resolution and extent as your LiDAR data. There are several methods for interpolating these points available in ArcGIS such as splining, IDW and kriging. The most appropriate method to use will depend on your data characteristics (...


5

You can use SRTM30 PLUS which include topography and bathymetry of roughly 1km spatial resolution. The data covers the entire globe. You can choose the location you want. Also, the above link has multiple versions, please check the one you need, and there is an FTP link to download the data.


5

@Rich Signell provides an excellent solution (+1). I only add this answer as an alternative depending on what you are familiar with. In QGIS you could use the Raster calculator and do this via the GUI: "myDTM@1" * -1 This is effectively the same thing as Rich's solution given that QGIS uses GDAL under the hood, but you might prefer to use a GUI instead ...


4

CleanTopo2 looks promising, and is public domain. CleanTOPO2 is a touched up and generalized version of SRTM30 Plus, a public domain dataset that combines sea floor and land elevation data of the entire world. CleanTOPO2 comes in three versions tailored to meet different design and production needs. All versions are 16-bit grayscale TIF files ...


4

http://www.naturalearthdata.com/downloads/ has 1:50M rasters of the Ocean Bottom (http://www.naturalearthdata.com/downloads/50m-raster-data/). All their data is public domain so there are no worries about licenses.


4

Worldwide bathymetry data in .nc extension format can be obtained from here at the following resolution: The GEBCO One Minute Grid — a global one arc-minute grid Released: 2003, updated: 2008 — largely based on the most recent set of bathymetric contours contained within the GEBCO Digital Atlas. The GEBCO_08 Grid — a global 30 arc-second grid You can ...


4

I believe you can use some map algebra (raster > raster calculator) before you can preform your volume measurements in grass. Assuming that your bathymetric data use positive values to represent the sea depth, and using your example for the range as 50 the min_depth and 200 the max_depth. For each of the raster cells you need to "remove" anything below the ...


4

What are your region settings? I tried this set of commands, and succeeded to create a DEM with negative values, with no problems: # Set region to low resoution GRASS 7.0.0 (ITM):~ > g.region -p res=5 # The contour vector GRASS 7.0.0 (ITM):~ > v.db.select test_ctours cat|elev 1|-100 2|-80 3|-60 4|-40 5|-20 # Create rasterized contours GRASS 7.0.0 (...


4

For Germany North Sea and Baltic Sea: Baltic sea IOW Baltic Sea Bathymetry Database Mark an area and download. North Sea AufMod sorry only german. DE: Alle morphologischen Produkte des Funktionalen Bodenmodells stehen über einen FTP-Server zur freien Nutzung zur Verfügung. Die Polygondaten stehen in der File-Geodatabase AufModDatabasedModelling.gdb über ...


3

Canadian Hydrographic Service may be your only choice, I'm afraid. LIO is supposed to have line and point bathymetry data, but their login and search tools are going off into hyperspace for me right now. My friend was lucky in that the lakes he was interested in had just had a very detailed survey in advance of the G8, and CHS (apparently) don't maintain ...


3

If you have access to the 3D Analyst extension, instead of downloading NetCDF grids, you could download ASCII grids (GEBCO offers both options). You can use the ASCII 3D to Feature Class tool to create a feature layer, and then use the Spline or Krigging tools to create your bathymetric rasters.


3

Try these links: IHO and NOAA Google bathymetric data download Bathymetry shape files here http://gcoos.tamu.edu/products/topography/Shapefiles.html


3

I found an open source (python, R, QGIS, and PostGIS) workflow by Michele Tobias, based on Dr Venkatesh Merwade's 2005 paper here: http://www.slideshare.net/MicheleTobias/open-source-workflow-for-surface-interpolation-with-curvilinear-anisotropy There is a Github project with documentation trying to turn this into a (very useful) Qgis plugin: https://github....


3

For ocean bottom basemap (no contours). I recently noticed the ocean basemap release. arcgisonline ocean (rest endpoint) There are some pointers for using it with other basemap extents and also, more information and several other good links for oceanic data (including disputed maritime boundaries) on the esri blog archives. Esri blog


3

The NOAA has an extensive collection of bathymetric data sources. I assume you are referring to bathymetric ocean data?


3

GRASS can do what you're asking. Here's how I would approach the mssion: First get or digitize the banks of the river as a (long, winding) polygon. Then import your xyz data as a point vector (v.in.ascii), and your river polygon in the appropriate GRASS location/mapset with v.in.ogr. Now you'll have to think about the region settings with g.region . You ...


3

You might like to check out one of the presentations at FOSS4GIS 2014 titled " Open Source Work-flow for Surface Interpolation with Curvilinear Anisotropy — Michele Tobias, University of California Davis." http://vimeo.com/106235881


3

GEBCO provides an homogeneous coverage of the world seabed.


3

There are many approaches you could use to extract portions of your surface model. With Raster Calculator, you could extract cells based on values. For instance, with the Con() statement you could do something like this: Con("CTM_Raster" <= -50, 1, 0) This will generate a new raster with a value of 1 for values less than -50, and 0 for those greater. ...


3

You are drawing a wedge through the hummocky splooge. The methodology is fairly crude, but without a "before".. you are just guessing so why waste a bunch of time. The points you proposed to create will be fine for the deep end of the wedge, but you will need a shoreline from old imagery (pre-slide) or getting something out of some vector data to use as ...


3

Another option you have is the ETOPO1 Global Relief Model. It has a 1-arc minute resolution (so slightly lower than the option above), but it comes in one complete file rather than 30 different tiles, so it may be easier to work with depending on what you are doing. It can also be downloaded as a georeferenced tiff that can easily be imported into ArcMap.


3

Another source is the General Bathymetric Chart of the Oceans. Their 30-arc second dataset is (in my limited experience) better than the SRTM data for bathymetry because they use data from actual ship depth soundings for bathymetry where available.


3

The datum will only be specified if the creator of the dataset put it in there. If you're given a dataset and it's missing the coordinate system, datum, or both (horizontal or vertical), you'll need to track down its origin (a parent dataset, the person who gave it to you, etc.) to find it. If that proves impossible, you may be able to make an educated ...


3

ArcGIS has a raster layer display resampling feature. Assuming the spatial resolution is the same for the input and output raster data, the 3D Analyst output likely has either Bilinear Interpolation or Cubic Convolution resampling applied to produce a smooth looking raster on-screen. You can apply the resampling (or check if the resampling is applied) in the ...


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