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18

There are different possible implementations, but most procedures will start from a grid and not from a TIN. The simplest one is most likely the D8 procedure: you calculate the direction where water would be flowing. There are 8 possibilities, the 8 cells that are next to a central grid cell. You can first calculate these directions, than how cells are ...


13

Curvature is a complex terrain derivative to compute, the equation that you use depends on the resolution of your input data, as you have to ensure that the curvature results you compute can be distinguished from noise in the data. A lot of research has been done recently on curvature calculations on high resolution LiDAR data which showed that a scaling ...


12

It is all very dependent on your needs. You know that TIN is a vector-based representation whereas DEM is represented as a raster from grid of squares. Actually TIN is a type of DEM and derived from the raster DEM. The TIN representation has information about altitude, slope and aspect and you can use them to extract the areas you require. There is an ...


10

ESRI's version of Raster Analysis for calculating curvature might be helpful to develop a plugin for QGIS. For each cell, a fourth-order polynomial of the form: Z = Ax²y² + Bx²y + Cxy² + Dx² + Ey² + Fxy + Gx + Hy + I is fit to a surface composed of a 3x3 window. The coefficients a, b, c, and so on, are calculated from this surface. The ...


9

There are several open data initiatives on elevation (terrain) data. A website with several alternatives (I have not checked them all) is available on this website: http://www.terrainmap.com/rm39.html For 90 meter accuracy dataset I would try the Shuttle Radar Topography mission (wikipedia article). I have used it on several occasions. An example of ...


7

The algorithm is fairly simple. In a nutshell, it searches different possible platform elevations, computes the cut volume, dumps that into the fill area, and checks whether there is any left over or lacking. In detail, the algorithm deals with a digital representation (TIN or grid) of an idealized surface which we can think of as the graph of an ...


7

Here's a great resource on terrain generation algorithms and software on vterrain.org: http://vterrain.org/Elevation/Artificial/


6

ArcGlobe http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=ArcGlobe_3D_display_environment Lots of RAM required. Though Google Earth might be a better option. (as comes with a flight sim) http://earth.google.com/intl/en/userguide/v5/flightsim/index.html


6

TopOSM has terrain tiles - though limited coverage (US Only) http://www.toposm.com/us/ Full Details http://wiki.openstreetmap.org/wiki/TopOSM All the Rendering and Source files are available http://svn.openstreetmap.org/applications/rendering/toposm/ License is the same as Open Street Map OpenStreetMap Data is available under the Creative Commons ...


6

Mike Migurski (of Stamen Design) recently made a major new open terrain map: details on his blog and I put up a quick map viewer for it. It does terrain relief shading with various DEM sources combined with roads, labels, etc from OpenStreetMap. The source code to generate the map is on GitHub.


6

Compute the focal range grid using a 2 x 2 neighborhood. (Use the option where NoData cells are ignored.) Any two adjacent pixels will be included within at least one neighborhood. Therefore, if any pair of cells differ by more than 16 m, they will cause at least one surrounding neighborhood to have a focal range exceeding 16 m. If the focal range of a ...


6

I think gdal_tranlate is going to be your best bet. I too am having to do this now to get elevation data in Vue for 3D simulations. Right now, I am going from whatever grid format to tif, then using gdal_translate to go to dem. If there is a way to do this natively using ESRI tools, I'd love to know about it. You can use the -projwin flag to clip as you ...


6

You could also consider having a script that takes random part of an existing real DEM.


5

You can generate your own using Maperitive: generate-relief-igor command generate-tiles command A sample hiking map using such tiles.


5

I provide a number of sample LiDAR files at http://liblas.org/samples that you can download. These are mostly example data, but many are quite interesting. You can use the las2txt utility that libLAS provides (or Isenburg's las2txt version as well) to convert them to XYZ ascii files. Isenburg's tools also provide a number of fantastic triangulation ...


5

ArcGIS claims to be able to do this at 10 with new 3D Analyst tools: Virtual City Template Enables 3D City Modeling. I say claims because I haven't personally used these tools yet. Here's the documentation for the tool discussed in that article: How Skyline Barrier (3D Analyst) works


5

An original approach is the one proposed in this paper: Fisher, P., J. Wood, and T. Cheng (2004). Where is Helvellyn? Fuzziness of multiscale landscape morphometry. Transactions of the Institute of British Geographers 29, 106-128. It proposes a method based on fuzzy and multi scale representation. I am not sure but this method may be the one implemented ...


5

I actually like using the Rugosity index from Lundblad et al. http://dusk.geo.orst.edu/esri04/p1208_cc.html http://proceedings.esri.com/library/userconf/proc04/docs/pap1208.pdf (I think this was only published as a paper presentation, but it is one of the most cited posters in oceanography.)


5

try or read this page for some good information. and second link show you the way of random digital elevatin model... Numerical and Scientific Python and Data Visualisation creating elevation/height field gdal numpy python i hope it helps you


5

You can use fractals for this: . The upper row was generated with the fractal dimension d=2.0005 (left: elevation map, right: aspect map), the lower row with fractal dimension d=2.90 (left: elevation map, right: aspect map). I used r.surf.fractal of GRASS GIS. Then simply export the artificial DEM with r.out.gdal (or the GUI) to GeoTIFF.


5

I've done maps like this before in ArcGIS years ago. I would clip the elevation raster (usually NED from USGS) to the vector polygon of the study area. Next, create a hillshade of the elevation raster, drape that over the source NED raster, then play around with the transparency/contrast/color ramp of the hillshade to get it to look like I wanted - you might ...


5

Natural Earth has many top-notch free products that may work for you, including: Natural Earth I with Shaded Relief, Water, and Drainages Shaded Relief Basic


5

ArcInfo Macro Language (AML) is old in ESRI Terms though it is possible to run .amls in ArcGIS 10.0 if you have the right requirements: It's possible to use ARC Macro Language (AML) files in the ArcGIS Desktop environment by creating a new geoprocessing script tool. If you have an ArcInfo license and ArcInfo Workstation installed, you can add a custom ...


4

It seems like there should be a way to derive AS from a skyline graph created using the ArcGIS 10.0 3D analyst. If you have a skyline (3D polyline) that surrounds an observation point, it should be able to step through each vertex on the skyline and find some portion of a sphere that is visible. Or, if you moved each vertex so that it is one unit ...


4

If you have access to arcinfo-workstation (that is: command line arcinfo) then use the LATTICEDEM command to convert from raster to USGS DEM. If you have Arcinfo License level then workstation is available from the original installation media (up to v10.0) but isn't installed by default. Arc: latticedem Usage: LATTICEDEM <in_lattice> <out_dem> ...


4

The paper "Multiscale Analysis of Topographic Surface Roughness in the Midland Valley, Scotland" by Grohmann et al., 2011 describes the differences between a six methods of calculating surface roughness measurements from 2D digital topography. His paper was helpful since he provides a quantitative comparison of each method using a single test region at ...


4

Have you tried to perform any histogram stretching? If you are using a raw satellite image it will be less visually appealing without any stretching. If you are thinking of using osgearth I would assume that you are using the satellite image for a 3D application? I have worked in the 3D visualization industry for the better part of a decade and all raw ...


4

You've got a projection issue. Chances are you've not specified the projection of the DEM correctly. There are typically two indicators to this and you have both: You have spikes. You have a cell size that looks like: 0.000278 (it should be a whole number). So make sure you've set the correct projection for the DEM as well as the drape (if memory serves, ...


4

In this Wiki we maintain a list of free data sets: http://grass.osgeo.org/wiki/Global_datasets#Elevation_data For several also the import commands for GRASS GIS are stated (in many cases read with GDAL, hence the GDAL tools should work as well).


4

You should not be seeing negative values in the CTI. Since you did not provide a reproducible example I cannot speculate as to why you are getting incorrect results. The expected range is not limited 1-10. The range will be defined by flow accumulation which is influenced by the size of the basins that are accumulating flow. The index does not rely on washed ...



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