Hot answers tagged dem
24
In my experience, DEM is most of the time used as a generic term for DSMs and DTMs. I think this image on Wikipedia depicts the differences between DSMs and DTMs well:
DSM = (earth) surface including objects on it
DTM = (earth) surface without any objects
A different definition is found in [Li et al., DIGITAL TERRAIN MODELING - Principles and ...
21
Begin by considering the type of dam construction. Some dams are high, thin, and curved; others--including earth dams, which are perhaps commonest--tend to be straight across and quite thick, with slopes that vary from 1:2.5 to 1:5 (40% to 20%). For many examples, see the illustrations in B. Bassell's 1904 study on earthen dams.
You need to create a DEM ...
16
How about John Stevenson's r.denoise, from the GRASS AddOns wiki:
r.denoise denoises (smooths/despeckles) topographic data, particular
DEMs derived from radar data (including SRTM), using Xianfang Sun's
denoising algorithm. It is designed to preserve sharp edges and to
denoise with minimal changes to the original data.
I read further from this ...
15
Digital elevation models (DEM) are a superset of both digital terrain models (DTM) and digital surface models (DSM). Remote sensing generally captures the surface height, so the top of the tree canopy or buildings is returned, not the bare ground elevation. If this data is corrected to remove elements which extrude above the terrain height, you're left with ...
13
In my experience, a more complete answer to this question lies in defining the difference between a DEM, DTM and a DSM. A DTM is NOT a generic name covering both DEMs and DSMs. So...
A DEM is a 'bare earth' elevation model, unmodified from its original data source (such as lidar, ifsar, or an autocorrelated photogrammetric surface) which is supposedly free ...
12
Convert your stream vectors to raster with a value of 1 and the same extent and cellsize as your DEM. In the Raster Calculator use a map algebra expression something along the lines of:
Con("rivers"==1, "DEM" - 1, "DEM")
If you want to burn in the streams more than 1 elevation unit, change "DEM" - 1 to "DEM" - a bigger value.
To implement the Whitebox ...
10
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 ...
9
Cartographic rules to represent the relief as contours are presented in Imhof's famous book on relief representation, chapter C. Some of these rules are given on this wikipedia page. The main recommendation when simplifying contours it to preserve the terrain main characteristics.
Smoothing the contours independently do not prevent them to overlap: It is ...
9
You can go to Data Management -> Raster -> Raster Processing -> Clip, and Spatial Analyst is not needed.
There just check the checkbox "Use input features for clipping geometry".
From help: If the checkbox "Use input features for clipping geometry" is checked, then the output raster is clipped based on the perimeter of the polygon shape. If the checkbox is ...
8
GRASS has r.fill.dir and better yet, r.terraflow, which is one of the few hydrology tools to work on massive rasters. There's also the Windows-only TauDem, which includes PitRemove for filling.
8
GDAL is your friend. As Brian said, if you reproject one tile at a time, they won't mosaic very well due to rounding errors. But instead of mosaicking them into a big GeoTIFF first, a quicker and more disk-friendly way would be to use the gdalbuildvrt program to generate a "virtual raster" that is just an XML file listing the source images, but has the ...
8
This is a job for the Raster Calculator, it's under the Raster menu (don't confuse this with RasterCalc!). The expression:
snowdon_dem.tif@1 + 10
will do this, where 'snowdon_dem.tif@1' is the name of the original DEM.
You can also find additional informations here.
Nick.
7
For relief shading in GRASS, better use r.shaded.relief. It comes by default with light from west to east. Like this (SRTM example):
For my perception the valley looks ok in this example. The colortable comes from r.colors (there are "terrain" and "srtm", see here for examples of these color tables).
7
The GRASS command r.profile performs this (documentation, source) and should provide a good basis for implementing a cross section, and is available under the GPL.
7
SAGA GIS has a module for this: Interactive profile
http://www.saga-gis.org/saga_modules_doc/ta_profiles/index.html
The resulting points will contain the distance and the overland distance. If the DEM has a coarser resolution your overland distance will always be a bit lower (unless you have strange border conditions), but in reality this difference is ...
7
If you don't have this capability built into your GIS, but you can perform some basic grid operations ("map algebra"), there is still a solution.
The calculation comes down to finding the slope of the route at every point. If you knew this exactly, with no discretization error, you would integrate the secant of the slope. On a grid, the integral is ...
7
You need to use a conditional operator. The logic is:
Result = If {new DEM has values, use them}
Else {use values from the original DEM}.
Alternatively, this can be expressed as
Result = If {new DEM does not have values, use original DEM}
Else {use the new DEM}.
In ArcView the syntax varies with the version: there's one syntax for ...
7
gdal_translate will work using the -srcwin or -projwin options.
-srcwin xoff yoff xsize ysize:
Selects a subwindow from the source image for copying based on pixel/line location.
-projwin ulx uly lrx lry: Selects a subwindow from the source image
for copying (like -srcwin) but with the corners given in georeferenced
coordinates.
You would ...
7
I'm guessing the horizontal units for your raster are in either degrees or arcseconds. You need to reproject this raster to a spatial projection where your horizontal and vertical units are the same (i.e., if the vertical units are in metres, then I suggest using UTM, which has horizontal units of metres).
To reproject a raster with ArcCatalog/ArcGIS, look ...
7
Whitebox GAT (open-source hydrology and remote sensing package) has a method by this name in its Hydrology utilities. Whitebox is unique in that it exposes the source code and algorithms used by the analysis via the UI (note the View Code button). Even if you intend to isolate your procedures to ArcGIS, there may be some benefits to experimenting with ...
7
Your surmises are correct. Checking for symmetry is an excellent idea: (Gaussian) curvature is an intrinsic property of a surface. Thus, rotating a grid should not change it. However, rotations introduce discretization error--except rotations by multiples of 90 degrees. Therefore, any such rotation should preserve the curvature.
We can understand what's ...
7
You could start by getting the difference of the two DEMs. QGIS has a raster calculator tool that should come in handy. Just get tiles of both DEMs that cover the same area and subtract the values of one DEM from the other. That should get you a nice raster layer that shows the differences in elevation between the two DEMs.
7
As Vladimir has suggested, you can do that by making sure they are using the same color table. You can do this by loading both DEMS in QGIS, then right clicking the DEM that has the color table you like and copying its style. You then select the other DEM, right click it and paste the style.
6
SAGA has several fill methods
http://www.saga-gis.org/saga_modules_doc/ta_preprocessor/index.html
Flat Detection
Sink Drainage Route Detection
Sink Removal
Fill Sinks (Planchon/Darboux, 2001)
Fill Sinks (Wang & Liu)
Fill Sinks XXL (Wang & Liu)
6
@jul is correct that "you need to compute a trend surface, and then subtract it from your initial DEM to obtain the 'detrended' one," but it sounds like simpler procedures are needed in this case to "preserve the dips." If the "trend surface" too closely follows the original DEM, then the residuals will not retain the local characteristics of the surface. ...
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
I believe you are just looking for the 60th percentile value for your raster. The easiest way to do this probably is through the histogram functionality. Right click on the layer in the Table of Contents, then go Layer Properties > Symbology > Classified > Classify. Choose Quantile as the Method, and use 10 classes. The 6th class will then begin at the ...
6
you are searching Extensions > 3D Analyst > Interactive 3D analysis tools.
How to create a profile graph from digitized features of a surface
1.In ArcMap, click the Layer drop-down arrow on the 3D Analyst toolbar and click the
surface that you want to profile.
2.Click the Interpolate Line button Interpolate Line button.
3.Click the surface and digitize ...
6
In the GRASS GIS Wiki, there is a dedicated page for this: http://grass.osgeo.org/wiki/Contour_lines_to_DEM The page demonstrates and compares a number of different methods of converting vector contour lines into raster DEM surfaces including screenshots.
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