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15

Imagine several satellites spread out evenly above you. Now pick just one satellite. Visualise a sphere centered around that satellite with a radius of your exact distance from it. Do the same for every satellite in view. What you're seeing now is a bunch of spheres that intersect exactly where you're standing. That's how a GPS reading works, ...


13

The 3-arc second (~90 meter) SRTM covers all of Europe to 60° N, has good positional accuracy and is part of the public domain. CGIAR provides an interface for easily downloading the data tiles, which are provided in both ASCII and GeoTIFF formats.


13

My suggestions would be to utilize reverb at http://reverb.echo.nasa.gov/reverb/. First register if you have not already done so. In the search box type ASTER GDEM and Select Dataset --- note if you want a particular area this is the point where you select the box range in the map window to the left (very useful feature!). ASTER GDEM Global Digital ...


11

I would recommend to look outside ArcGIS) Very easy using the free gdal software: http://www.gdal.org/gdaldem.html gdaldem TRI input_dem output_TRI_map Or if you'd prefer it in saga gis: http://www.saga-gis.org/saga_modules_doc/ta_morphometry/ta_morphometry_16.html


10

Let's do a little (just a little) algebra. Let x be the value in the central square; let x_i, i = 1, .., 8 index the values in the neighboring squares; and let r be the topographic ruggedness index. This recipe says r^2 equals the sum of (x_i - x)^2. Two things we can compute easily are (i) the sum of the values in the neighborhood, equal to s = Sum{ x_i ...


10

If you are looking to convert DEMs to contour lines: QGIS Plugin Contours For converting scanned topo maps to vector contour lines, Arcscan is one of the easiest (and most sophisticated) programs out there. However, there are several opensource alternatives, including a promising GRASS approach: Trace vector contours from a scanned map. Additional ...


10

The highest elevation within 10 km is the neighborhood maximum value computed with a circular 10 km radius, so just extract a profile of this neighborhood maximum grid along the trajectory. Example Here is a hillshaded DEM with a trajectory (black line running from bottom to top): This image is approximately 17 by 10 kilometers. I chose a radius of ...


9

Maybe QGIS "Profile" plugin source code can be a start.


9

For a local solution, GRASS can be scripted to do this: # extract raster values at our points # use cubic convolution for interpolation between DEM locations v.drape in=my_pts out=pts_srtm_elev type=point rast=srtm_dem method=cubic I ran an extended version of this for one of my use cases and performance of v.drape was no issue at all.


9

Following on from the comments, here's a version that works with perpendicular line segments. Please use with caution as I haven't tested it thoroughly! This method is much more clunky than @whuber's answer - partly because I'm not a very good programmer, and partly because the vector processing is a bit of a faff. I hope it'll at least get you started if ...


8

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.


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

Elevation can be extracted (x,y,z values) from ETOPO1 is a 1 arc-minute global relief model of Earth's surface that integrates land topography and ocean bathymetry. It was built from numerous global and regional data sets, and is available in "Ice Surface" (top of Antarctic and Greenland ice sheets) and "Bedrock" (base of the ice sheets) versions. Historic ...


7

Download the source code from here http://www.osola.org.uk/elevations/index.htm SRTMGeoTIFFReader.php is the clever file the reads the GeoTiff and converts the elevation values (in meters) into Lat/Lng coordinates. I doubt this is exactly what you want but it does give you a solid base on understanding the process required to accomplish the task from your ...


7

I usually come at this question from the angle of "what is going to enhance, and not obscure, my data?". Tufte talks about the some of the uses of colours in maps: to label, to measure, to represent, and to enliven. Choosing DEM colours is usually mostly for the latter (enlivening) - to make them look nice. For example, the default 'atlas coloring' of many ...


7

I would highly recommend going through the Contour lines to DEM tutorial, available from GRASS wiki. Essentially, they describe different interpolation methods used to produce a DEM. Avoid IDW interpolation using contour lines (i.e. described in one segment of the tutorial) since this is an inappropriate use of the interpolation method. The GRASS module ...


7

As a geologist, I often use this technique to make geological cross section in pure Python. I presented a complete solution in Python: Using vector and raster layers in a geological perspective, without GIS software (in French) I present here a summary in English: to show you how to extract the elevation values ​​of a DEM how to treat these values If ...


7

I think I can answer it for you. If you look at the precision vs. accuracy image on the link you provided, precision refers to the repeatability of the observation. For example, if I measure the distance from one point to another and it is always vaying only by a very small amount, then I am making measurements at a high precision. But, basically, ...


7

One thing to keep in mind is that lat/long is geodetic and not geocentric: If we were to calculate elevation as a radius from the center of the ellipse, our elevation lat/long would be different than our horizontal lat/long! This is why there are two different datums. The horizontal datum is just a smooth ellipse, because it's easier to do trig ...


6

I would say this depends on your knowledge of the data and how it was collected as well as how the DTM was generated from the raw data (regular grid vs interpolated from irregular points or other sources) I don't think there is a rule of thumb. Personally, I choose contour intervals based on the scale, type, content, purpose of the map, etc.


6

Searching Google with "Trinity High-Water Mark" in quotes (and adding London or Thames) returns a bunch of Google Books results from the 19th century. My favorite is this transcript of the Reports from Committees for the Great Britain House of Commons:  5838 . Mr. Forsyth.] Is the Trinity a datum level ? -- The Trinity high-water mark is the datum. ...


6

An elevation profile computes the intersection of two surfaces. One of them is a vertical sheet determined by a path. (That is, it consists of all coordinates (x,y,z) where (x,y) is on the path and z is any number.) The other is the surface represented by the raster DEM. As such, it amounts to finding the z-values lying above points on the curve. This ...


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

Here's a start (not really tested...) First two assumptions: I guess your tracks table is a PostGIS spatial table, with a geom column? (If not you'll have to run SELECT AddGeometryColumn(...) to set it up using the Lon/Lat values) When you say "incremental distance" I'm assuming you mean accumulated distance? I made two test tables: tracks for the ...


6

If you really want a text-based raster.. whuber is quite right about a text-representation of raster data being inefficient. But at the same time, it can help to "see the data" when it's represented in text, especially while you're cutting your teeth on some concepts So in the spirit of endorsing text-based-raster for some purposes, you might want to check ...


6

Data format I'll take it as a little exercise in how to program a data reader. Have a look at the documentation: SRTM data are distributed in two levels: SRTM1 (for the U.S. and its territories and possessions) with data sampled at one arc-second intervals in latitude and longitude, and SRTM3 (for the world) sampled at three arc-seconds. Data are ...


6

To expand a little on Ryan's answer, a raster DEM is just like many other rasters, it contains a numeric value for each cell. That value could be elevation in feet, temperature in degrees C, or anything else that can be represented numerically. Reprojecting it to another coordinate system would not change the values in the raster cells, because GIS doesn't ...


6

Creating watersheds should help you locate both ridges and hill top. Then, I would define a hill top as a local maximum, while a point on a ridge is not the maximum (there is one other point higher or equal to this point). You can identify local maxima using the focal statistic tool. another way to look at the problem is to analyse at the opposite of your ...


5

Another api that you can query instead of google's is the US Geological Survey Elevation Query. Information about their service can be found here: gisdata.usgs.gov/XMLWebServices/TNM_Elevation_Service.php A request looks like this: ...


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



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