Hot answers tagged elevation
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.
10
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 ...
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 ...
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.
8
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
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.
8
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 ...
7
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 ...
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
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
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 ...
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
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 ...
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
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 ...
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
5
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 ...
5
i think this is a normal elevation error. if you check any validation report of GDEM2, you always see that it is reported Standart Deviation (SD) is to 12.7 m. whereas version 1 is 15.4 meter.
The ASTER GDEM version 1 was released in July 2009 and the version 2,
now under processing, will be released in the October 2011. The GDEM
version 2 is ...
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
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 ...
5
Sub-centimeter elevation? No.
This article provides a good overview of LiDAR and the associated errors (Range, Position & Orientation).
Operationally, when working with LiDAR data we assume a potential 5-10cm vertical and horizontal error. At times it may be much more accurate, but it's not sub-cm.
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
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 ...
4
If you want create a profile of maximum quality, then your algorithm has to basically include every single cell that is intersected by your query path and then it becomes a simple 2D curve fitting problem. However, if you want to just sample a subset of those points and create a profile that is more visually pleasing, you may that find that this paper from ...
4
SRTM data is easy to download for a given area, I've use this site in the past. The files aren't huge, and you can get them as georeferenced TIFFs. Downloading the whole world might take a while, but a couple of tiles covers a pretty large area. The issue you might have is with horizontal resolution, which is about 90 metres for most of the world, and the ...
4
Also according to my experience Aster-generated dems are noisy. I usually try to run a low pass filter to smooth the data from the command line window. Anyway, I don't think you will be ever able to obtain good 1m contour lines from Aster (noise, pixel size of 30m, low precision ecc ecc)! I guess you need another source...
4
Here's a more programmatic way of using GDAL than @Aragon's answer. I've not tested it, but it is mostly boiler-plate code that has worked for me in the past. It relies on Numpy and GDAL bindings, but that's about it.
import osgeo.gdal as gdal
import osgeo.osr as osr
import numpy as np
from numpy import ma
def maFromGDAL(filename):
dataset = ...
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