Tag Info

Hot answers tagged

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

First, you need to calculate at least the slope. F.ex I have the following data: Then put the correct data as variables to the module: And at last you should get the result: UPDATE With Catchment Area as input the results are:


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 ...


4

Based on your use-case, I'm guessing you won't need extremely high resolution data (many users are looking for 90 meter or better data) and are more interested in the consistency and visual presentation aspects of the data than its precise accuracy at a cell level. A nice dataset for this kind of use is CleanTOPO2, a global nominally 1km resolution dataset ...


4

You need to download the Land-Form Panorama OpenData (OpenData=free) dataset from Ordnance Survey Download is for Great Britain only (England, Scotland & Wales only) 530MB https://www.ordnancesurvey.co.uk/opendatadownload/products.html Pros: FREE This product is supplied both as a set of contours and spot heights (x,z,y) and as a gridded digital ...


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 ...


4

OK- I figured out a fix for this. Susan Jones has a script http://arcscripts.esri.com/details.asp?dbid=16055 that works the way I was hoping the Bearing Distance to Line tool would work. The output from the script were lines radiating at varying angles and distances from my base coordinate (datum). Then I used Feature Vertices to Point to add an X,Y ...


4

Hypsography concerns the land's elevation, altitude or height above sea-level or some other reference surface. (Hypso is derived from the Greek for height.) Topography concerns physical and cultural features of the land and so includes hypsography, hydrology, the built environment, major boundaries, communication channels, etc. (Topo is derived from the ...


4

You get this kind of picture because every file has a different range of gray values, and QGIS scales the colours between min and max seperately. To solve this: Create a virtual raster on all your files using GDAL, or from the QGIS menue. Load that instead of the individual files as one single layer.


4

Defining ridges vs hill/mountain tops is pretty scale-dependent. Jeff Jenness covers conceptually how to model topographic landforms in his article Some Thoughts on Analyzing Topographic Habitat Characteristics. If you poke around on his website, you can find his poster on this as well, under ArcGIS tools > Land Facet Corridor Designer. (Link is here) Jeff ...


4

SRTM (Shuttle Radar Topography Mission) was a shuttle mission, no satellite involved. But essentially the satellites do not cross the poles. In a geosynchronous orbit, which most imaging satellites are in, you get a pattern like: This great because it means that the orbit can be timed and most parts of the earch get covered at around noon, so good ...


4

Is Python an option? Use RasterIO (a Python GDAL/ numpy bridge) to load the raster to NumPy array, then use numpy.amax() to find the maximum value, followed by numpy.where() to find the row/column indices, then calculate the lat and lon from the raster extents.


3

The best all round tool here is a raster calculator. gdal_calc is a GDAL raster calculator implemented in Python here, with some examples here. If you e.g. wants to keep values above +50: gdal_calc.py -A input.tif --outfile=result.tif --calc="A*(A>50)" --NoDataValue=0 You can specify several files -A to -Z, where each of them get a corresponding ...


3

I would say that you're on the right track, and both slope and ruggedness would be useful for you. I'm not sure what angle cliff faces bats prefer but I'm assuming you know this. To perform a slope analyis, you will need either the Spatial Analyst Extension or the 3D Analyst Extension. You want to run the Slope Tool. Once you've performed the slope ...


3

It may not show up under the Basemap dialog, but Esri does host a US Topo map service. The service uses scale dependent rendering with 4 levels, a colorized shaded relief, 250k topographic, 100k topographic, and 24k topographic. ArcGIS.com http://www.arcgis.com/home/item.html?id=931d892ac7a843d7ba29d085e0433465 or ArcGIS Server REST endpoint ...


3

Another open source option which can easily be scripted using shell scripts or python is to use GDAL_Contour to generate contours from a dem file. I grabbed some example DEM data and ran this command to generate 10 m contours, saved as a shapefile: gdal_contour -b 1 -a elevation -snodata -9999 ns67ne.tif contour.shp -i 10 The switches are: -b 1 selects ...


3

I think that GRASS module r.contour has more functinality than QGIS' one. For example, you can set maximum and minimum levels for extracting contours. Plus, it has parameter cut which makes the output more generalized.


3

If I read correctly, you are looking for a replacement for the WMS service of the USGS Quad Maps. From what I can find, there doesn't seem to be a direct replacement for that. I think the closest you are likely to find is using the Seamlesss Data Warehouse. This is the USGS data portal for all the orthoimagery that they supply as well as their National ...


3

The add_edge method of a Graph in NetworkX takes a weight as an attribute. This is a proxy for traversal restriction. If the weight specified is high, then traversal algorithms will avoid that route. For example: import networkx as nx G=nx.Graph() G.add_edge('a','b',weight=0.6) G.add_edge('b','c',weight=0.2) G.add_edge('c','d',weight=999) # this one is ...


2

Those look like the grids for the National Topographic System in Canada. They can be downloaded from Geogratis as the Vector Indexes of the National Topographic System of Canada. There is a folder in there called kml_files full of .kmz files. If you prefer, you can get them more easily by downloading them zipped (15mb) at all scales from the WMS in ...


2

Are you looking for a height map or a topo map? These are not exactly the same. If you want a grayscale (or any other scale for that matter) height map of Britain, one of the ways you can get that is using Maperitive's generate-hypsometric command. Here's a sample heightmap I've just made for the northern Scotland (black is zero elevation, white is 1500m ...


2

I don't think there is a way of doing what you want, or if there is I don't know how to do it. Just at the moment I'm making eight maps that need this form of grid labelling and I'm having to add each grid ordinate as a label. It's taking me hours. It should be possible to exercise some control on where grid ordinate labels appear on the map, using a ...


2

It is. My opinion that these are flood control structures. Berms if-you-will? Here they are used as impervious (paved) runoff holding ponds along and near water tracks. Probably considered man made berm or control structure.


2

Please have a look at Using Viewshed and Observer Points for visibility analysis In the lower part of the article you will see that there are several parameters that you can use. The parameter that you need are VERT1 & VERT2 To use these parameters in your ViewShed Analysis, your input point featureclass should have fields with these names. The ...


2

1. Get the pixels value: gdal's gdallocationinfo allow to access a pixel's value. The gdallocationinfo utility provide a mechanism to query information about a pixel given it's location in one of a variety of coordinate systems. Several reporting options are provided. $ gdallocationinfo crop.tif 50 50 Report: Location: (50px,50line) Band 1: ...


2

If the shapefiles to be merged are in the same directory: ogr2ogr merge.shp levels001.shp ogr2ogr -update -append merge.shp levels200.shp -nln merge ogr2ogr -update -append merge.shp levels500.shp -nln merge ogr2ogr -update -append merge.shp levels1000.shp -nln merge ogr2ogr -update -append merge.shp levels2000.shp -nln merge


2

To start off, you have to choose a coordinate reference system. The one used by Openstreetmap (EPSG:3857 or 900913) does not have real meters as units, because the horizontal lengths (latidues) are all equally squeezed, while they are getting shorter towards the poles in reality. So you have to look for the UTM zone of your part of the world, or another CRS ...


2

Maybe offtopic, but please note this new release: "November 20, 2013 NASA SRTM V3.0 has eliminated all voids with fill primarily from ASTER GDEM2 (Global Digital Elevation Model Version 2), and secondarily from USGS GMTED2010 - or USGS National Elevation Dataset (NED) for the United States (except Alaska) and northernmost Mexico."


2

I recommend using Python or R (or a GIS software), as @Marc Pfister has suggested. However, you can do it with bash and gdal only, and heavy usage of grep. First get the Min/Max values without coordinates: Obtain the Min / Max values with gdalinfo or gdalinfo -mm like explained in your other question about Min/Max values. Use grep (and possibly some awk) ...


1

If ok to manage 872 tiles which can be later on unzip and gdal_merge, then : wget -r --no-parent --random-wait --timestamping -A.zip http://gis-lab.info/data/srtm-tif/ or curl -L 'http://gis-lab.info/data/srtm-tif/srtm_[01-72]_[01-24].zip' -o 'SRTM_V41_#1_#2.zip'



Only top voted, non community-wiki answers of a minimum length are eligible