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Questions tagged [topography]

The study and mapping of land surfaces, including relief (relative positions and elevations) and the position of natural and constructed features.

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How to conditionnally assign a new value to pixels of a raster image?

Given a topographic GIS raster of one country crop.tif: Given a know pixel value such as elevation (z) is +73 : $ gdallocationinfo crop.tif 1 1 -valonly > 73 Given an elevation threshold n = 50 (...
Hugolpz's user avatar
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7 votes
2 answers
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What is Google source for United States topographic data? [closed]

I'm looking for as detailed as possible topographic data for a certain area and have found information displayed by Google Maps to be far more detailed than what is provided by 7.5 minute maps (from ...
James's user avatar
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6 votes
5 answers
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Adding UTM labels to grid in QGIS

I am trying to use QGIS to create a custom topographic map for outdoor use: UTM, 1:50000. What these maps usually have is a 1km x 1km grid, which at the bottom is labeled with a shorthand for the ...
Lagerbaer's user avatar
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4 votes
1 answer
15k views

Assigning z values to depth curves in QGIS

I'm new to QGIS and working with GIS in general (as a student of architecture). I have obtained shapefiles with topographic curves of an ocean floor. My intention is to export these as CAD files and ...
erik's user avatar
  • 151
18 votes
5 answers
26k views

Calculating Topographic Ruggedness Index in ArcGIS Desktop?

Does anyone know how to calculate Topographic Ruggedness Index (a.k.a Terrain R.I.) in ArcGIS Desktop without access to command line ArcInfo Workstation? "The topographic ruggedness index (TRI) ...
matt wilkie's user avatar
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6 votes
1 answer
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Gdal_polygonize: How to filter pixels above a given value (elevation)?

Given a topographic GIS raster of one country: Given an elevation threshold n = 50 (meters) How to polygonize pixels when z >= n ? gdal_polygonize.py is not clear on this point. It states This ...
Hugolpz's user avatar
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3 votes
1 answer
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Can Compound Topographic Index (CTI) / Topographic Wetness Index (TWI) produce negative values?

I am calculating Topographic Wetness Index for a study area using SRTM DEM (90 and 30m). I've seen several versions of TWI (CTI). I have been using: TWI = ln(As +1 / tanB) where As = ...
derelict's user avatar
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3 votes
1 answer
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Seamlessly merging USGS DEM data with higher resolution survey?

I have a 10m USGS DEM for my entire map extent (~100sq miles) Inside of that, I have specific regions of higher quality GPS point data. (From a rover using a OPUS corrected RTK base station) How do ...
user83852's user avatar
2 votes
1 answer
2k views

Gdal: How to get a pixel's value from raster image?

Given a topographic raster image. Given a pixel's coordinate in pixel/lines or geocoordinate. How to get it's pixel value ?
Hugolpz's user avatar
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13 votes
5 answers
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Gdal: how to get the max and min altitudes of my topographic raster?

Given a .tiff topographic raster image. How to get the altitudes of the highest and lowest point/pixel ?
Hugolpz's user avatar
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Is there a difference between the Planchon & Darboux and Wang and Liu depression filling algorithms? Other than speed?

Can anyone tell me, based on actual analytical experience, if there is a difference between these two depression filling algorithms, other than the speed at which they process and fill depressions (...
traggatmot's user avatar
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10 votes
1 answer
6k views

Getting Negative Topographic Wetness Index (TWI) values in SAGA GIS?

I am getting negative topographic index wetness values in SAGA GIS - anyone else every get this? Not all negative values, but the minimum of the TWI range is negative for some steep watersheds we are ...
traggatmot's user avatar
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5 votes
1 answer
1k views

Topographic Position Index unexpected result in QGIS

I am using Windows 7 enterprise and QGIS version 2.12.2 Lyon. Have found an unexpected result when I use QGIS to generate a topographic position index (TPI) raster from a 30m by 30m DEM. I find a ...
trilobite's user avatar
2 votes
2 answers
778 views

QGIS color polygon according to points

I have two layers. Layer 1 contains points (x,y) and layer 2 contains one polygon. All points in layer 1 are positioned within the polygon of layer 2. The points in layer 1 contain an attribute with ...
Stücke's user avatar
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1 vote
1 answer
151 views

Summarizing flatness of county with statistic Elevation variance per square mile

I need to classify every county in the US as either hilly, moderately hilly, or flat. Accuracy is not critical, just a rough classification. I used R and followed the advice in this answer to import ...
Ben Hendel's user avatar
11 votes
2 answers
3k views

Fistance when viewing scaled-topographic map

A close friend from my company asked me a question about a topographic scaled map (1:25.000): What was the altitude to a location in km (as you are viewing Earth from space) when he was viewing the ...
urcm's user avatar
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9 votes
4 answers
6k views

What's the difference between hypsography and topography?

I've recently come across some data that has been labeled "hypsography". I looked it up and it sounds like topography. But this data source has data labeled "topography" separate from its "hypsography"...
boulder_ruby's user avatar
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8 votes
2 answers
10k views

How to create a crisp topographical/terrain map with ggplot2?

I am trying to produce a high quality vector based map (in greyshades) in order to report locations. I tried this by getting maps from GADM and SRTM to make a raster as a base for plotting in ...
Tony's user avatar
  • 81
8 votes
2 answers
9k views

How do you identify ridges on an elevation raster?

I was wondering whether anyone might be able to tell me in layman's terms how to extract or differentiate between ridges and hilltops from 10m elevation data using ArcGIS 10.1?
user27103's user avatar
7 votes
1 answer
27k views

Plotting elevation maps and shaded relief images from latitude, longitude, and elevation pairs [closed]

I have a set of latitude, longitude, and elevation pairs (roughly a grid of such values, though it is not uniform), and I'd like to be able to plot an elevation map and perhaps also a shaded relief ...
gammapoint's user avatar
6 votes
1 answer
2k views

How to create a buffer on a linestring with varying or increasing/decreasing width

I want to buffer rivers/streams for a topographic map. I'm using a PostgreSQL/PostGIS database. Usually, I create buffer with ST_Buffer with a constant width. For example, the width of a river buffer ...
Stefan's user avatar
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5 votes
2 answers
6k views

Can we create topographical map of private land using GPS elevation data?

Is there a way to create a relatively precise topographical map of a private land using GPS elevation data? As the land is a little bit over 100,000 square meters, the available regional topographical ...
lpfavreau's user avatar
  • 171
4 votes
1 answer
2k views

Mapping points from total station data in Angle, Horizontal Distance, Vertical Distance

I am working on creating a contour map from total station topo points in ArcGIS 10. The points were collected using H angle, HD, VD instead of XYZ points. I need to create points from these ...
awestriker's user avatar
4 votes
4 answers
2k views

Identifying highs on DEM using ArcGIS Spatial Analyst?

I have a DEM and I want to find each hill and create a polygon for its area, effectively the out closed contour that encloses the hill. I can do this visually but I'm about to work on a larger area so ...
whatahitson's user avatar
  • 1,896
3 votes
2 answers
1k views

GDAL Conversion of US Topo GeoPDFs

I've used GDAL_translate with "--config GDAL_PDF_LAYERS" option to convert US Topo GeoPDFs to GeoTIFF and it works great for creating collarless topos based on the new format. However, I can't get it ...
JRigs's user avatar
  • 31
3 votes
1 answer
3k views

Map Grid Index / Reference for Canadian Topo Map

Does anyone know where I can find some KML at different resolutions to show the grid reference for the Canadian topographic maps (CanTopo and toporama). Much like is displayed on the map here: http://...
Gavin's user avatar
  • 525
3 votes
1 answer
639 views

How big is the error of relative elevation between two points taken from GPS relative to taken from a topographic survey?

I am sufficiently familiar with the fact that a GPS is not supposed to be used to measure elevation of a point, since it gives the elevations relative to a reference ellipsoid, not relative to MSL of ...
rodrikev's user avatar
  • 500
3 votes
2 answers
2k views

Gdal: How iterate through all pixels of a raster image?

Given a topographic raster image. How to iterate through all pixels of this raster image ? Solution preferably with gdal, in console. Some other libraries/script could be installed. Related: Gdal: ...
Hugolpz's user avatar
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3 votes
1 answer
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Topography: How to convert raster into vector layers?

(nb:This project is part of the #Wikipedia #wikimaps project) 1. Question: How to create vector topographic maps from raster image ? How to convert raster topographic image into closed vector ...
Hugolpz's user avatar
  • 2,653
2 votes
2 answers
751 views

A library/software to create DEM from a topographic map

In one of my projects I need to digitize video clips showing some natural landscape. Specifically I need to know distances between different areas and elevation levels. I have a topographic map of ...
Flot2011's user avatar
  • 257
2 votes
0 answers
1k views

Why does the "local maxima" module in SAGA GIS put so many "maxima" points on lakes and plains?

SAGA GIS puts too many maxima points on plains and lakes. Why does it happen? Is there a way to avoid this? It's not really a big problem (the value is correct) except for the size of the SHP files in ...
Piotr Sadowski's user avatar
2 votes
1 answer
2k views

GeoTIFF height map banding/terracing

I'm getting pretty bad banding, terracing, low resolution appearance when importing height maps to QGIS. I've searched the forums and haven't found a solution to this. Attached are the original USGS (...
Pledwards's user avatar
1 vote
1 answer
406 views

How to fix unusual initial DEM input values and derivative raster output values in SAGA GIS without rescaling?

I am trying to run elevation derivative tools on a provincial DEM provided by the Ontario Government website (Ministry of Natural Resources and Forestry) and I am getting strange values when bringing ...
ATomz's user avatar
  • 91
1 vote
3 answers
2k views

Where can I programmatically download SRTM_V4.1 data?

SRTM v4 is an effort by the folks at CIAT-CSI to scrub, polish, and remove gaps in the raw SRTM data released by NASA (SRTM 3). One userfriendly interface : http://dwtkns.com/srtm/ provides ...
Hugolpz's user avatar
  • 2,653
1 vote
0 answers
301 views

Why does no line appear when using Interpolate Line in ArcMap? [closed]

I'm attempting to make an elevation profile from a DEM in ArcMap using the Interpolate Line tool. I've done this before, and it has worked great--basically I just draw a line with Interpolate Line, ...
user150886's user avatar