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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1answer
448 views

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 ...
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1answer
4k views

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 = ...
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1answer
439 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 ?
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4answers
3k views

Add UTM labels to grid in qgis

I try 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 ...
3
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0answers
133 views

How to compute surface of raster or any point using ARCGIS?

I have a raster image whose values are a digital elevation model of terrain. I need to know the surface type (topographic characterization) of particular points along transects of this DEM. How to ...
3
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1answer
602 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 ...
11
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5answers
7k views

How to calculate Topographic Ruggedness Index in ArcGIS Desktop?

Does anyone know how to calculate Topographic Ruggedness Index in ArcGIS without access to command line ArcInfo Workstation? "The topographic ruggedness index (TRI) is a measurement developed by ...
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2answers
244 views

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 ...
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0answers
499 views

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 ...
5
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2answers
1k 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 ...
3
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1answer
1k 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: ...
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2answers
395 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: ...
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1answer
224 views

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 ...
2
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1answer
296 views

Negative Topographic Index Values

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 ...
2
votes
2answers
168 views

Gdal: highest and lowest point/pixel, how to get their altitudes?

Given a .tiff topographic raster image. How to get the altitudes of the highest and lowest point/pixel ?
2
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2answers
630 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 ...
2
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2answers
409 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 ...