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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257 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
245 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
2k 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 ...
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0answers
117 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
326 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 ...
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2answers
102 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
293 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 ...
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2answers
304 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 ...
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1answer
906 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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1answer
2k 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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2answers
246 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
135 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 ...
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2answers
96 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
338 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 ...