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Questions tagged [aspect]

The compass direction that a topographic slope faces, usually measured in degrees from north.

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Extracting slope of aspect information using QGIS?

In What is SOA (slope of aspect)? @Spacedman explained to me what SOA means. Now I need help to understand how I could work with it and extract the data that I want. I want to use Qgis (with Grass ...
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1answer
43 views

What is SOA (slope of aspect)?

I’m reading an article that the authors talk about extracting values of SOA (slope of aspect). I can’t find anything related to that on Google. This article reference is : ZHOU, Yi et al. Automatic ...
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1answer
472 views

Google Earth Engine, how to distinguish between rivers/streams and ponds/lakes in a water mask

I am trying to pull out every lake and pond in a region of SW Alaska. I have successfully identified all water features using the following code: // study area var rect = ee.Geometry.Rectangle([-168, ...
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32 views

Why is my aspect not displaying the full data?

I am trying to get the slope aspect for the altitude shown above. Can someone please advise me on why this may not be working properly?
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42 views

Calculating area of pixles for certain Aspect value per specific area?

I am using ArcGIS 10.6. I have the aspect (raster file) for the roof of buildings at the city scale. Now I want to calculate the area of each aspect group per building. I tied zonal statistics, zonal ...
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1answer
92 views

Selecting a subset of a raster, based on aspect and slope, as input to calculate area

Background I created some digital elevation models and subsequently made a 2 layer raster for each containing the calculated aspect and slope using raster::terrain. Now I want to calculate the area of ...
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1answer
105 views

Conditional Statement (CASE-WHEN) in QGIS for slope aspect

After processing a DEM with a mask to get the aspect values of some polygons I would like to create a new field classifying those values as N, NE, E, SE, S, SW, W, NW. I've written this but I can't ...
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25 views

Reading cell values of Aspect map using ArcPy? [closed]

I have generated an aspect map from a DEM using ArcGIS and I want to create a CSV file containing the cell values using the arcpy library. I have done reading raster maps using the arcpy library ...
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2answers
351 views

Why North direction is shown in red color on aspect maps?

I have been recently exposed to an aspect map that looked like this: I wonder why North-y orientations (N, NE, NW) are shown in red and orange while South-y orientations (S, SE, SW) are shown in ...
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1answer
33 views

Corine data aspect analysis in ArcGIS

I have a SRTM dataset, Corine Land Cover and have already calculated aspect. I want to know the relative proportions of exposition classes of certain landcover type. My thought was to use zonal ...
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484 views

Calculating slope and aspect from DTM lidar elevation data in ArcGIS Desktop? [closed]

I have an ASCII 2m lidar DTM file which I converted into a raster in ArcGIS with the From ASCII to Raster tool. From this DTM file I would like to calculate the slope and aspect. I have used the ...
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1answer
128 views

Calculating an “overarching” slope and aspect for each polygon of a feature class

I have a feature class containing polygons and an associated raster with elevation data. I'm looking to calculate a single slope and aspect for each polygon within the feature class. I don't want a ...
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2answers
104 views

Using Overlay Analysis (e.g., Union) with point data (point shapefile)?

Is it possible to compare a point shapefile with a DEM raster in which the Aspect tool has been applied? I am reading about Overlay Analysis but cannot find a definitive answer. The attached photo ...
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1answer
756 views

Selecting south-facing slopes with slope > 10° using ArcGIS Desktop?

I have to make a Model in the Model Builder which will select the areas with slope bigger than 10° and which are facing to the south. It should be used for environmentalist who will just insert a DEM ...
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1answer
86 views

Erratic results from filters.normal in PDAL?

Given this roof structure: I get the following output for the normalx, after using: { "type":"filters.normal", "knn":8 }, (orange to purple : -1 to 1) Comparable situation for ...
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1answer
412 views

What is the difference between Aspect and Flow Direction tools?

There are two seemingly identical Spatial Analysis tools: (1) Surface -> Aspect: Derives aspect from a raster surface. The aspect identifies the downslope direction of the maximum rate of change ...
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1answer
506 views

ENVI files (datafile +hdrfile) not displaying properly in python

I am trying to topographically correct my already atmospherically and radiometrically corrected images. To do so I need to calculate illumination conditions at the time of image acquisition. Terms in ...
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1answer
454 views

Methods in Slope, Aspect SAGA calculations

Using this algorithm in QGIS I can choose between 7 methods, the default one being by Zevenbergen & Thorne 1987. What's the difference between them and can I just use the default one without ...
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1answer
1k views

Understanding aspect units in QGIS

I created an aspect raster form a DEM raster in QGIS 2.14, and got this results: I know that the results refer to degree units , but still i don't understand how to read the map result- i mean to ...
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1answer
881 views

What is the “57.29578” that ArcGIS uses in Aspect calculation?

ArcGIS Desktop Help on How Aspect works explains the calculations used, but introduces the for me magic number of 57.29578: aspect = 57.29578 * atan2 ([dz/dy], -[dz/dx]) Where does this number come ...
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1answer
223 views

Cleaning up a raster

I recently completed a project that involved slope, aspect, and solar radiation to find optimal rooftop locations for solar panel installations. For my final map I combined the rasters that showed the ...
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165 views

Extracting cells from raster by attribute in ERDAS Imagine

I have a raster file that gives me the slope of all the hills and mountains in an area in degrees (0-90) and I need to extract all the cells which are >= 45 with an operator in the model builder. I ...
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1answer
834 views

Rotating symbols per attribute value in QGIS?

I am trying to apply a rule to rotate symbols based on the value of an attribute. I tried to copy Automatically changing the angle of a symbol in QGIS?, which is essentially my question, however it ...
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1answer
237 views

ArcGIS mean aspect of polygons from SRTM

I have a shapefile with >1200 polygons and wish to extract mean aspect (0-360) for all of them from an SRTM DEM (raster). Both are WGS84 GCS. I have found Python code to do this (here: https://geonet....
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1answer
163 views

How to correct aspect values in a North Pole Stereographic projection?

I'm working on a DEM in the Arctic region (initially in a NAD83 coordinate system) and I projected it into a North Pole Stereographic Cartesian coordinate system to compute slope and aspect. Now, ...
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143 views

Trying to Create an Aspect Map in QGIS [duplicate]

I'm trying to create an Aspect Map similar to this one: https://kingsgeocomputation.files.wordpress.com/2016/03/10sikkim-village-aspect.jpg?w=980 I have two files to work with from the start; the ...
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1answer
164 views

Information about algorithm used by Terrain models

I have calculated slope and aspect using the DEM (Terrain models) GUI in QGIS Essen. I was also able to calculate the profile and tangential curvature using the toolbox r.slope.aspect. I was wondering ...
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1answer
419 views

Merging slope angle and aspect rasters

I have created slope and aspect from a DEM layer, I reclassed both slope and aspect into categories (for example slope is now a value of 1-6) and turned them into polygon layers where each polygon has ...
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1answer
930 views

In R's raster::terrain function, which way is north?

The terrain function in R's raster package calculates slope and aspect from an elevation raster: see http://www.inside-r.org/packages/cran/raster/docs/terrain. With the unit="degrees" option, the ...
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2answers
244 views

How to find out the density or percentage of vegetation in each aspect

I am trying to find out what is controlling vegetation in an area of Saudi Arabia for my masters project and I am currently focusing on the aspect of slopes in the area. I have a DEM layer and I have ...
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0answers
129 views

GRASS 7 r.sun aspect in doubt

I'm using r.sun in GRASS 7.0.3 to determine beam irradiance at a site (~ 56N -4W). I have a DEM (a local subset of EU-DEM). I'm using r.sun in mode 2, called from GUI. Typical logging in command ...
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2answers
588 views

Is is possible to extract aspect values from raster based on vector point locations?

Looking for ideas on a workflow in QGIS: I have an Aspect raster layer and a point vector layer from the same area. Such point data represents localities of interest for a particular study. Is there ...
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162 views

Is QGIS aspect analysis description mistaken?

I've been checking the Aspect analysis tool and several sources indicate that aspect is measured from 0 to 360, starting North and going counter-clockwise. Nevertheless, I've been testing it on ...
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35 views

Problem with making raster from Aspect and wind direction data [duplicate]

I know its not correct to ask for work flow, but I am learning by doing and now I don't know how to move on. I'm trying to make new raster which will represent the facing sides of hill around a ...
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0answers
89 views

Linearising aspect in GRASS GIS

After having produced aspect of surface in GRASS GIS and being aware that GRASS GIS calculates aspect counterclockwise from east, how could we transform aspect from being a circular variable (0-360 ...
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1answer
545 views

How to get mean geographic direction of a polygon in QGIS?

I have a raster height model and would like to calculate the horizontal geographic direction (north, east, etc. - orientation) of each cell, then calculate then the mean value of all these cells in ...
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3answers
3k views

How to calculate mean aspect in circular statistics?

Measurements of angles (e.g. compass bearings, aspect) are circular in nature (e.g. 0 and 360 degrees coincide) and therefore cannot be meaningfully described by ordinary arithmetic means. I have a ...
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1answer
514 views

Using SRTM Global DEM for Aspect calculation?

I need to derive a raster representing aspect for North America (from STRM data, originally in geographic lat/long). In most projections, true north is only map north along eg the central meridian so ...