Questions tagged [raster]

Raster is a data format consisting of regular grids of values, usually stored in an image-like format.

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Clipping raster with vector boundaries using QGIS

In QGIS I would like to clip a raster precipitation layer using an admin boundary layer that is vector data. However the Geoprocessing tools seem to be usable only for vector data. How can I clip this ...
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55 votes
3 answers
21k views

What is Lanczos resampling useful for in a spatial context?

GDAL includes a resampling method beyond the normal mix of nearest neighbor, bilinear, cubic and splines: "Lanczos windowed sinc resampling". I understand that its a convolution filter, but unlike ...
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48 votes
8 answers
52k views

Using continuous color band for raster legend in QGIS composer legend?

I'm looking for a way to insert continuous colour legend for a raster layer. I managed to create discrete symbols with values along the bar, but I would like to have a continuous bar with some values ...
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48 votes
5 answers
40k views

What raster smoothing/generalization tools are available?

I have a DEM that I would like to smooth or generalize to remove topographic extremes (chop off peaks and fill-in valleys). Ideally, I would also like to have control over the radius or level of "...
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47 votes
7 answers
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What are Raster and Vector data in GIS and when to use?

What are raster and vector data in the GIS context? In general terms what applications, processes, or analysis are each suited for? (and not suited for!) Does anyone have some small, concise, ...
44 votes
2 answers
50k views

How can I convert data in the form of lat, lon, value into a raster file using R?

I have a data set of values over a km grid in the continental U.S. The columns are "latitude", "longitude", and "observation", e.g.: "lat" "lon" "yield" 25.567 -120.347 3.6 25.832 -120....
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44 votes
4 answers
62k views

Deciding what interpolation method to use for resampling raster data?

Are there hard and fast rules about which interpolation methods are suited to each kind of raster data?
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  • 595
39 votes
6 answers
26k views

Increasing speed of crop, mask, & extract raster by many polygons in R?

I'm extracting the area and percent cover of different land use types from a raster based on several thousand polygon boundaries. I've found that the extract function works much faster if I iterate ...
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38 votes
5 answers
59k views

Writing numpy array to raster file

I'm new to GIS. I have some code that converts infrared images of Mars into thermal inertia maps, which are then stored as 2D numpy arrays. I've been saving these maps as hdf5 files but I'd really ...
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38 votes
7 answers
54k views

Performing Raster Reclassification in QGIS

Is there a way to perform a reclassify of a raster image in QGIS? In ArcGIS Desktop you can do that in Spatial analyst Tools→Reclass→Reclassify
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38 votes
8 answers
30k views

Creating shapefile showing footprints of Rasters? [closed]

I have around 1,000 satellite images in tiff format, and I want to create a shapefile which will serve as an index to the rasters. This is something similar to a raster catalog, but I do not want to ...
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37 votes
2 answers
79k views

Clipping raster in R

I am building a map for the northeastern U.S.A. The map background needs to be either an altitude map or a mean annual temperature map. I have two rasters from Worldclim.org which give me these ...
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36 votes
5 answers
126k views

Extract Raster Value into Polygon Attribute

I have Raster Data for a State which has Elevation Data in its pixels. I also have Vector layer which has the 300 divisions of State. what I need is, I want to get the average elevation value of ...
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34 votes
13 answers
100k views

Getting boundary of raster image as polygon in ArcMap

I have a rectangular raster image in ArcMap. How can I produce a polygon which is just the extent of the raster image? That is, I want to have a polygon layer with a single quadrilateral which is the ...
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34 votes
4 answers
62k views

Fully load raster into a numpy array?

I have been trying to check my filters on DEM raster for pattern recognition and it is always resulting in missing last rows and columns(like..20). I have tried with PIL library, image load. Then with ...
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  • 787
34 votes
3 answers
7k views

How to represent trend over time?

I have a time series of rasters where the cells of each raster represents some value at a certain time. I would like to generate a map that highlights the magnitude of positive or negative trends in ...
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33 votes
7 answers
4k views

Work flow for georeferencing imagery using open source tools?

Does anyone have a recommendation for a work flow for georeferencing high resolution aerial photography using open source tools? Comparison of user friendliness and robustness between Quantum GIS ...
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  • 493
33 votes
1 answer
40k views

Raster legend in R: how to colour specific values?

I have an elevation model plotted in R r <- raster("example.dem") plot(r, col = topo.colors(20)) Some of the values are below sea level (0), and I'd like to have those display in red. How can I ...
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31 votes
6 answers
4k views

How to buffer raster pixels by their values?

The pixels to the left represent tree locations and their associated crown radii (i.e. pixel values ranging from 2 - 5). I would like to buffer these raster pixels by their crown radius value. The ...
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30 votes
6 answers
17k views

Splitting raster into smaller chunks using GDAL?

I have a raster (USGS DEM actually) and I need to split it up into smaller chunks like the image below shows. That was accomplished in ArcGIS 10.0 using the Split Raster tool. I would like a FOSS ...
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30 votes
5 answers
14k views

Calculating terrain Curvature in QGIS

I have an elevation raster and I would like to get some basic terrain variables, such as slope, ruggedness, aspect or curvature. The problem is that I don't seem to have the possibility to calculate ...
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30 votes
2 answers
65k views

Joining several raster files using QGIS?

I'm new to QGIS. How can I combine multiple raster layers into one layer? The raster images are of different areas with very little overlap. The goal is to bring numerous town plats into one ...
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29 votes
8 answers
3k views

What raster-based GIS systems really work?

Raster GISes like GRASS, ArcGIS/Spatial Analyst, and Idrisi can perform a rich set of data processing and analytical procedures loosely known as "map algebra." In today's computing environment it is ...
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28 votes
12 answers
84k views

Extracting raster values at points using Open Source GIS?

How can I extract values from a raster by points? I prefer not in Arcgis. I prefer in Qgis or Mapwindow or other open source gis.
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28 votes
7 answers
8k views

Speed of various raster data formats

I'm having trouble locating any discussion or comparative benchmarking of different raster file formats (e.g., for use in data analysis in R). Does anybody have any insight into why particular formats ...
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28 votes
4 answers
85k views

Converting vector layer to raster using QGIS?

In qgis in the raster menu there is an item "convert vector to raster". This behaves strangely - I do not understand how it is supposed to work. I can select a vector file, an attribute and an ...
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  • 845
27 votes
3 answers
50k views

Resampling GeoTIFF images to same resolution using QGIS

I have two geotiff images that I would like to resample the same resolution. If I use ArcGIS Desktop this is easy to do but how do I do this using QGIS?
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26 votes
6 answers
16k views

What is Change Detection and performing such analysis with open source tools?

From wikipedia page: Change detection for GIS (geographical information systems) is a process that measures how the attributes of a particular area have changed between two or more time periods. ...
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26 votes
3 answers
8k views

What resampling technique should be used when projecting aerial photos?

I'm doing some time-intensive projecting of aerial photos, and I'm curious - what resampling technique is best to use on aerial photos? In ArcMap, my options are NEAREST, BILINEAR, CUBIC, and MAJORITY....
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26 votes
3 answers
31k views

Differences between Raster Dataset, Raster Catalog, and Raster Mosaic

I have about 40 scanned, colorful Geology maps that are GeoTiffs. I want to bring them into an Esri FileGeodatabase to lower their size, combine them as one and display them with a mostly transparent ...
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26 votes
3 answers
4k views

Packing Polygons within polygon using ArcGIS Desktop?

I have a Boolean raster. In the grey areas of the raster I would like to fit a given size polygon within a contiguous extent. Basically, I have an irregular polygon, and i would like to "fit" a ...
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  • 925
25 votes
1 answer
52k views

How to assign CRS to RasterLayer in R

I have a layer with coord. ref. : NA. How can I assign coord. ref. : +proj=longlat +datum=WGS84 +no_defs +ellps=WGS84 +towgs84=0,0,0 to coord. ref. : NA? class : RasterLayer dimensions : 127,...
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  • 821
25 votes
4 answers
23k views

Rasterfile clipping error: Cannot compute bounding box of cutline

I have a raster file and want to clip it, a vector file is supposed to be the mask layer. I use the most obvious method (Raster->Extraction->Clipper). No matter what I do, I get this error (see ...
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  • 2,190
23 votes
3 answers
13k views

Smoothing/interpolating raster in Python using GDAL?

I am developing in Python and using GDAL from OSGEO to manipulate and interact with rasters and shapefiles. I want to take a shapefile that has point features and interpolate it into a surface raster....
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  • 607
23 votes
1 answer
5k views

Are there any general rules of thumb for selecting a transformation for Georeferencing?

There are several transformations that can be used when georeferencing a raster: 1st order Polynomial (affine) 2nd order Polynomial 3rd order Polynomial Spline... etc Are there any specific rules or ...
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23 votes
2 answers
43k views

Understanding ESRI's .asc file

Reading the ArcGIS help: Supported raster dataset file formats, I read that ASCII Grid file types are addressed with the singular file extension .asc for both 16 bit signed-integer (for discrete data) ...
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  • 9,881
23 votes
5 answers
23k views

Extracting raster values and creating new raster in QGIS?

I want to extract certain values of a raster image in order to create a new raster which then should only contain the extracted/chosen values. How to do this in QGIS?
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23 votes
3 answers
16k views

Accessing raster attribute table in QGIS?

I have some Python code that makes Raster Attribute Tables for GeoTiffs using GDAL. In ArcGIS I can see these attribute tables fine and they behave how I like (as classifications) but in QGIS the ...
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  • 1,530
23 votes
1 answer
1k views

Displaying numbers of single band raster layer in QGIS without additional vector layer?

I wonder if there is a raster symbolizer in QGIS with a label option, that renders the cell values as labels of single band raster layer, a scalar field. The standard raster symbolizer dialog in QGIS ...
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  • 3,463
23 votes
1 answer
3k views

Clustering of multiple raster layers to create sub-regions using QGIS?

I'm attempting to create n sub-regions from a polygon based on a cluster analysis of a bunch of overlapping raster layers (physical layers, eg: depth, currents, waves). Currently, I can create a ...
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  • 231
22 votes
4 answers
25k views

Layer stacking rasters in QGIS?

I have some multi-spectral data, where the individual bands are separate Raster files. How do I layer stack these rasters so that I get one raster with 3 bands instead of 3 different rasters? This ...
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22 votes
8 answers
21k views

Modifying single Pixel values in QGIS?

I would like to modify a raster (pixel values) in QGIS. The plugins "value tools" can easily provide me with the value of the pixel of my raster. However I don't know how to modify it. I have found ...
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  • 861
22 votes
5 answers
17k views

How to efficiently access files with GDAL from an S3 bucket using VSIS3?

So, GDAL has recently added a new feature that allows random reading of S3 bucket files. I am looking to crop GDAL images from multiple tiles of an image without having to download the whole file. I'...
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  • 459
22 votes
3 answers
13k views

Performing Raster Noise Reduction and Edge Smoothing?

I have a raster image like this I want to delete the isolated noise point and smooth the edge (say the white single points, and I want the edges of the entity look smooth). How can I do this in ...
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  • 2,195
22 votes
1 answer
10k views

numpy array to GTiff using rasterio without source raster

I have a numpy array that represents rasterized data from a LiDAR point cloud. For example: import numpy as np import rasterio arr = np.random.randint(5, size = (100, 100)) I know information about ...
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  • 1,034
22 votes
3 answers
1k views

Dealing with bridges and tunnels when modeling raster least cost paths?

I'm currently using ArcGIS 10 Spatial Analyst's Cost Path tool to model pedestrian routes. I have sidewalks, fences, buildings and a ton of pedestrian scale features, all combined into a cost surface ...
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  • 221
21 votes
1 answer
370k views

What is the difference between Vector and Raster data models? [duplicate]

From: http://support.esri.com/en/knowledgebase/GISDictionary/term/vector%20data%20model vector data model: [data models] A representation of the world using points, lines, and polygons. Vector models ...
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21 votes
4 answers
9k views

What to do with -3.4e+38 nodata values?

I am trying to process some bioclimatic raster files, such as can be downloaded from http://www.worldclim.org/current (bioclim set). They seem to have nodata values set to -3.4e+38 according to QGIS (...
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20 votes
2 answers
17k views

How to extract pixel value counts from a raster in QGIS?

How does one go about obtaining a summary of the counts of cell values within a raster in QGIS? I know QGIS is doing this, in order to provide the summary statistics and histogram in the properties of ...
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  • 303
20 votes
1 answer
13k views

Calculating distance to points in QGIS

Is there a way of calculating the distance to the nearest points in QGIS? In ArcGIS Desktop there is a function called Euclidean Distance, which can take an input vector or raster, and generate a ...
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