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

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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!) In answering someone's question today, I ...
33
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3answers
14k 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 ...
29
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3answers
29k views

How to clip a raster with vector boundaries?

I am using 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 ...
27
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7answers
3k 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 ...
27
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3answers
3k 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'd like to generate a map that highlights the magnitude of positive or negative trends in this ...
26
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3answers
7k 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 ...
25
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8answers
2k 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 ...
25
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2answers
13k 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 ...
24
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6answers
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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 ...
21
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5answers
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What is Change Detection and how I can perform 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. ...
21
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3answers
2k views

Packing Polygons within polygon

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 ...
19
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3answers
962 views

How to count consecutive pixel values for a set of rasters?

I'm using ArcGIS 10 with Spatial Analyst. I have a set of rasters (8 in total) that only every contain a 1 or a 0 for each cell. Each raster represents a different years worth of data. For arguments ...
18
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3answers
881 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 ...
17
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4answers
31k views

How do you decide what interpolation method to use for resampling raster data?

The question pretty much says it all; are there hard and fast rules about which interpolation methods are suited to each kind of raster data? Any Golden rules, rules of thumb? Good books or articles ...
17
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2answers
3k 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 ...
17
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7answers
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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 ...
16
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2answers
11k views

Clipping a 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 ...
16
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8answers
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How do I create a shapefile showing footprints of Rasters?

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 ...
16
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2answers
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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 ...
16
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3answers
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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 ...
16
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1answer
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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 ...
16
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1answer
195 views

Can we create views over a raster table in Postgis2.0?

Is it possible to create PostgreSQL views over a table that contains raster data? I have succeeded in creating the view but the entry in raster_columns is not correct (all the raster info is ...
15
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3answers
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Writing numpy array to raster file

I'm new to GIS, and I'm lost with something I feel ought to be relatively simple. I have some code that converts infrared images of Mars into thermal inertia maps, which are then stored as 2D numpy ...
15
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2answers
21k views

How can I join 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 project. ...
15
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2answers
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Generating contours from DEM using GDAL?

We have just received a large set of DEMs at work and I would like to generate contours from them. The DEMs have a resolution of 1m and a size of 1kmx1km. Output from gdalinfo: Driver: ...
15
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4answers
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Where can I find examples of fuzzy logic applications in ArcGIS?

The last ArcGIS version (10) includes two arctoolbox tools for fuzzy logic (Fuzzy Membership, and Fuzzy Overlay). Does anyone know where can I find some examples showing how they can be applied? ...
14
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5answers
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Is Hillshade option in ArcMap rubbish or is it me?

Here is a pretty pic of the raster I am using - with no effects applied - just the color ramp and historgram adjusted to show out all the relief - all be it in a very 2D way! I have a raster layer ...
14
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6answers
1k views

Creating simple image from vector data

Can anyone suggest a quick (and preferably open source) way to create an image from a shapefile. For example, I have a shapefile containing parcel boundaries, I want to create a png file depicting ...
14
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3answers
498 views

Which CRS would you use to georeference historical world maps?

Which CRS would you recommend to georeference historical world maps like the ones in the London Geographical Institute - The Peoples Atlas - 1920, e.g. The map displays a lat/lon grid which I would ...
14
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3answers
443 views

Is it possible to use symbols instead of colours to visualise raster cell values?

I have a raster image (GeoTIFF) with integer values. I know how to visualise raster values in QGIS using colormaps or similar, but I would like to assign symbols to each colour value instead - just ...
13
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4answers
636 views

When should I be calling a 'rectangular grid of pixels' a raster or an image?

Reading through GIS literature, it sometimes feels that authors use the two terms with a specific meaning in mind. I always treat the terms interchangeably. Am I wrong? Read the first line in the ...
13
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2answers
4k views

How to smooth/interpolate a raster in python using GDAL?

This is my first post so please feel free to critique where necessary. Background: I am developing in Python and using GDAL from OSGEO to manipulate and interact with rasters and shapefiles. ...
13
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2answers
4k views

How to count and rasterize polygon overlaps in ArcGIS Desktop?

How do you take a vector layer with overlapping polygons and turn it into a raster where each cell counts the number of polygons containing that cell? We are looking at polygons of fire burn areas ...
13
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3answers
34k 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 ...
13
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5answers
841 views

Dikes extraction from DEM

I do have DEM of 1x1 meter and original LiDAR point cloud in .las, that DEM is made of. I need to extract river dikes (highest points of the dikes) to vector feature (point, polyline). Any idea for ...
13
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5answers
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How to perform Raster Reclassification in QGIS?

Is there a way to do reclassify a raster image to Qgis? In Arcgis you can do that in Spatial analyst Tools→Reclass→Reclassify Any ideas?
13
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1answer
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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 ...
13
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4answers
10k views

Loading a raster into a PostGIS 2.0 database on Windows

I'm trying to figure out how to load a raster into a PostGIS2.0 database (I have asked previous questions on this topic here and here). I am trying to use the raster2pgsql.exe program provided with ...
12
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9answers
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Get boundary of raster image as polygon in ArcGIS Desktop?

I have a rectangular raster image in ArcGIS. My question is: 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 ...
12
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7answers
10k views

Extract raster values at points

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.
12
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5answers
5k views

Get Raster Values from a Polygon Overlay in Opensource GIS Solutions

I have two layers. A polygon-shape-layer with many tiles and a raster-layer containing CORINE 2006 land cover with many categories in a colourmap. I want to obtain for each polygon in the shapelayer a ...
12
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6answers
9k 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 pic): ...
12
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1answer
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Random sampling of raster using R

Is there a straightforward way of randomly sampling a raster so that the output of the process is a raster? I'm using an example that I found on the r-sig-geo list and I have also tried the ...
12
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3answers
331 views

What practices are available for modelling land suitability?

I currently use a "classic" raster based approach of dividing a study area into cells. All input layers are converted to rasters at the same cell resolution and given a suitability rating. A final ...
12
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3answers
27k views

How to convert a vector layer to raster?

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 ...
12
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2answers
3k 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 ...
12
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0answers
261 views

Frequency of overlapping isochrones with map algebra in PostGIS

I have a table of polygons representing travel time isochrones on particular days. For each origin point, there are five isochrone geometries (stored in separate rows). For each origin point, I want ...
11
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2answers
585 views

Converting ascii windspeed files to rasters

I have been trying to convert windspeed files to rasters without success. It was discussed in an Arcgis forum which I followed. This involved replacing semi-colons with spaces and adding a header. I ...
11
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3answers
9k views

How to fully load a 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 ...
11
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2answers
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How to calculate average slope in a grid?

This is actually a two part question: Which methods are there to calculate average slope by unit (say km²) for a given area? Are there any special requirements on the data - like additional ...