Rasters are regular grids of values, usually stored in an image-like format.
22
votes
6answers
28k views
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 ...
21
votes
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 ...
19
votes
7answers
1k 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 ...
17
votes
4answers
3k 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 ...
16
votes
3answers
809 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 ...
16
votes
3answers
2k 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 ...
16
votes
3answers
302 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 ...
16
votes
1answer
153 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
votes
4answers
826 views
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. ...
15
votes
5answers
608 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 ...
14
votes
6answers
808 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
votes
4answers
1k views
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
votes
3answers
508 views
How to deal 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 ...
13
votes
5answers
1k views
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 ...
13
votes
3answers
386 views
How to count consecutive pixel values for a set of rasters?
All,
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 ...
13
votes
3answers
246 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
votes
3answers
195 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 ...
13
votes
1answer
714 views
Good practice for generating contours from a DEM
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: ...
13
votes
3answers
8k 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 ...
12
votes
2answers
499 views
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 ...
12
votes
1answer
624 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 ...
12
votes
2answers
1k 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.
...
11
votes
4answers
8k 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 ...
11
votes
4answers
375 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 ...
11
votes
2answers
313 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
votes
3answers
223 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 ...
11
votes
1answer
328 views
QGis raster terrain analysis - The curvature filter puzzles me
I am a french Master student at university Grenoble INP, and during my master project I have worked on DEM (raster) terrain analysis. Thus, I have read the source code of several QGis-1.7.4 raster ...
11
votes
2answers
341 views
How sensitive is Landsat to atmospheric correction?
How important is it to correct Landsat for atmosphere, haze and convert DN to reflectance? What impact does it have on the results, say for many of the vegetation indices?
10
votes
4answers
684 views
Problems with NA values when reading .DEM file with R 'raster' package in Windows
I am trying to read a raster file in a .DEM format on windows using the 'raster' package in R.
I get problems with NA values, when loading the data into R in Windows 7, but I do not have the problem ...
10
votes
3answers
862 views
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 ...
10
votes
1answer
2k 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 ...
10
votes
1answer
553 views
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 ...
10
votes
5answers
1k views
How to scan large paper maps without a large format scanner?
Is there a way people have used to import a paper map as a raster without using a large format scanner. I do not want to cut my map. I'm wondering how much success people have gotten using things like ...
10
votes
4answers
364 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 ...
10
votes
3answers
589 views
Web mapping software for a huge raster time series?
I'm an ArcGIS Desktop user who is stepping into the world of web mapping for the first time. Following advice I found here on GIS.SE, I started with the free tutorials from OpenGeo.
However, I ...
10
votes
2answers
165 views
Count raster value in a bounding box (spatial extent)
I have simple question: given a bounding box, how can I count the number of specific values (say, I am interested in the number of value == 1 ) in a raster in 1) arcpy, or 2) raster package in R?
10
votes
7answers
2k views
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 ...
10
votes
1answer
362 views
Method to shade or overlay a raster map to reflect time of day and ambient light
I have a daytime raster of my study area.
I have 20+ counters in the study area that count "stuff" with a timestamp.
Using PyEphem I determined the type of ambient light for each collected data ...
9
votes
5answers
2k 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 ...
9
votes
4answers
512 views
Multicriteria Analysis : how to?
I have to do a multi-criteria analysis to answer the question : "which is the best lot to develop".
A few of the criterias are :
distance of the nearest bus stop (point layer with bus stops)
...
9
votes
2answers
573 views
Grid vs TIF vs IMG
As the title suggests both of the above three formats are raster files. In ArcGIS, apparently there's no difference between them. So what's the difference between these three formats?
9
votes
1answer
412 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 ...
9
votes
3answers
4k 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 ...
9
votes
2answers
472 views
GeoTIFFs made in GDAL don't have min/max range when loaded in Arc/QGIS
I'm creating some floating point rasters in GDAL with the GeoTIFF driver. When I load the resulting images into QGIS or Arc the default symbology puts the min at -3.40282e38 and max to 3.40282e38, so ...
9
votes
3answers
324 views
How to “clean” and vectorize a raster map?
I'd like to make use of a geological map as shown in the example below, which is only a pretty small and downsized part of the map, so editing/redrawing doesn't seem to make sense in the end.
My idea ...
9
votes
2answers
165 views
What are the advantages/disadvantages of populating a PostGIS database with Raster information?
...as opposed to keeping the rasters as locally stored GEOTIFFs?
I have a large project that will require making available approximetely 50,000, 10mb GEOTIFFs as WMS to an OpenLayers based web map. ...
9
votes
1answer
299 views
Efficient raster sampling of billions of polygons (bounding boxes)
How can a raster be computed efficiently (in Python), given a set consisting of billions of bounding boxes (read sequentially from a file), and given that the raster values for each cell should give ...
8
votes
5answers
232 views
How to ensure uniform colour for DEMs?
This is a silly question, but one I've been trying to figure out for a while. I have two Aster DEM tiles, one next to the other. How do I ensure uniform colour for both?
8
votes
7answers
4k views
How to get raster image as array in Python with ArcGIS
When starting to work with Python and ArcGIS 9.3, I assumed there would be a simple way to get a raster image into a Python array so that I can manipulate it before storing it back as another raster ...
8
votes
3answers
2k views
How to find the locations of the highest values in a raster?
Using ArcGIS 10, I have a raster where I would like to find the pixel with the maximum value in the raster and return its location (center of pixel) in decimal degrees. I would like to iterate through ...
