Rasters are regular grids of values, usually stored in an image-like format.
8
votes
3answers
924 views
Best method to aggregate 1m DEM mosaic to 10m DEM
I have a mosaic of a 1m LiDar derived DEM. I need to output a subset of the data as a 10m DEM. I am currently using the aggregate tool in ARCGIS 10 to produce a mean value for each new 10m pixel. ...
8
votes
2answers
356 views
How to reclassify a very large land cover dataset?
Consider the NLCD2001 Land Cover dataset for Alaska (download link). I need to reclassify this dataset so that only pixels of value 41, 42, and 43 are preserved; all other pixel values should become ...
8
votes
2answers
414 views
Extract the area of a DEM above where 60% of the region lies?
I have a DEM of a mountainous region. I'd like to extract the areas of the DEM above which 60% of the total DEM area lies. So, essentially I'd like to extract the areas representing upper portions of ...
8
votes
3answers
573 views
Best way to manage large number of geoTiff rasters
I have around 2-3000 1-bit geoTiffs of size 11000x9400. Color 0 should be transparent, and QGis gets it wrong in the first place, so I used a .vrt file to set all the parameters in one single place.
...
8
votes
1answer
469 views
How to apply a Majority filter in GRASS GIS?
I was wondering if someone could help me write a majority filter for GRASS GIS. I have this map (see below) which I need to run a filter over to make the red areas a bit more dominant. I know I can ...
8
votes
2answers
237 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 ...
8
votes
2answers
518 views
How to convert a vector boundary to a raster map?
I need to output a PNG file of a raster map overlayed with boundaries present in a vector map. The problem is, the r.out.png script only exports a raster map. My boundaries are in a vector format. ...
8
votes
2answers
2k views
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?
8
votes
1answer
113 views
What is some theory on the number of GCP when georeferencing?
Just wondering, is it always better to have more than 3 GCPs? Should the GCPs be spread out evenly? Where can I find some general resources on the theory of this? Other than trial an error, which ...
8
votes
1answer
321 views
How to make a new raster using con() script in Python?
I'm new to Python and have been trying to code a raster calculator style script. Basically, I want to convert a raster that has values 0 to -10,000 into a raster that is populated by 1s between ...
8
votes
1answer
255 views
How should I manage PostGIS Raster data with different projections?
I have a requirement to store and manage archaeological geophysics data that is collected as a rectangular array of samples -- a raster image.
Each raster will usually 20x20 or 30x30 floating-point ...
8
votes
3answers
792 views
How can I mosaic images in ArcMap without it affecting the colour?
This is 4 images (NE, SE, NW, SW) sections of imagery. They have some overlap between them.
Working with 1m 3-band orthoimagery.
Different parts are sometime flown at different times/sources hence ...
8
votes
4answers
301 views
Identify corrupt shapefiles or rasters via Python or ArcObjects
I'm interested in a way to identify rasters (e.g., ESRI GRID format) or shapefiles that are corrupt that would prevent them from being used in an analysis tool. I have a large number in structured ...
8
votes
2answers
398 views
Scriptable alternative to ArcScan (particularly vectorising lines within tolerances)
Sadly the answer to this question suggests that it is not possible to script ArcScan from within a python script.
Therefore, does anyone know of any alternatives to ArcScan (either within ArcGIS, or ...
8
votes
1answer
279 views
What is the correct way to convert a USGS Orthoimage from WorldImage format to tiled GeoTiff for GeoServer?
USGS provides different resolution orthoimage quadrangles in the WorldImage format (*.tif with an accompanying *.tfw world file). Some of these quadrangles can be used by GeoServer (2.1.0 - 2.1.2) by ...
7
votes
3answers
476 views
GDAL and Python: How to get coordinates for all cells having a specific value?
I've got an Arc/Info Binary Grid---specifically, an ArcGIS flow accumulation raster---and I'd like to identify all cells having a specific value (or in a range of values). Ultimately, I'd like a ...
7
votes
2answers
363 views
Resample binary raster to give *proportion* within new cell window
I would like to go from a binary raster of forest/non-forest at 30m resolution to a raster at 240m resolution with the value of each cell being the proportion of that cell forested - i.e. the data ...
7
votes
2answers
173 views
How to create a solar intensity map for a garden plot?
I'm interested in creating a raster surface that depicts the average solar intensity per unit area for a small garden plot. I imagine the inputs into the model would be the following:
Plot ...
7
votes
3answers
438 views
Creating raster or vector raster from DEM point file?
i have a point shape of 75.000 elevation points in a regular 5 m grid.
We now want to create a polygon grid with the elevation points as "centroids".
Unfortunately, all attempts to do so fail:
I ...
7
votes
5answers
5k views
Get boundary of raster image as polygon in ArcGIS 10
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 ...
7
votes
4answers
3k views
How can I export raster data from Arcmap to an R *.grd file format?
I want to work with raster data in R, but I have problems exporting my raster dataset from ArcMap. By "export data"/GRID I get a file with an *.aux extension. What I need is *.grd.
Can anybody help ...
7
votes
1answer
225 views
How do I randomly alter a raster map of habitat types?
I have a raster of habitat types for a specific area in Scotland. I need to create future habitat scenarios with changes in habitat to assess the population viability of a bird species.
For example, ...
7
votes
2answers
2k views
Difference between Geoserver stores: ImageMosaic, WorldImage, ImagePyramid
What are the differences between the Geoserver stores ImageMosaic, WorldImage, and ImagePyramid? I noticed that ImagePyramid is no longer included in the latest Geoserver. Is one of these more ...
7
votes
7answers
602 views
seeking “Available Sky” implementations
I'm looking for implementations of an algorithm called "Available Sky". ArcGIS (Spatial Analyst or GRID) is preferred, but solutions in GDAL, SAGA GIS or others are perfectly acceptable.
The ...
7
votes
2answers
195 views
How to count and rasterize polygon overlaps in ArcGIS?
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 ...
7
votes
1answer
240 views
Reduce extent of raster processing
I need to reduce the processing extent of my raster by some sort of automatic procedure in python. Currently the borders of the dataset I've been using has anomalies (due to the classification of the ...
7
votes
3answers
388 views
How do I create a raster randomly choosing a cell value from 2 or more overlapping rasters?
I'm using Arc 10. I want it to combine multiple rasters into one, always choosing randomly from the values of overlapping cells. I have an image that may explain this better:
7
votes
1answer
1k 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 ...
7
votes
2answers
691 views
PostGIS raster value of a lat/lon point
I have a tiff raster in my PostGIS 2.0 database. I want to get the value of the raster at a specified lat/lon point.
I have:
postgresql-9.1
postgis-2.0-svn with raster support
a raster imported ...
7
votes
1answer
634 views
GRASS - Will r.to.vect work on this scanned map?
Total GRASS noob here. I have several very large hand contoured maps to digitize, and this thread intrigues me. In the past I have spent hours upon hours digitizing these maps and revisions in ArcMap. ...
7
votes
3answers
1k views
Make the nodata area of a resampled orthophoto overview white?
I have a set of orthophoto images which are each fully filled with data, but when placed together the coverage does not form a rectangle so there are nodata areas.
In MapGuide, I need to be able to ...
7
votes
2answers
246 views
Python, GDAL and building raster attribute tables
I have an integer raster for which I would like to build a raster attribute table using Python and GDAL. I can create a GDAL raster attribute table in Python as follows:
>>> rat = ...
7
votes
1answer
546 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?
7
votes
1answer
651 views
Is there a fast way to copy large raster datasets between File Geodatabases?
Why does it take so long to copy a large raster dataset from one file geodatabase to another? I can copy the entire database in windows explorer in minutes but copying a single raster in ArcCatalog ...
7
votes
1answer
280 views
What are the rules that the Gdal rasterize function follows to allocate a value to a cell?
How does the rasterize tool decide which value to represent when a cell covers an area which inclueds different values? I need it in this case for polygons but would like to know for lines and points ...
7
votes
2answers
129 views
Using ArcGIS to filter cells where 7 or 8 of the neighbors are different
I have land cover data that I would like to clean using some generalization tools. Majority filter does almost exactly what I want, but is missing one key option. Majority filter allows you to change ...
7
votes
1answer
108 views
How to improve the display of color images?
I've found some really nice color ramps for portraying rasters, but in ArcGIS and QGIS, they don't seem to be easily usable for a finished product because their complexity causes obvious steps rather ...
7
votes
1answer
136 views
Calculating distance from points to different class in raster
I am looking for some advice on how to calculate the distance from a point to a different class of a raster. Specifically, I have observations (points) of animal use overlaid on land cover data. For ...
7
votes
1answer
190 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 ...
7
votes
2answers
106 views
How to perform enhancement operations on an satellite imagery in QGIS?
I am a new user of QGIS please suggest how to perform image enhancement operations on an satellite imagery like ratioing, contrast stretching, edge engancement, filtering etc. in QGIS?
7
votes
2answers
724 views
Poor image quality of raster pyramid files in ArcGIS (no anti-aliasing)
There are several GeoTIFF files (size ~7000x7000 px) which I try to open in ArcGIS Desktop 10.0. I have already created raster pyramids for them (.ovr files) using geoprocessing tool but their quality ...
7
votes
2answers
839 views
Intersecting a raster with a polygon using PostGIS - artefact error
I'm using PostGIS2.0 to do some raster/polygon intersections. I'm having difficulty understanding which operation I should use, and what the quickest way of performing this is. My problem is as ...
7
votes
1answer
421 views
How can I change the class of one pixel in a classified image?
I have a classified image (I did it in ERDAS) with six categories. There are some misclassified pixels (especially high-density urban category). Is there any way that I can choose one pixel and then ...
7
votes
2answers
141 views
How to remove long linear strips from polygons?
I have a polygon layer representing impervious land cover. This was taken from a land cover raster dataset. The impervious data represents all impervious surface that is not buildings or roads. I ...
7
votes
1answer
337 views
How to grid unevenly sampled categorical data?
I am looking for a method for gridding categorical data. I have extracted from nautical charts and field sheets a collection of points specifying the nature of the surface of the bottom of the ocean. ...
7
votes
1answer
188 views
Looking for US National Grid to Lon/Lat Converter in Python, C, or C++
I see here that there is Fortran source code for going from USNG to lon/lat: http://www.ngs.noaa.gov/PC_PROD/USNG/
Is there some python or C/C++ code that does the same?
My understanding that this ...
6
votes
7answers
2k 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.
6
votes
6answers
7k views
How to get X Y coordinates and cell value of each pixel in a raster using Python?
I’m really new to Python and I would like to know whether there is a quick method to get cell values of a raster pixel by pixel and the coordinates (map X Y coordinate of centre of each pixel) using ...
6
votes
2answers
133 views
Breaking apart a polygon layer by unique values, creating many new layers
I have a large dataset of habitat information that I need to calculate distances from animal locations to the closest polygon of each habitat type. The way to do this, that I understand, would be to ...
6
votes
3answers
3k views
Clipping a raster using a polyline or polygon
I have a large raster created from values that cover the whole United States and Alaska which are both polygon and polyline features, this raster was caluclated using Spatial Analyst IDW ...
