Tagged Questions

Rasters are regular grids of values, usually stored in an image-like format.

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6
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2answers
627 views

How to change null values raster values to 0 in QGIS?

I need help... I'm having problems with QGIS. I have some rasters that appear to have null values, even though I reclassified them to obtain a boolean raster :( How can I change the NULL values to 0?
6
votes
3answers
516 views

How can I select vector features that overlay raster in arcpy?

I have two datasets: point feature class and raster (stored in file geodatabase). The spatial extent of the raster is smaller than the point dataset. Is there a way I could select (or create new, ...
6
votes
2answers
3k 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. ...
6
votes
3answers
2k views

Simple Question: Raster from ArcGIS to Geoserver

we have a couple raster files which could be open in ArcGIS. They come with the extension of .aux and .rrd and they are the GRID file format from ESRI. We want to put them on Geoserver to overlay them ...
6
votes
5answers
792 views

Is there a way to clip an image with the basic ArcView package (9.3)?

Is there a way to trim a geo-referenced air photo to an irregularly shaped boundary? I tried the clip tool shown in my attachment, but it didn't work. It looks as though the output extent field ...
6
votes
2answers
193 views

How to simply label raster cells?

I think the title says everything but: I want to generate a small sample raster (eg. euclidean distance or cost distance) to explain the method of cost-distance analysis, and I'd like to label the ...
6
votes
4answers
2k views

How to install “1-band color raster color table”?

I would like to use the "1-band raster colour table" extension. I'm using QGIS Wroclaw 1.7.4. In the plugin installer I can't find this extension, even I quote for third party extensions thing. Does ...
6
votes
3answers
1k views

R: Download a large DEM, change projection, and adjust to smaller scale

This is a process that takes just a few seconds in GIS software. My attempt to do it in R uses a large amount of memory then fails. Is there something wrong in my code, or is this just something R ...
6
votes
3answers
2k views

How to calculate raster statistics for polygons?

how can I calculate sums, averages etc of raster-points (multi-band) per polygon of a vector-layer. I was told that this is called "zonal statistics". I tried that with QGIS first. There is a way to ...
6
votes
3answers
1k views

How do I get a hypsometric curve from my elevation data?

I have my elevation data but can't make an attribute table from it and so I'm not sure how to get any of that data into a table in order to make a hypsometric curve. Please help.
6
votes
2answers
163 views

Extracting roads out of Landsat raster images

For a study into the expansion of road networks in the rainforest I am trying to extract roads out of Landsat images. We already have sharp and cloud-free composites on which the roads are clearly ...
6
votes
2answers
859 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 ...
6
votes
2answers
580 views

creating a raster of the residuals of a regression between two rasters

I am trying to create a raster of the residuals of a regression between two rasters. i.e. I would like to carry out a regression of one raster against another of the same extent and plot the residual ...
6
votes
1answer
506 views

FOSS method to split raster into smaller chunks

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 ...
6
votes
3answers
748 views

How to find the elevation differences between adjacent pixels in ArcGIS?

Is there a way to determine what the difference in elevation is between two adjacent pixels? I am using an SRTM DEM to map faults. I am using the vertical error (>16m) as a criterion for the ...
6
votes
2answers
455 views

Raster to Vector

I want to map out moisture availability using satellite image but I do not know how to convert the raster image to a thematic map with limiting boundaries like state boundaries. I am using ArcGIS 9.3 ...
6
votes
1answer
354 views

How to modify the colors of a raster map to use only one color in varying shades?

I have a raster map in GRASS containing elevation values. I want to display the elevation values in only one color (specificaly blue) but in varying shades of blue. I tried the options in r.colors, ...
6
votes
3answers
165 views

How to efficiently read and reclassify many rasters in R

I've been tasked to create a suitability analysis of wave conditions in the Gulf of Mexico. I have 2 thousand or so raster files that are about 8 MB each (2438 columns, 1749 rows, 1km cell size). ...
6
votes
1answer
77 views

weighted mean across rasters in R

I have 2 rasters. One raster (bio1) contains temperature information across a continent. The other (sp) contains, for each cell, a probability of occurrence for a species. I would like to calculate ...
6
votes
1answer
167 views

Calculating “relative slope” per Mora-Vahrson method in ArcGIS

I'm a longtime lurker who finally decided to register on the forum (in no way driven by my need to have a certain question answered, of course...). I was contacted by a colleague asking for help ...
6
votes
3answers
810 views

Raster: How to get elevation at lat/long using python?

I was wondering if anyone has some experience in getting elevation data from a raster without using ArcGIS, but rather get the information as a python list or dict? I get my XY data as a list of ...
6
votes
1answer
92 views

How to reclassify raster data by their sign?

I want to do the following: I have two data raster sets with different units and values. One results from measured metric data, the other from modelled grid values. What I want to compare is simply ...
6
votes
3answers
407 views

How to make transparent the background of a topographic map in QGis 1.8.0?

I'm starting to use QGis 1.8.0. I have a raster topographic map, i.e. white background and black contour lines, houses, roads and so on. I want to make transparent the white background, so if I ...
6
votes
1answer
273 views

Normalizing and adding kernel density rasters

I have 4 years of road kill data for one road, though each year has a different sample time frame (i.e. May-June vs. April-October) and therefore each year has a different number of surveys and totals ...
6
votes
2answers
301 views

calculate area of vegetations in a raster file

How do I calculate area of several vegetation types in a raster (.img file type) image. They are color coded. Am using QGIS (1.8.0) and ERDAS 9.2.
6
votes
1answer
111 views

Is there a difference between projecting shapefiles then rasterizing & rasterizing shapefiles then projecting?

I currently have a project where I rasterize shapefiles into simple presence/absence (1 & 0) rasters and then add each one to a running total to create a total richness raster at the end. The ...
6
votes
3answers
544 views

How to sum up pixel values in QGIS?

I need to know the value of the sum of all pixels in a raster. However, in the Statistics section of the Metadata tab in Properties, under Sum of All Cells it always indicates 0.00. I have tried with ...
6
votes
1answer
536 views

Creating a mask with transparent pixels in python

I have a geotiff image with pixel intensities ranging between certain values. Lets say bewteen -2 and 2 (the image is normalized). I have a certain threshold which interests me, lets sat 1. I would ...
6
votes
1answer
154 views

Finding largest number of observations within a given radius

I have the following problem: Given the location of insured properties (say houses with fire insurance), i have to find the largest sum of insured values which fit into a 300m radius. Now, my first ...
6
votes
1answer
336 views

In QGIS, how do I remove a band from a raster?

When I process a raster in QGIS it creates a second band. It appears that band has no useful data. I like to use the Raster Colours Tool and it will not accept a raster with anything more than on ...
6
votes
1answer
730 views

QGIS WKT Raster Plugin error, what does this mean?

I have been playing with the WKT Raster plugin. I have installed the WKT Raster experimental binaries in PostGIS successfully and followed the instructions in the read me to the letter. When i am in ...
6
votes
1answer
123 views

Raster aggregation in ArcGIS

I'd like to aggregate a raster from 1m to 6m in ArcGIS with a custom rule. For example, each cell value of aggregated raster = mean value of 5 highest cell values from 36 aggregated values. How do I ...
6
votes
2answers
2k views

How to extract road and building features from raster data?

I work with raster data and my task is to digitize a big image. This consumes much time just for digitizing roads and buildings! I'm looking for tools to simplify working on raster data to digitize ...
6
votes
1answer
282 views

Smoothing raster features into polygon

I have raster data representing urbanized areas, which I'd like to trace and convert to a polygon. Using ArcMap's Raster to Polygon tool, I'm able to get something close to that. Unsimplified: ...
6
votes
2answers
218 views

Confidence interval from raster data

I have raster data that represents a probability distribution, i.e. each cell has a probability value (in my case the probability that an animal may be found in the cell), and all the cells add up to ...
6
votes
3answers
721 views

Converting point data into a weighted raster

I am completely re-writing my question as i think it was quite confusing before: I have a number of different points, each point has a -z value. I need to create some sort of raster or a series of ...
6
votes
1answer
453 views

Is there a way to get the percentage of different landuse types upstream of a given point?

I'm a fairly novice GIS user and know just enough to get in trouble in a lot of cases. I am trying to look at the connection between several measured parameters at a few hundred stations along ...
6
votes
1answer
668 views

ArcGIS 10: Adjust custom grid intervals based on map scale?

I am preparing a pmf which includes a custom grid overlay. To clarify: a custom grid overlay is marginalia, not a feature class with geometry (so a scale dependecy inside a layer won't work). The ...
6
votes
1answer
99 views

Automatic detection of breaklines with a DEM

Breaklines are very useful for describing a terrain - for example to build an exact TIN. My question is, how to extract these breaklines from a given DEM. I calculated the curvature (vertical) - ...
5
votes
2answers
945 views

How to build an artificial 'dam' across a river?

I have a DEM. Created all files related to watershed including accumulation, direction, streams etc... I'm stuck creating a dam. I request you to please let me know how to build an artificial 'dam' ...
5
votes
7answers
990 views

how to overlay shapefile and raster?

I have a shapefile with polygons. And I have a global raster file. I want to overlay the shapefile's polygons onto the raster grid and calculate the mean raster value for each polygon. How can I do ...
5
votes
5answers
283 views

How to find the minimum extent of a given pixel value of a raster?

I am wondering if there is a way to find the minimum bounding extent for a raster with a particular value. I clipped a raster from a global image and the extent is set as the global extent with a lot ...
5
votes
4answers
550 views

Find the best path along raster

I've just posted a question to StackOverflow about the best way to go about finding the best path on the raster below (where whiter pixels are 'better'), but have realised that it might actually be ...
5
votes
2answers
635 views

How do I layer stack 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 ...
5
votes
3answers
965 views

resize image resolution from 1000 m to 250 m

I'm beginner of ARCGIS and RS. I have many problems with the procedure. One of them is I have NDVI images and Soil map. Both are at the different resolution: NDVI is 250 m. soil map is 1000 m. So I ...
5
votes
2answers
339 views

Disaggregating aggregate GIS data using remote sensing

I haven't really done much with remote sensing imagery. I have census data for an area, and a TIFF raster image of the area. I'm sure this is possible, is there a simple way to disaggregate the ...
5
votes
3answers
2k views

Insert Raster to MXD using arcpy.mapping (ArcGIS 10)

What i want to do seems simple. But again i can't even find a workaround... I have got a lot of Raster-files (ESRI-GRID) which i need to insert into a layout mxd-file and then export the map to ...
5
votes
2answers
571 views

Moving raster to different mapset GRASS GIS

I have a raster DEM that I created in one mapset but I would like to copy it to another mapset for another purpose. Is this possible within GRASS or can I just copy some files over in the ...
5
votes
3answers
325 views

Is it possible, in QGIS, to create buffers with a set radius, but with individual values taken from the attribute table?

I am looking to create an output that consists of an 11KM buffer around a number of discrete points, where the buffer has a value defined by a column in the data sets attribute table. Is this ...
5
votes
2answers
535 views

Creating a multispectral image from scratch

I want to make a multispectral image from cero to do some tests on it. Something really simple like 5 completely uniform bands with salt and pepper noise on them or a square of different values at the ...

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