Tagged Questions
0
votes
0answers
16 views
Loading raster from PostGIS DB into QGIS: succeeded yesterday, fails now
I have a PostgreSQL(v.9.2)/Postgis(v.2.0.3) database which includes raster layers (added through raster2pgsql).
To open them in QGIS (v.1.8.0-Lisboa), the "Add Postgis layer" menu will not work; ...
1
vote
1answer
23 views
Why does the Zonal Statistics tool always return 0?
I have a slope raster created from a DEM raster with the DEM Analysis tool.
Now, I would like to calculate the average slope in a given area represented by a vector polygon layer.
I thought I could ...
1
vote
0answers
21 views
QGis Grid statistics for polygons error - Module caused access violation!
I'm trying to calculate statistics for a raster layer using an overlaying polygon layer, I'm using SAGA "Grid Statistics for polygons" function, but it returns an error, sadly.. So in the sextante log ...
4
votes
1answer
54 views
Raster to vector with gaps in Landsat ETM
I need to find size of water area from a raster (jpg) using QGIS 1.8.0-Lisboa. The raster is a Landsat image with gaps of data in it.
I used Polygonize, but the output file shows wrong polygon size ...
3
votes
1answer
39 views
Is it possible to batch clip rasters in Quantum GIS?
I have been able to batch clip rasters in one directory using python in ArcGIS. However, I am not sure how to do the same in Quantum using the python console. Is this possible? If there are different ...
1
vote
0answers
53 views
How to get Lon/Lat values from the postgis raster type column
I have a tiff raster in my PostGIS 2.0 database. I want to get the value lat/lon and extra data like temperature from the raster type column in postgis table.
I want the table with columns ...
1
vote
0answers
56 views
QGIS: Different projection result for on the fly and transformation
I am a bit confused about the result of a re-projection/transformation of a raster in QGIS 1.8 (Lisboa).
WGS84 to WGS84/UTM34N. When I use the 'on the fly' transformation the resulting raster has a ...
0
votes
0answers
30 views
Problem with Georeferencer not scaling TIFcorrectly
I am trying to use QGIS and the Georeferencer to digitize paper maps but I am unable to get the raster to rotate afte I pick my control points. Below is a brief outline of the steps I used to ...
0
votes
0answers
24 views
QGIS: Unable to project raster layers correctly on a Toshiba Tecra 64# Win7
I know how to project a raster, I can do it on other machines. On this particular machine the raster loads but are no where near the correct position as if the datum is on another planet.
5
votes
1answer
61 views
Georeferencing a jpeg in QGIS but the scale is way off
I've gone through the really helpful walk-through(s) of how to georeference a jpeg in order to make it a layer, but after inputting the coordinates (either by typing in actual coordinates or clicking ...
3
votes
1answer
109 views
How to import QGIS Raster into PostGIS
I have created a IDW heatmap using QGIS 1.8.0 and need to import the raster into PostGIS 2.0.1. QGIS saves the raster layer as a .asc file.
How do you import the raster into PostGIS as a Raster? What ...
2
votes
1answer
90 views
How to reclassify a float raster?
I have three rasters which represent distance (in metres) from certain things (bus stops, parks, libraries). I would like to reclassify these rasters so that they get integer values based on the ...
2
votes
0answers
62 views
Raster area (QGIS) problem explained
I would like to know the area that each value in a raster has... The raster I have has values from 2-15 and I would like to know the area that each value is occupaying within my polygon... Thanks!
I ...
0
votes
0answers
36 views
Why are areas of raster and polygon after digitization not matching? [duplicate]
I have followed the answer given in this question:How to calculate the area of rasters in QGIS?
I vectorized and calculated the area using geometry columns but I a faced a strange problem.
When I ...
0
votes
0answers
12 views
How to create symbology? [duplicate]
Please suggest how to create symbology in QGIS? As I am Infrastructure layer with the help of QGIS and I want to represent different roads with different colors and widths but right now I am unable to ...
0
votes
1answer
105 views
Problem to clip a raster with a shapefile
I need to clip a rasterlayer with a vector layer. When I try this, the following error appears:
**ERROR 1: Attempt to create 0x0 dataset is illegal,sizes must be larger than zero.**
What am I ...
3
votes
1answer
49 views
Differences in raster extents in gdalinfo, SAGA & Quantum after resampling
I recently resampled a raster file using SAGA's Resampling module. The aim was to widen the extent of the new raster to two decimal places, where the original raster has three decimal places. The ...
1
vote
2answers
72 views
Reducing the resolution of a huge raster
I'm not much of a GIS user, but I've got a big ascii file that I'm trying to convert into a
lat long data
x1 y1 d1
x1 y2 d2
x1 y3 d3
x2 y1 d4
...
etc
format, so that I ...
0
votes
0answers
38 views
Display raster outlines
I guess mine is a very simple task, however I don't know how to solve it.
I m trying to display the outlines of a raster created from a polygon shp.
What I would like to come up with is an image where ...
2
votes
1answer
27 views
Can TimeManager animate a large number of rasters in QGIS?
I understand that as of a year ago, the TimeManager plugin was not intended to handle more than a handfull of rasters. This post is in blind hope that this has changed!
I'm trying to create a map ...
1
vote
1answer
82 views
How to invert polygons (or other options for exterior styling)?
I have a shapefile containing many polygons that I want to use to mask a raster. I have tried gdalwarp -cutline <shapefile> -crop_to_cutline -srcnodata -9999 -dstnodata -9999 ...
4
votes
4answers
110 views
How to display a “Save As” dialog for raster files?
I'm writing a QGIS plugin in python. I need to show a "Save as" dialog window in order to allow the user to select the path of the output raster file. Do I need to create a QFileDialog and manually ...
1
vote
2answers
79 views
How can i make a polygon of cells of a raster
I have 100 rasters, each raster has the same cell size and extent and i want to make a polygon over of each cell. Can anyone help me doing this?
Thanks in advance.
2
votes
0answers
35 views
Is there a tool for automated quality assurance for vector data captured on raster data?
I wonder whether is any tool(or script) in ArcGIS or QGIS which allows to make an automated quality assurance for vector data captured on raster data?
vector data on binary raster:
1
vote
0answers
32 views
How can I create a multi layer exportable file (.xcf .psd) from multiple raster image in QGIS?
I have many raster file of the same zone but in differents spectral bands. I would like to create an exportable file of a small portion that can handle different layers. So in practice I would like to ...
3
votes
1answer
100 views
Save Visible WMS layer to file
Is there tool to save currently visible WMS layer to file in QGIS, or some place in QGIS where you can get needed xml to fetch it using gdal ?
2
votes
1answer
103 views
How to reclassify grey scale tiff in qgis
I downloaded a raster image of the sea floor age. The values in band 1 ranges from -32768 to 32767. I need to reclassify it to no. of million of years to make sense of the data. How can I do so? I try ...
0
votes
0answers
23 views
How to add attribute table to a Raster file in Quantum GIS [duplicate]
I have a raster file, in Quantum GIS, without attribute table but I need to add one attribute table with the information of the pixel values. I can compute the statistics with the histogram but i need ...
2
votes
1answer
48 views
How do I stop null values from being assigned extreme color values?
I have a raster surface that I kriged in Surfer and imported to Grass GIS but when I view it in QGIS, the null values outside of the interpolated surface take an extreme value and wash out the ...
2
votes
1answer
73 views
What is No Data Value?
I'm looking at the transparency window of the layer properties of my "Heat map". How does the No Data Value effect a raster layer. I'm assuming an initial setting of -9999 sets it out of the way, so ...
5
votes
1answer
163 views
Best Way to Handle Many Raster Files in QGIS?
I have a project with a large number of raster files, but it is becoming very slow. I wonder which is the best way to handle all this. I'm simply georeferencing these files creating .wld file (geoTiff ...
2
votes
2answers
140 views
How to calculate the area of rasters in QGIS?
I have been working with some rasters and would like to know how to calculate the area occupied by one element of a raster in Qgis.
1
vote
1answer
158 views
What are Bands, Dimensions, and Histograms in QGIS?
First; I can see a band as synonymous with a channel in an image editing program like GIMP, is this correct?
If so then bands play the role of color mixing and masking. Are there any other ...
2
votes
1answer
36 views
What defines a Class in the Heat map plugin?
What defines a Class in the Heat map plugin? As in:
"Black holes like that are usually caused by raster values exceeding the range of the color ramp. Try adding another class with a higher associated ...
3
votes
1answer
201 views
How to convert jpg file to shapefile?
I am developing a GIS application like this:
By now my steps are:
I have got a jpg file, 5040 x 8179 dimension. In this map, the roads, rivers, towns etc. are marked.
I am using .Net to develop ...
3
votes
0answers
80 views
How does Zonal statistics handle pixels that are on the border of the polygon?
I am using the plugin zonal statistics to calculate the sum of the raster cells within polygons. How does this plugin handle pixels that are on the border of the polygon, are those cell values ...
1
vote
1answer
49 views
Problem loading raster to PostGIS using QGIS
I am having trouble loading a raster (.asc) file to PostGIS 2.0.1 using the plugin Database - PostGIS Raster - Load raster to postgis in QGIS 1.8.0 on Win Vista 64 bit. I get the following error ...
1
vote
1answer
100 views
Qgis - Raster clip Problem
I tried to use the Raster (Extration) tool "clipper" and I always get this error log:
What is my problem?
Fehler bei der Ausführung von Python-Code:
Traceback (most recent call last):
File ...
3
votes
1answer
102 views
Reclassification of environmental values
I've started to use Qgis recently.
I have a logical question.
I'm trying to reclassify a raster. The values in the raster are depths, obtained by an interpolation.
The original depth values (of the ...
0
votes
1answer
105 views
How do you use 'reclass' in GRASS?
It could be user error, but for some reason, the reclass tool is just hanging and hanging...
QGIS 1.8
Compiled against GDAL/OGR 1.9.2
Ubuntu 12.04.1
Running the tool from the Sextante toolbox
Input ...
0
votes
1answer
52 views
Sextante (SAGA) “Normalisation” problem
I don't understand the SAGA-module "NORMALISATION". In SAGA Gis I just can define one MIN and one MAX value. In QGis I have to define 2 of both. How to handle that exactly?
3
votes
4answers
93 views
Combining UK OS Historic Digimap Tiles
I'm assisting a retired user in combining a large number of raster tiles downloaded from Historic Digimap http://edina.ac.uk/digimap/description/historic_overview.shtml into one project in qgis.
I'd ...
4
votes
2answers
98 views
How to create a colormap where colors diverge at value 0 in QGIS?
I calculated a raster as difference of two other rasters. Now I want to create a colormap where one colour represents negative values and one colour positive ones. The two colours should become ...
0
votes
2answers
143 views
Digitizing from OpenLayers Plugin in QGIS, or create raster?
Is there an easy method for digitizing from a layer added from the OpenLayers pluggin. As i cannot snap to it or use it as raster so the entire map does not load?
two separate issues there.
1
vote
0answers
52 views
How I can incorporate results of histogram stretching into georeferenced image?
I have one channel 8 bit raster and when I open it in QGIS with histogram stretching "on the fly" it looks fine. How I can recalculate original raster accordingly changed histogram?
3
votes
3answers
196 views
How to extract raster values and create 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?
1
vote
2answers
83 views
Put color for raster data(aspect.tif) on QGIS1.8.0
I create aspect.tif from DEM file.
I could put the values(0 to 360)from contrast enhancement.
I could set color from color map(freakout or Pseudocolor).
In here, the data is shown by only 4 colors.
I ...
4
votes
1answer
134 views
How can I avoid reprojection gaps when merging DEM rasters?
I have two raster DEMs in same resolution I want to bring together. I was using the merge-function in SAGA, GRASS and QGIS but I always get the following result:
What do I need? Where could the ...
1
vote
2answers
291 views
QGIS Raster Calculater Syntax
I am trying to use the raster calculator in QGIS to combine a number of rasters. I want to calculate a mean, this is easy:
(raster_1@1 + raster_2@1 + raster_3@1) / 3
I then want to create a max. ...
0
votes
0answers
132 views
Output of QGIS raster clipper not as expected?
My goal is to clip a raster with a polygon in QGIS 1.8. Based on an article I read, this should be a pretty straightforward task. However, the output appears to be empty. The raster produced is the ...
