Quantum gis create world file

The software GUI contains many of the same geoprocessing and cartographic tools as well-known ArcGIS, along with an extensive Python library that can be used to automate processing. When data is collected via a remote sensing platform, whether that be a camera in a plane, or a thermal sensor in a satellite, the data collected must be aligned to real-world locations in order to be useful.

Geo-referencing in GIS allows the user to do just this, using a known coordinate system and known points on the ground to align remotely sensed data so that it may be viewed, queried or analyzed with other geospatial data. These reference points are known as ground control points, or GCPs, and are stored in the metadata of. Creating GCP's allows GIS software to transform the data into different geographic referencing systems by shifting, scaling, rotating or skewing the imagery. Before beginning to aquire the data necessary for this exercise, it is best to create a folder to organize all of your project elements into.

Somewhere on your computer that is easy to access preferably in your C: drive on windows, or HOME directory on Linux , create a folder named Georeferencing Exercise'. This will be the location where we store all our data, as well as the QGIS project files.

The air photo used for this example can be located here: [1]. At this link, scroll about a third of the way down to the section labelled Available Themes.

Select the bottom-most link s - air photos from uOttawa. Refer to the Figure 2 to visualize the location of the desired photo. Click the dot, then the link that appears. Once on a screen with the photo as per figure, right click the photo and select Save Image As Save it to the folder made earlier.

In terms of reference vector data, study the image selected and locate as much reference vectore data as possible. ZIP , and the river [4]. Download these three vector datasets, and extract them into your project folder made earlier.

Since this particular photo was taken in , there will be sections of the data that do not exist in the image, but do not let this discourage you, as the sections that do will still be accurate, though created over 80 years later.

If you have Windows, check your specifications, as either you will use 32 bit or 64 bit. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. How to generate world files for raster X? Ask Question. Asked 10 years, 4 months ago. Active 2 years, 7 months ago. Viewed 13k times. Improve this question.

Geotiff is what I have had the most luck with in different software. It only looks at. Add a comment. Active Oldest Votes. Improve this answer. R Thiede R Thiede 4 4 silver badges 12 12 bronze badges. It doesn't do is follow the convention of naming the extension after the input, e. Accepting this as the correct answer even though I didn't use it, as it the most complete solution. Just one detail: when I rotate the image, the program creates a image bigger than the original, to let the rotated image fit in.

My question is now similar to this one: georeferencing aerial photos with only known centroid. There are many conventions for image world files. What they share is the image-to-world transformation matrix. Where they differ is in how the matrix elements are represented and in how the pixels are referenced: more about that at the end. In almost all cases the world file represents an affine matrix not the full projective matrix. The affine matrix has six coefficients, often written in 3 x 3 matrix form as.

Fortunately, you don't need to do much arithmetic to decipher this, nor do you need to learn any more math than you already know, because there is a nice simple interpretation of what this matrix means.

It says that:. The point at 0,0 in the intrinsic image coordinates usually column and row corresponds to the point C,F in the world. These coodinates come from the third rightmost column of the matrix. This is the sum of columns 3 and 1. This is the sum of columns 3 and 2. To create a world file, then, you have to work out the values of A But the solution is easy :.

A,D are obtained by subtracting C,F from the coordinates of where you would like 1,0 to be. This is often the second pixel along the first row. B,E are obtained by subtracting C,F from the coordinates of where you would like 0,1 to be.

This is often the second pixel along the first column. For example, if you would like to rotate the image 90 degrees counterclockwise around its origin, place the origin at the point , , and scale each pixel up by 30, you can easily work out by drawing a picture, for instance that. Reason: rotating 1,0 sends it to 0,1 ; scaling up by 30 gives 0,30 ; translating by , gives , Reason: rotating 0,1 sends it to -1,0 , etc.

You can still get it wrong, depending on how your software intrinsically references the pixels in the image. The principal variations are i rows can go from top to bottom instead of bottom to top, placing the image origin in the upper left corner and ii the image could be referenced by row, column instead of column, row.

The first one causes the image to be reflected across a horizontal line while the second one reflects it across a diagonal line. If you get either of those two errors, you will immediately see what's going on and will know what to fix. Documentation can be so obtuse or non-existent that in practice I just try it, deduce the convention from how the image turns out, and proceed accordingly.

Note that rotations by non-multiples of 90 degrees and differential rescaling require resampling and therefore are not universally supported.

First of all, world files Wikipedia article do not contain map projection information , so you have to know the projection of your image and then tell QGIS which one to use. Perhaps you should try using GeoTIFFs instead, they are much more precise in terms of georeferencing. Affine transformations are given by 2x n matrices and if we have n points x1 y We must also take into account the parameters of a worldfile for the position of the 0,0 point of the raster: lower left for affine transformation, upper left for gdal and middle of the upper left pixel for worldfile.

Qgis support without problem rotational factors in the worlfile parameters B and D different of 0. It use GDAL.