The fact that you can pin point the location of everything is the most vital part of geospatial technologies. Though the satellite images that we download from internet (say earthexplorer or bhuvan) have a predefined coordinate system, there many other things things that are not georeferenced. We can quote examples like scanned toposheets, guide maps, Images obtained from Google Earth etc. Here is a comprehensive set of videos to carry out the georeferencing process with different cases.
Georeferencing a Satellite Image Using another Georeferenced Image:
Say you want to georeference an image, and you have another image that is already georeferenced (say a satellite image downloaded from earthexplorer) and that covers the first image either wholly or part.
Now you will be taking the reference from the second image (that is already georeferenced) and georeference the first image.
Carry out this process in ERDAS
Same Process in ArcMap
Georeference Satellite Image Using Available Latitude and Longitude (GCPs):
It is quite possible that there is no reference image available or the resolution of the two images are so different that you find it difficult to precisely identify common points. In such a case if you have GCPs (latitudes and Longitudes of any point on the image), may be collected from Google Earth or using a GPS or any other means, you can correlate those GCPs with the points on the image and georeferenced the image.
It is quite possible that there is no reference image available or the resolution of the two images are so different that you find it difficult to precisely identify common points. In such a case if you have GCPs (latitudes and Longitudes of any point on the image), may be collected from Google Earth or using a GPS or any other means, you can correlate those GCPs with the points on the image and georeferenced the image.
Carrying out this process in ERDAS Imagine
Same Process in ArcMap (This process is also a method of downloading and Georeferencing images from Google Earth)
Georeference an Image from Google earth:
For a free high resolution image, Google Earth is a very good solution. However whenever the image downloaded from Google Earth will not have spatial references. So it is virtually unusable for any geospatial project. Following is a method to download and georeference the image from Google Earth. Here both image and reference is taken directly from Google Earth.
Carrying out the process in ArcMap
Another Method
You can try the similar process in ERDAS Imagine by following the similar idea and using the technique shown in the previous section (georeference using Latitude and Longitude in ERDAS Imagine)
Georeferencing A vector File:
There are cases where we end up digitizing an image and then realise that the image is not georeferenced. In such a case we will be needed to georeferenced the vector file, which is not as straight forward as a Raster file. Here we will be needed using spatial adjustment tool to carry out the process. Here we will be using another georeferenced file as reference.
Carrying out georeferencing of Vector File in ArcMap.
There are cases where we end up digitizing an image and then realise that the image is not georeferenced. In such a case we will be needed to georeferenced the vector file, which is not as straight forward as a Raster file. Here we will be needed using spatial adjustment tool to carry out the process. Here we will be using another georeferenced file as reference.
Carrying out georeferencing of Vector File in ArcMap.
Changing the Projection of A georeferenced file:
There are many projection system, each suitable for various areas and various projects. Dpending on the requirement, there might be need to change the projection from one to another. Here is the tutorial in ArcMap to change the projection of a georeferenced file.
There are many projection system, each suitable for various areas and various projects. Dpending on the requirement, there might be need to change the projection from one to another. Here is the tutorial in ArcMap to change the projection of a georeferenced file.
