Hello, I am using ArcGIS 10 and have several orthoimages (Landsat 4-5 TM) that I got from the GLOVIS site that I need to mosaic together and orthorectify. I don't have any experience with this, so some questions may be relatively basic. Some info about the images that may be helpful:
Number of bands - 3 Cellsize (X,Y) - 1,1 Format - JFIF Pixel type - Unsigned integer Pixel depth - 8 bit Pyramids - Absent Statistics have not been calculated
From what I understand, I need images that have RPC (Rational Polynomial Coefficient) values, and a DEM in order to orthorectify them. The images, however, have no RPC values associated with them, although I do have a DEM I can use. The images also don't have any spatial reference, so I can't mosaic them together. Furthermore, I have no idea what the original geographic coordinate system was, so I can't use Define Projection to rectify that problem.
Basically I need to know if it is possible to orthorectify images that don't have RPC values, or if I can calculate them, and how I can figure out a spatial reference for the images as well.
I should add that the spatial reference for the image is an invalid extent, which means that I will most likely have to georeference the images, correct? If so, the images are at 30m resolution and don't provide much detail close up. Assuming that I could find a layer that I could georeference the images to, I don't see how I could accurately do the job because of the lack of clarity close up. Yikes, help!
At a 30 m resolution you should still be able to distinguish major features like road intersections and other boundaries. Do you have a vector dataset for the same area that you could georeference the images to? If not, you might open one of the basemaps in ArcMap or get a layer from ArcGIS.com. You can't orthorectify, but you can georeference. There is a georeferencing video that should be helpful: http://video.arcgis.com/watch/376/georeferencing-rasters-in-arcgis
However, the fact that you're calling them orthoimages, implies to me that they've been orthorectified, so maybe they've just lost their spatial referencing. In this case you only need to collect a few tie points.
Hi, thanks for your reply. I don't think that the images have been orthorectified previously because they are just raw satellite images. Perhaps I should have called them simply satellite images, but I am kind of new to this world. I am in the process of georeferencing, thanks for your suggestions about the pyramid building and the statistics. So, assuming I can georeference the images, is there a way I can calculate the RPC values in order to rectify the images, or to rectify without RPC values??
Hi, I am still having trouble seeing anything in any detail up close, even after building the pyramids (level 4, bilinear) and calculating statistics. There is no way I can make out any roads or definable features to georeference to. I tried resampling to a smaller pixel size, but it didn't help. Also, I can't find any information on calculating RPC values, so I am really confused as to how one can orthorectify satellite images if RPC values are necesary, yet you are unable to calculate them. Thanks again for any help!