topic Re: Problem georeferencing old aerial images in Data Management Questions

Problem georeferencing old aerial images

JacobCoble — Thu, 31 Oct 2013 12:26:38 GMT

They are just scans. Their resolution is between 2 and 3 ft. They seem to have been taken at 12,000 ft. They are black & white - 400 aerial images. We got them as Mr. Sid files. There are a lot of weird problems. I converted them to jpegs. Each tile (image) is 234 inches across! I resampled them down to a smaller size so each jpeg is 30 mb in size. I think this is still too big for what the images are. Even though the images are black and white, each image has 3 bands. I don't think I have ever seen a black and white image made of 3 bands - very odd. Each band is a little different so I think I need to merge the bands of each image. A co-worker georeferenced an image, saved it as a grid and the grid it became a large file impossible to work with. The georeferenced image would not export as a jpeg.

The bottom line. I want to have each tile as a georeferenced jpeg file (I think). Not everyone here is ready to use a mosaic dataset - so I will have to make the images available as a raster catalog and also mosaic them into a single Mr. Sid file. Now, I would like to use a mosaic dataset to help process the images. Even though I cannot use a mosaic dataset right now to publish the images (long story) I do want to use a mosaic dataset as a workspace and production tool. But the problem is, how do I convert the images to something I can work with? I can't resample the images to a reasonable file size and still have okay quality. I am sure I need to make each image so it is one band, not three (that should help with file size but I am wondering what else I should do). As I mentioned, we tried georeferencing an image and it could not be saved as a jpeg. We saved it as a grid but that became a very large file for some reason. I think each image should be under 10 mb and easy to manipulate. Besides turning the images from 3 band to 1 band, just what should I do to make the files a reasonable size before we georeference them? What things should I do that I might be overlooking?

Re: Problem georeferencing old aerial images

NeilAyres — Fri, 01 Nov 2013 06:13:05 GMT

Whenever I need to "reformat" image files from, say, 3 band RGB (24bit) to single band grey scale or pseudocolour (8bit) I tend to use Adobe Photoshop Essentials. Its good at that sort of stuff. Not sure that PS will read in sid files though.
Cheers,
Neil

Re: Problem georeferencing old aerial images

PaulVanDyke — Sat, 02 Nov 2013 21:43:01 GMT

Jacob,

I've been working with a similar system. I've been downloading 1950's imagery of my area of interest from http://earthexplorer.usgs.gov and they are scanned images of original aerial frames. I've been processing them with agisoft photoscan to make them a seamless orthophoto by cropping out the frame edges and registration marks. Once they are properly aligned in photoscan I add markers as ground control points. I'm using GCPs in the older imagery that match my current imagery. Once properly orthorectified in photoscan, I export the imagery with a world file. I can drop that into ArcGIS and it matches quite well.

I expect that some of the issue may be that your imagery is true airphotography, and it has not been orthorectified yet. Do you have some sample images that I could take a look at?

Good luck,

Paul