I have currently been Geo-referencing historic imagery for the past 3 months and would like to share my thoughts on some issues regarding project results and time.

As you may know, I am tasked with Geo-referencing historic imagery from the years 95′, 75′, and 59′ to the most recent imagery available to me, 2015. There are 140 images per year and about 105 of them that actually overlay the 2015 imagery. I have never done another Geo-referencing project of this size, so I am not sure if 105 images is a lot, but it seems like a lot. In addition, the images have to meet a certain accuracy standard, which is reasonable and understandable, while also tethering to each other on the edges. Essentially, images and imagery have to perfectly overlap and mosaic. These are all reasonable expectations from someone tasked with Geo-referencing.

However, time must be taken into consideration, especially during a task as tedious and vast as Geo-referencing. To give a little background, I began the tasks by originally putting in a conservative amount of control points (6-12) and lining up the images, however the edges would usually not line up due to camera positioning, sun angle, etc and this resulted in a revision, which is good for myself as I acquired more practice. During my revision, I focused on tethering the images together with a similar amount of control points (6-12), not so much lining them up to the imagery, although they did line up, just not as accurately or precisely as my first run through. This attempt also resulted in a revision, accompanied by a request to tether and accurately match the images to the imagery. This is where my post comes in.

In order to acquire both accurate and tethered imagery, I needed to place many more control points. Common sense would tell you that placing more data would require more time. Control points changed from 6-12 to 14-22, and placement and transformations became more prioritized. Image placement time skyrocketed from 5-10 minutes to 30 minutes – 1 hour. This quickly resulted in a scenario of something that could have been completed in a reasonable amount of time to something that may take months depending on your devotion to such a task.

The question for management becomes: Are we willing to spend such and such on a near perfect product or should we sacrifice some accuracy and quality for time and money. This question depends on what the Geo-referencing projects final use will be. In regards to my project, I am not sure the exact intent, but I think its eventual purpose will be public viewing. If that is the end goal, I think it would be best to skimp on some accuracy as the public does not generally have a professional eye and will not notice the small details such as perfect tethering and/or complete imagery line up.