@Klepperton Yes I did offer up a similar service for auction at the HPP silent auction, but included all the digitization into orienteering map symbols traced from the ortho photos, but with no fieldwork.
As to whether there is a science in importing online aerial photos, in my experience you either get nice data sources (geotiffs, or other image files with georeferencing.) or bad data sources (without georeferencing). Nice data sources, such as from
http://opendata.kelowna.ca/, give you already georeferenced data, allowing you to match multiple basemaps up perfectly and easily. (By the way this does appear to be an option in Toronto, you just have to pay for it:
https://www1.toronto.ca/wps/portal/contentonly?vgn...) Open Street Map
Then there are not so nice data sources which you have to georeference. This is your screenshot from google maps, bing maps, etc. which has the advantage of being available everywhere around the globe. Sometimes you can even get contour data as image files for free (which you then spend hours tracing...) from some city websites. When this is the case, I do basically what gordhun does, except I just use OOM and never saw enough advantage in using OCAD to pay for it. So I just trace everything from the photo once it is lined up with Open Street Map. (sidenote, open street map data is pretty sparse where I come from, so it wouldn't really be worth it anyways...
http://www.openstreetmap.org/search?query=salmon%2...). Then, as you say, "there's no real science when importing online aerial photos".
And then there is what Toronto has (which I have never seen anywhere out west). You don't have to pay for it, it is georeferenced, it just takes a lot of work to play with it. So I got my older brother to figure it out for you! Everything from here on out is all him:
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GDAL and QGIS
You need to install both GDAL (
http://www.gdal.org/) and QGIS (
http://qgis.org/en/site/)
Follow
http://www.qgistutorials.com/en/docs/working_with_..., using the Toronto server (
http://gis.toronto.ca/arcgis/services/primary/cot_...?) as the URL. After adding the layer, zoom to the area you want. Click Project->Save as image, and save it wherever you want to.
Next, open a command line in the folder (in older versions of windows: shift+right-click, Open Command Prompt IIRC, in newer versions Windows+R, then type cmd and hit return. In command prompt, type cd and then the folder name) that you saved the PNG in. Run the following command:
gdal_translate input.png -a_srs EPSG:32617 -of PNG -co WORLDFILE=yes output.png
Replace input.png with whatever you called the file you saved above. This will create a file called "output.png" with a georeferenced world file that uses UTM 17N (which is what Toronto is).
GDAL Only
Download the file from (
here). This is a prebuilt file for Toronto's open data. Open a command line in the folder you downloaded it to. Edit the file (any text editor, eg notepad, will work). Replace the UpperLeftX, UpperLeftY, LowerRightX, LowerRightY with the corners of your map with the coordinates you pick from
http://epsg.io/map#srs=2019&x=312399.075406&am...Now, run the command
gdal_translate toronto.xml -of PNG -outsize 2000 2000 -co WORLDFILE=yes input.png
where each of the 2000's is the pixel height and width of the output image (you can change this, bigger is better quality but slower to render in OCAD/OOM). Now, convert the projection as in the QGIS/GDAL option above with the command
gdal_translate input.png -a_srs EPSG:32617 -of PNG -co WORLDFILE=yes output.png
The advantage to using QGIS is that you get to preview what the image will look like before you save it, plus its slightly more point and click, however, you do need to install another program.
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Note that it might be possible to skip some of these steps using OCAD, but we are limited to OCAD 9 (which I almost never use except for updating a few maps without wanting to change file types to OOM) so can't help there.
PS: Alternatively, if you are not dedicated to using OCAD and could endure using OOM, send me an email through my profile and we can work out my brother and I setting up your maps.