Discussion: Aerial Imagery Resource Now Available to Orienteering USA Clubs & Mappers

Through an arrangement with Pictometry Online, Orienteering USA clubs may now access one of the largest sets of high resolution ortho- and oblique imagery taken during leaf-off periods from across much of the US. Images can be downloaded at a nominal cost to aid in creating new maps or for updating existing ones.

For more information, head to the overview with a FAQ that now posted in the Mappers/Resources/Aerial Imagery section of the Orienteering USA website, at URL http://orienteeringusa.org/mappers/resources/aeria....

Our goal is to make the creation and updating of high quality orienteering maps better, cheaper and faster, and we hope that this resource will help meet at least some of those goals for your club.

-Greg Lennon
Orienteering USA Mapping Coordinator

Out of curiosity, what kind of resolution are we talking about? The oblique photos on the website look pretty shiny, but demo photos always do. :)

There are two levels of resolution: "community" level at 12" per pixel and "neighborhood" at 4" to 6" per pixel.

And I'm just as wary of demo photos as the next orienteer, so I'm looking forward to learning on average how much less "shiny" the photos for areas needed and used by US mappers are compared to those demos. It's still too early to say, but at least for a handful of images I've obtained over terrains here in the Mid-Atlantic area that did have coverage, the photos have been both pretty good and quite useful.

Nice....that's certainly in the useful range. :)

BTW, your FAQ is a bit incorrect:

Google images...can't be exported in a georeferenced format.

It's actually relatively easy - certainly into JPEG + world file format, at least.

Over here we don't have to worry about leaf-off photos, our trees generally never drop 'em anyway. :)

Note that in the northeast, NY, PA, MA, NJ and DE all have statewide high-quality, high-res color orthophotos, georeferenced, available for free download from various state and county GIS agencies. Some states were one-time collections (all are within the past 3-4 years), and notably NY and PA have funded repeating cycles. Always good to check govt agencies for coverage first...you might get lucky. If not, try Pictometry for coverage.

Here are links to those northeastern states' online orthophotos. Lots of other GIS datasets from these servers too:

NY - 0.5 ft, 1ft, and 2 ft/pix, 4-5 year repeat cycle, leaf-off color orthos:

Program descrip and data download:
http://www.nysgis.state.ny.us/gateway/orthoprogram...

PA - 1ft/pix, 3 year repeat cycle, leaf-off color orthos:

Program descrip:
http://www.dcnr.state.pa.us/topogeo/pamap/data.asp...

Data download:
ftp://pamap.pasda.psu.edu/pamap_imagery/
(or via the imagery navigator here: http://www.pasda.psu.edu/)

MA - 15cm and 30cm/pix, 2008-2009 no defined repeat cycle, leaf-off color orthos:

Program descrip and data download:
http://www.mass.gov/mgis/colororthos2008.htm

NJ - 1ft/pix, 2002 and 2007-2008 no defined repeat cycle, leaf-off color orthophotos:

Program descrip and data download:
http://www.state.nj.us/dep/gis/

DE - 25cm/pix, 2007, no defined repeat cycle, leaf-off color orthophotos:

Program descrip and data download:
http://datamil.delaware.gov/geonetwork/srv/en/main...

Is photogrammetry required to produce a base map from these images?

These are only rectified aerial photos (orthorectified, meaning they can be used like maps). So no, they can't be used to make contours for a basemap. You'll have to get the contours via other means.

The "bird's eye view" versions at Pictometry are not rectified, so they have to be used differently.

To expand beyond just the northeast, for public domain US orthoimagery head to http://seamless.usgs.gov/, the USGS Seamless Data Warehouse server. The highest resolution (and generally leaf-off) imagery can be found in the "HRO" (= high resolution orthoimagery) section.

As for exporting georeferenced Google Earth images, is there really a way to do this directly? The only ways I know of are to either georeference your image using another program (ArcMap, Global Mapper, etc) or to create a text (World) file knowing the upper left coordinates of your image and then calculating by hand the scale factor (meters/pixel). Both of these are clearly just ways to work around not being able to directly export a georeferenced Google Earth image (i.e. automatically with a world file at least if it's a JPEG image, or to get a GeoTIFF image, etc).

Do you know of a way from within the (free version of) Google Earth to directly export a georeferenced image? If so, please explain how.

You can't within Google Earth itself. (that I know of)

There's a wonderful little program called Mobile Atlas Creator which can strip tiles out of lots and lots of different map sources, including Google Maps/Earth, and stitch them into one image. One of the output formats is OziExplorer (.PNG and .MAP) which can then be easily converted into .JPG and a world file (by grabbing the coordinates/pixel size etc out of the .MAP file and creating your own world file, which is a well-documented format.)

I find this site useful for converting lat/long coordinates into UTM (for the world file) without bending your head. :)

Be aware that Google will block your IP for a while if you try to download too much in one sitting. Don't ask me how I know this. *grin*

A "georeferenced Google Earth image" is a nonsense in some places, I guess depending on their many arrangements for acquiring imagery. I have had problems fitting images to other data especially in steep country, suggested that various sources of distortion have not been removed. And there are many places where you can see a displacement across photo boundaries. When I use GE downloads I fit them myself to a framework established by more trustworthy photos.