Alpha Blending Perspective and Photograph
Guth and Craven, 2006 describe a
technique to register oblique photos take with a consumer digital
camera or webcam.
||Digital photo taken from Black Butte Fire Tower,
Oregon. It shifts to a DEM perspective view with TIGER
Create Perspective view
- The same pixel height and width as the photo.
- From the same position as the photo was taken, at the
same elevation above the ground.
- The same angular field of view as the photo.
- The same azimuth as the photo.
- The same pitch as the photo.
- If the photo has roll, you can rotate it back to
horizontal. The Tools
submenu from the File
menu has a "Load image" option which has a
"Rotate" menu option that can be used.
- If the photo is too large to fit on your screen, you can
reduce its size so that it is manageable. Paint can
do this. This will lower you attainable accuracy, and the
program should now work with slider bars so you can use
the full resolution photo. This is a case where a larger
monitor will greatly simplify operations.
On the file menu of the Perspective
view view, select the "Alpha
blend bitmap" option.
- The slider that will appear on the panel at the bottom of
the perspective view lets you adjust the opacity of the
- A button on the new panel lets you save a single blended
- A second button lets you save a movie, showing the
perspective and photograph blending into one another.
This is a complicated operation. It pays to pay strict
attention when capturing the photo to keep the camera
horizontal. You may well have to iterate multiple times to
get a good match.
|Fig. 1 of Guth and Craven,
2006. This is an iterative process, but our
experience suggest that after an initial rough cut to get
all parameters correct, this provides an efficient way
Panorama view might
help with matching photograph.
Last revision 6/4/2015