Add zoom controls

[bollian]

There are a lot of controls normally associated with image zooming, and we should probably implement all of them:

• reset zoom level
• zoom in/out buttons (steps zoom level by ~10% or so)
• scroll to zoom

Some apps use ctrl+scroll for zooming, and then keep the normal scrolling behavior of moving the image up and down, left and right. For us, the most common use-case is zooming in and out, and we want click-and-drag controls for panning.

These scheme has the side benefit of maybe being easier to port to a tablet.

[manavgandhi17]

Just wanted to tag in on this zooming stuff. Would it be possible to have the center of the zoomed location (in pixel by pixel)? I am assuming that we will always be zooming in on a target - so the center of the zoomed location will be the target center. If we have this location (in pixels), we can easily use some vector projection math to figure out the lat, long of the target. Since we will know the lat, long of the image's center and compass heading (from metadata) and it will have a known PPSI (from testing).

Also, the info for lat, long and compass heading is in "exif metadata" form. We don't have any images that include that rn - but just wanted to let you know.

[manavgandhi17]

I might try to get you all an example image with lat, lon and compass heading in the metadata by mid-Feb. Won't have a target in it - just some metadata attached for testing functions.

[bollian]

The current plan is to have the latitude and longitude calculated at the center of wherever the image is zoomed in to.

Currently, we've got some preliminary zooming implementation working, though it only zooms towards the center of the image instead of where the mouse is. It could also use some simple buttons for stepping up/down the zoom level.