Question

Hello I am developing an application where .jpg images are to be used as maps. I am developing this application for trekking spots near my university where internet connection is too low.

So using only the pre-saved image as the map and GPS, I wish to make the user navigate. I want an idea of how to display the image which can be panned and zoomed. Also i wish to add an overlay over the image to display his current position. .

Plz give a brief idea….

Answer 1

Welcome to Stack Overflow — this is certainly possible with Google Maps. You can tell the map to load images for you — providing the bounding corners for each image.

This is not an easy problem to solve as there are many, many moving parts:

1. The easy part is actually getting images with geo-referenced corner points — the easiest format for this is probably GeoTIFFs (or just an XML listing the corner points)
2. You have to manage the image caching, load too many images at once and you’ll blow out all the available memory
3. You have to monitor the map for every pan/zoom/etc to load/unload images as appropriate. Ideally you’d load low res images when you’re zoomed out and progressively drop into higher and higher resolution images

How is this acheived? Well – that’s the hard part. You basically need to extend Google Map’s Overlay Class and override the draw method.

1. You give the corner points for the image (and the image bitmap itself) to the map as part of the draw method
2. When the image is in view, load it, when it’s not in view, unload it.
3. When you load/unload images call postInvalidate on your map view to force it to redraw the tiles.

It is worth noting that Google Maps will cache some imagery — if your university’s campus is small enough you may be able to fit the whole thing in the cache. Then you don’t have to do any fancy work at all.