Raster Maps Geotiff tiles

Any extension for using Raster Maps (Geotiff tiles)?

If not, is any stalwart trying to make it ??

I want to try that, but I don't understand, what is the usefulness of the extension

It gives you the facility of using custom maps for offline use. At times certain organisations have their own maps (paper maps) which are scanned as tiff images and then georeferenced for use on GIS platforms (Desktop as well as mobile). They are very useful in far flung ares which are devoid of GPRS connectivity, where online maps do not work.

There is a open source app code on github, but NOT exactly as per requirement.

I am also interested in this. I found this thread from several years ago referencing using a flat map as a canvas, but I haven't been able to figure out how to implement it yet.


Welcome Tom. @Tom_Jarvela The link is a example showing how one can make a Flat Map using Blocks and an image of a map and a Canvas and use a LocationSensor to post coordinates on that 'map'. The discussion might might be the explanation you are seeking. It shows how to use a flat map as a canvas to draw on or post geocoordinates.


The example does not show how to make a raster map. It is a discussion showing a way to use an image (map) inside a Canvas. The developer can post geocoordinates onto that 'map' provided he/she knows the latitude, longitude of alternate corners represented on the map.

You can use it for very large areas

. This example shows a location posted near Dallas, Texas on a Mercator like NASA image of the World and the LocationSensor. When you use a Canvas for large area maps, plotting precision is dramatically reduced.


Couple of issues as far as doing it on MIT APP inventor

  1. U cannot do it for very large areas(If you are looking at precision). Maybe 1 degree Lat x 1 degree Long is doable. Better to start with a 15 min x 15 min map on a 300px x 300 px canvas
  2. You cannot use Geotiff Raster, but u could use a raster map as an image on a canvas
  3. It involves calculating pixels to degrees of Lat / Long
  4. It is a Degree to pixel coversion.
  5. You need to caliberate the map by knowing the map boundings ( Upper and Lower Lat, Left and Right Long) of the map.
  6. You need to start with the map of YOUR area and you need to know the GPS coords of your location.
  7. Calculate the centre (Origin) of the Map in Lat / Long values
  8. Put a point on your GPS coord (on the map)
  9. thereafter, calculate the distance in pixels, that the dot has to move on the canvas, with every D:M:S change

I am working on it. will have a test aia ready in a couple of days Will revert on this.

If you use a 15 min x 15 min map on a 300px x 300 px canvas, for every change of 1 min in geo coords, your dot has to move 20 px.Now the calculation has to be in X and Y axis. So u need to go down to Seconds instead of calculating in Minutes

1 Minute movement means 20 Pixels
60 Seconds = 20 pixels
3 seconds = 1 pixel

Location sensor default values are in Degree Decimal. U will need to convert to Degree Minute Seconds, then capture the change in seconds
A +ve change in Lat will move the dot UP
A -ve change in Lat will move the dot DOWN
A +ve change in Long will move the dot RIGHT
A -ve change in long will move the dot LEFT
(This is for locations in the 2nd Quadrant)
Like wise you need to know which quadrant you are located in to define the move Up / Down or Left / Right)

Use a software called gmd (Google Map Downloader) to download spatial raster data in various available formats. it is avilable for download on www.allallsoft.com)

Did you ever get a sample app going and have an example aia?