Reading latitude longitude points from a BMP/PNG file?

Aquarius_Girl · 07-10-2012, 02:52 AM

Suppose there is a map file saved as a BMP.

Is it possible somehow to read the latitude longitude points from that BMP file?

graemef · 07-10-2012, 03:06 AM

if you know where the data will be on the image then you can crop that part of the image and then pass it through an OCR library - such as tesseract.

If you don't it would be more problematic because you may have other pieces of data which once you have converted using ocr may look like valid lat long points.

Aquarius_Girl · 07-10-2012, 03:19 AM

Thanks for helping.

I will be knowing the location of the points on the map, and that'll be an area
sized much smaller than a pea.
But, inside that area, I won't be able to tell the "exact" point.
Will that library help in that casE?

graemef · 07-10-2012, 03:24 AM

You should be able to use it to convert the data from an image to true text and progress from there. I've not used the library in a while but the concept remains the same: convert from image to text; then validate the text; if it looks reasonable then use the result as your data.

theNbomr · 07-11-2012, 09:38 AM

If you know the type of projection of the map, it should be possible to calculate latitude and longitude corresponding to any pixel in the image based on the geometry of the mapping. It might be tricky to compute the mapping for many projection types. The field of cartography must have plenty of such software.
--- rod.

Aquarius_Girl · 07-11-2012, 10:00 AM

Well I was referring to this kind of BMP/PNG file:
http://maps.googleapis.com/maps/api/...4&sensor=false

VisionIncision · 07-11-2012, 01:22 PM

Quote:

Originally Posted by theNbomr

If you know the type of projection of the map, it should be possible to calculate latitude and longitude corresponding to any pixel in the image based on the geometry of the mapping. It might be tricky to compute the mapping for many projection types. The field of cartography must have plenty of such software.
--- rod.

If he is using a static image, e.g. in a world map application then this is how I would do it.

TB0ne · 07-12-2012, 10:22 AM

Quote:

Originally Posted by Anisha Kaul

Thanks for helping.

I will be knowing the location of the points on the map, and that'll be an area sized much smaller than a pea.
But, inside that area, I won't be able to tell the "exact" point.
Will that library help in that casE?

Try this page:
http://www.movable-type.co.uk/scripts/latlong.html

I had to do this with a vector-type topological map in the past, and it was a bear. If you know the boundaries of the map section you're working with, you're in a better place, since from those, you can calculate the number of points in-between, and work out the position. The page I linked to has some Java examples of code to do what you're seeking, but there are other language implementations of those same formulas. Guessing you're wanting to do this on a web-page.

dugan · 07-12-2012, 01:16 PM

Quote:

Originally Posted by Anisha Kaul

Well I was referring to this kind of BMP/PNG file:
http://maps.googleapis.com/maps/api/...4&sensor=false

If you're using Google's Map API anyway, then why can't you use it to get the latitude and longitude?