如何使用每个像素中的信息创建位图？

Question

I'm creating a google maps application on Android and I'm facing problem. I have elevation data in text format. It looks like this

longtitude latitude elevation
491222     163550   238.270000
491219     163551   242.130000
etc.

This elevation information is stored in grid of 10x10 meters. It means that for every 10 meters is an elevation value. This text is too large so that I could find there the information I need so I would want to create a bitmap with this information.

What I need to do is in certain moment to scan the elevation around my location. There can be a lot of points to be scanned so I want to make it quick. That's why I'm thinking about the bitmap.

I don't know if it's even possible but my idea is that there would be a bitmap of size of my text grid and in every pixel would be information about the elevation. So it should be like invisible map over the google map placed in the place according to coordinates and when I need to learn the elevation about my location, I would just look at these pixels and read the value of elevation.

Do you think that is possible to create such a bitmap? I have just this idea but no idea how to implement it. Eg how to store in it the elevation information, how to read that back, how to create the bitmap.. I would be very grateful for every advice, direction, source which you can give me. Thank you so much!

Answer 1

As color with red, green, blue and alpha (opacity/transparency). Start with all pixels transparent. and fill in the corresponding value as (R, G, B), non-transparent (the high eight bits. (Or an other convention for "not filled in."

RGB form the lower 24 bits of an integer.

Longitude and latitude to x and y

Elevation to integer less 0x01_00_00_00. And vice versa:

double elevation = 238.27;
int code = (int)(elevation * 100);
Color c = new Color(code); // BufferedImage uses int, so 'code' sufThat does not fices.
code = c.getRGB();
elevation = ((double)code) / 100;  

BufferedImage with setRGB(code) or so (there are different possibilities).

Use Oracles javadoc, by googling after BufferedImage and such.

To fill unused pixels do an avaraging, in a second BufferedImage. So as never to average to original pixels.

PS for my Netherlands elevation might be less than zero, so maybe + ... .

Answer 2

BufferedImage is not available in android but android.graphics.Bitmap can be used. Bitmap must be saved in lossless format (eg. PNG).

double[] elevations={238.27,242.1301,222,1};
int[] pixels = doublesToInts(elevations);

    //encoding
Bitmap bmp=Bitmap.createBitmap(2, 2, Config.ARGB_8888);
bmp.setPixels(pixels, 0, 2, 0, 0, 2, 2);
File file=new File(getCacheDir(),"bitmap.png");
try {
    FileOutputStream fos = new FileOutputStream(file);
    bmp.compress(CompressFormat.PNG, 100, fos);
    fos.close();
} catch (IOException e) {
    e.printStackTrace();
}

//decoding
Bitmap out=BitmapFactory.decodeFile(file.getPath());
if (out!=null)
{   
    int [] outPixels=new int[out.getWidth()*out.getHeight()];
    out.getPixels(outPixels, 0, out.getWidth(), 0, 0, out.getWidth(), out.getHeight());
    double[] outElevations=intsToDoubles(outPixels);
}

static int[] doublesToInts(double[] elevations)
{
    int[] out=new int[elevations.length];
    for (int i=0;i<elevations.length;i++)
    {
        int tmp=(int) (elevations[i]*1000000);          
        out[i]=0xFF000000|tmp>>8;
    }
    return out;
}
static double[] intsToDoubles(int[] pixels)
{
    double[] out=new double[pixels.length];
    for (int i=0;i<pixels.length;i++)
        out[i]=(pixels[i]<<8)/1000000.0;
    return out;
}