Mapping GPS Locations to A 2D U.S. Map

Programming Questions

maudlinof..

Mapping GPS Locations to A 2D U.S. Map

in Programming Questions • 2 years ago

I've been working on this problem for a good while. I'm trying to map GPS locations to a 2D United States map. I have this code:

int x;
int y;
PImage raster;
void setup() {
size(1000, 500);
ellipseMode(CENTER);
smooth();
String[] lines = loadStrings("csvgpscombined2.txt");
raster = loadImage("world_longlatwgs84.png");
image(raster, 0, 0);
for (int i = 0; i < lines.length; i++) {
String[] pieces = split(lines[i], ",");
if (pieces.length == 2) {
float mapX = float(pieces[0]);
float mapY = float(pieces[1]);
println(mapX + " " + mapY);
x = int(((180+mapY)/360)*width);
y = int(height - ((90+mapX)/180)*height);
ellipse(x, y, 10, 10);
}
}
}

which plots a comma separated list of GPS locations on a world map 2D projection. I've been searching for a method to plot these points while only showing the continental U.S. I've read through Ben Fry's methodology on the subject and tried to rebuild what he had and I screwed up along the way. I'm very new to programming in general. I think I will be able to do this if I change this part of the code somehow:

x = int(((180+mapY)/360)*width);

y = int(height - ((90+mapX)/180)*height);

I'm really running out of ideas though. I've tried many different things. If anyone has any solution to this problem, it would be wonderful.

Replies(9)

theprof

Re: Mapping GPS Locations to A 2D U.S. Map

2 years ago

Hello, plotting the gps point is done using the map() function. If you can post a sample of your gps text file I can show you how to do it.

Basically, specify your bounds:

Go to http://itouchmap.com/latlong.html and get the upper and lower gps bounds you want to use in your map

// Map coordinate (start and end points)
float w_start; // Longtitude start (largest longitude value)
float w_end; // Longtitude end (smallest longitude value)
float h_start; // Latitude start (largest latitude value)
float h_end; // Latitude end (smallest latitude value)

mapX1 = 0;
mapX2 = width;
mapY1 = 0;
mapY2 = height;

For each point x and y in gps coordinates, to convert to pixel values use:
x = map(x, w_start, w_end, mapX1, mapX2);
y = map(y, h_end, h_start, mapY1, mapY2);

maudlinof..

Re: Mapping GPS Locations to A 2D U.S. Map

2 years ago

Thank you for the reply!

Here is a sampling of the GPS list:

30.504383,-97.62202

38.903832,-77.040211

38.85538,-77.065546

38.778011,-90.623047

38.535375,-121.503443

38.592359,-121.548397

38.778552,-77.269287

42.501644,-71.155848

EDIT:

Oh right, the bounds I want to use are :

24.52^o N latitude to 49.38^o N latitude.

66.95^oW longitude to 124.77^o W longitude.

The geographic center is near 39.8^o N latitude, 98.5^o W longitude. (not sure if that helps)

theprof

Re: Mapping GPS Locations to A 2D U.S. Map

2 years ago

Could you convert your bounds to decimal format for me please? Is your first column latitude or longitude? (I'm not from the US so I can't tell without checking google maps).

maudlinof..

Re: Mapping GPS Locations to A 2D U.S. Map

2 years ago

The bounds in degrees are:

24.52 and 49.38 north latitude.

66.95 and 124.77 degrees west longitude.

The first column is latitude and the second column is longitude.

Thank you so much for helping me with this!

maudlinof..

Re: Mapping GPS Locations to A 2D U.S. Map

2 years ago

I still need help with this!

float x;
float y;
//PImage raster;
void setup() {
size(1000, 500);
ellipseMode(CENTER);
smooth();
String[] lines = loadStrings("csvgpscombined2.txt");
//raster = loadImage("world_longlatwgs84.png");
//image(raster, 0, 0);
for (int i = 0; i < lines.length; i++) {
String[] pieces = split(lines[i], ",");
if (pieces.length == 2) {
float mapX = float(pieces[0]);
float mapY = float(pieces[1]);
println(mapX + " " + mapY);
float w_start = -124.77; // Longtitude start (largest longitude value)
float w_end = -66.95; // Longtitude end (smallest longitude value)
float h_start = 49.38; // Latitude start (largest latitude value)
float h_end = 24.52; // Latitude end (smallest latitude value)
int mapX1 = 0;
int mapX2 = width;
int mapY1 = 0;
int mapY2 = height;
//x = int(((180+mapY)/360)*width);
//y = int(height - ((90+mapX)/180)*height);
x = map(mapY, w_start, w_end, mapX1, mapX2);
y = map(mapX, h_end, h_start, mapY1, mapY2);
ellipse(x, y, 10, 10);
}
}
}

I got some really weird output using this code. I'm not sure this will work...

theprof

Re: Mapping GPS Locations to A 2D U.S. Map

2 years ago

Hello - sorry for the late reply, I ran the code using the gps coordinates you gave earlier. You got the right idea - you read the text file and map the coordinates to certain bounds and display it on the screen and got the below output:

Your code works!

theprof

Re: Mapping GPS Locations to A 2D U.S. Map

2 years ago

Here's an example I made for my students that reads GPS points from a map of cities in Switzerland that shows you how to do this in an object oriented way, I'll be very happy to answer any questions you have on this thread. I've commented the code so hope it helps you.

My best advice for you right now is to learn more about processing by buying Daniel Shiffman's book. He talks about reading from a text file and using the map() function in there.

theprof

Re: Mapping GPS Locations to A 2D U.S. Map

2 years ago

The url for download is: http://dl.dropbox.com/u/17698604/swiss_cities.zip

taahl0

Re: Mapping GPS Locations to A 2D U.S. Map

3 months ago

Hello,

I'm sorry to dig out this old post but after many hours of searching, I can't still find my answer...

Does it work with very small area ? I'm working with data of the scale of one city so the boundaries are very close :

float w_start = -1.716957; // Longtitude start (largest longitude value)

float w_end = -1.571045; // Longtitude end (smallest longitude value)

float h_start = 48.149925; // Latitude start (largest latitude value)

float h_end = 48.075986; // Latitude end (smallest latitude value)

I don't understand why the map function returns very big values (like 58923.938 for pos_x and 622681.4 for pos_y), I guess maybe it's a precision problem but I didn't read anywhere that the map function is limited in range or precision.

Thanks for your help,

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