Simultaneously reading and writing from file

dwarrenku

Simultaneously reading and writing from file

in Contributed Library Questions • 5 months ago

There are surely a million different problems in this sketch, but go easy since it's my first try at processing (and java). If you find more than what this post is about, let me know. I'll appreciate any help.

Like a previous post, this sketch is meant to plot the position of a high altitude balloon transmitting it's position from an xbee. The string the xbee receives is saved using a serial capture to a file, and this sketch reads in each line using BufferedReader. The problem is the sketch tries to load the file when there's a partial string, leading to an error. Is there a way to force it to wait until the string has loaded?

Here's a sample of the transmitted data:

!!!47.6696,-71.4853,0.16,249.91,162.50,6

!!!47.6696,-71.4853,0.45,249.91,162.50,6

Here's the sketch, and the throw message is below:

BufferedReader reader;
import googlemapper.*;
import controlP5.*;
double mapCenterLat = 42.66656;
double mapCenterLon = -72.4831;
int zoomLevel =10;
String mapType = GoogleMapper.MAPTYPE_ROADMAP;
int mapWidth=640;
int mapHeight=480;
String inBuffer;
Boolean isGPSActive;
ArrayList<Double> lat = new ArrayList<Double>();
ArrayList<Double> lng = new ArrayList<Double>();
Double newLat;
Double newLng;
float cent_lat = 0;
float cent_lng = 0;
int x;
ControlP5 cp5;
int zoomSlider=15;
Slider abc;
PImage map;
GoogleMapper gMapper;
public void setup() {
//start reading the file with fake info
reader = createReader("serialcapture.txt");
//sets the window size to 640x480
size(640, 480);
smooth();
//creates new controls using the P5 Library
cp5 = new ControlP5(this);
cp5.addSlider("zoomSlider")
.setPosition(50, 100)
.setSize(40, 200)
.setRange(3, 21)
.setNumberOfTickMarks(18);
cp5.addButton("refresh")
.setValue(0)
.setPosition(50, 80)
.setSize(40, 19);
//sets the zoomlevel
zoomLevel=zoomSlider;
}
long interval = millis();
//function to run when refresh button is pressed
void refresh() {
loop();
println("refreshing map");
try {
interval = millis();
zoomLevel=zoomSlider;
if (cent_lat != 0) {
mapCenterLat = gMapper.y2lat(cent_lat);
mapCenterLon = gMapper.x2lon(cent_lng);
}
gMapper = new GoogleMapper(mapCenterLat, mapCenterLon, zoomLevel, mapType, mapWidth, mapHeight);
map = gMapper.getMap();
image(map, 0, 0);
lat.clear();
lng.clear();
reader.close();
reader = createReader("serialcapture.txt");
inBuffer = reader.readLine();
drawcourse(inBuffer);
cent_lat = 0;
cent_lng = 0;
}
catch(Exception e) {
e.printStackTrace();
}
x=0;
}
void draw() {
inBuffer = null;
//reads the data from the serial and stores it in a buffer
if (mousePressed && keyPressed) {
if (key == 'c' || key == 'C') {
cent_lat = mouseY;
cent_lng = mouseX;
}
}
try {
inBuffer = reader.readLine();
}
catch (IOException e) {
e.printStackTrace();
inBuffer = null;
delay(250);
}
if (inBuffer != null) {
drawcourse(inBuffer);
}
else return;
}
void drawcourse(String inBuffer) {
//*****display iteration in top left
background(0);
image(map, 0, 0);
fill(0);
textSize(16);
text("position: "+x, 10, 20);
x++;
inBuffer = inBuffer.substring(3);
//println(inBuffer);//for debugging inBuffer read
String[] op = inBuffer.split(",");
//only when we get valid data, split it to get coordinates
if (op.length==6) {
newLat = Double.valueOf(op[0]); //get latitude
newLng = Double.valueOf(op[1]); //get longitude
lat.add(newLat.doubleValue());
lng.add(newLng.doubleValue());
isGPSActive=true;
}
for (int i=1; i < lat.size()-1 ; i++)
{
if (lat.get(i)==null) return;
else {
float lat1 = (float) gMapper.lat2y(lat.get(i));
float lng1 = (float) gMapper.lon2x(lng.get(i));
float lat2 = (float) gMapper.lat2y(lat.get(i+1));
float lng2 = (float) gMapper.lon2x(lng.get(i+1));
stroke(0);
strokeWeight(2);
line(lng1, lat1, lng2, lat2);//draws the latest position on the screen
//ellipse(lng2, lat2, 5, 5);
//println(lat1+"-"+lng1+"|"+lat2+"-"+lng2);//debug output to see line positions
}
}
}

Error message:

Exception in thread "Animation Thread" java.lang.StringIndexOutOfBoundsException: String index out of range: -1
at java.lang.String.substring(String.java:1937)
at java.lang.String.substring(String.java:1904)
at googlemapper_testing__01.drawcourse(googlemapper_testing__01.java:135)
at googlemapper_testing__01.draw(googlemapper_testing__01.java:120)
at processing.core.PApplet.handleDraw(PApplet.java:2266)
at processing.core.PGraphicsJava2D.requestDraw(PGraphicsJava2D.java:243)
at processing.core.PApplet.run(PApplet.java:2140)
at java.lang.Thread.run(Thread.java:680)

Replies(3)

PhiLho

Re: Simultaneously reading and writing from file

5 months ago

General remark: put size() at the top of your setup().
Avoid doing I/O before it!

Are you sure it is an issue with reading a "partial string" (whatever it can be!).
Which line is highlighted? (since we cannot run your code. BTW, moved from Programming Questions, because of the requirements to run the sketch.)
Looks like you are trying to do a substring() with a negative index, so you better check the values you pass to this function.

dwarrenku

Re: Simultaneously reading and writing from file

5 months ago

Thanks PhiLho for the reply and moderation.

Line 115 was the offending line, which is what lead me to believe that it was bringing in a partial string before the capture was finished. I changed line 99 to the following and it seems to have solved the issue:

if (inBuffer != null && inBuffer.length()>20)

The sketch now seems to run fine, but I have one other general question. Does refresh automatically run before the draw loop starts because it's placed before draw? This could be a dumb question, but I'm learning.

GoToLoop

Re: Simultaneously reading and writing from file

5 months ago

Does refresh() automatically run before the draw() loop starts because it's placed before draw()?

Nope! All of your functions belong to the sketch itself.

And that's not what determines their order of execution call.

Processing always calls draw() 1st. Then any events triggered while draw() was running

are queued up to happen only after it's finished and the screen refreshed!

Function refresh() is registered to library controlP5.

And it's also callbacked after draw(); just like any other event functions!

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