Hi,
I am in the process of making a device that will fire a camera based on gps location. this camera firing device will take a starting gps coordinate and measure from that point to a set distance and then take a picture. this will be on a plane going almost 200mph taking pictures for google earth. i need a gps module that will be fairly accurate at that kind of speed. altitude doesn't matter it is just measuring distance. this is also only a prototype but i need it as accurate as possible for a reasonable price. any suggestions?
200 MPH = 294 feet per second
Use a 10 update per second GPS to get approx a 30 foot horiz resolution after lock. Of course, the RMS value will still have an error within the range of the GPS lock accuracy. You will likely need a Due to process the GPS serial stream... An 8MHz 328P will barely keep up with 1 cycle update using the standard GPS lib.
I have looked at several boards such as the adafruit ultimate gps module. some of which had an even faster update (up to 30 per second). any input on particular modules? i have already considered the need for a better board than say an uno, but will the mega do the trick? not opposed to the due but the mega is older and has less bugs from what i have read. also i need the gps to be accurate to about 2 meters at the most.
i found this module. would a due handle this? https://www.tindie.com/products/smokingresistor/s1216f8-gps-board-with-50-hz-update-rate/
i have already considered the need for a better board than say an uno, but will the mega do the trick? not opposed to the due but the mega is older and has less bugs from what i have read.
What definition of "better" are you using? The Mega has more memory, but is no faster than the Uno.
Calculating where you are, based on the GPS readings, the age of them, the direction you are going, and the speed you are traveling will need a fairly fast processor - faster than the Uno/Mega - I would think.
also i need the gps to be accurate to about 2 meters at the most
Why? Commercial GPS units are accurate to +/- 10 feet (about 3 meters). They tend to always err on the same side.I can't really imagine that taking a picture from altitude, traveling 200 mph, a foot or two one side or the other, is going to make that much difference.
i wasnt aware that the two boards were the same speed. i will definitely go with the due. and the pictures have to be pieced together for use with google earth so the more precise the location the better
Since it sound like you will be stitching the photos together and to so will probably have to register them and that will change the relative locations. Why not focus on getting an accurate location of about 1 out of 5 photos and integrate the pitot over time to get the distances for the four in between.
Time, latitude, longitude information in NMEA output is the instant at which GPS measurement is taken. It takes some time to formulate GPS solution from the measurement and output via UART, the delay depends on GPS internal processor speed and UART baud rate. By the time your Arduino decoded NMEA, gotten the location and have camera to take a picture, at 200mph that’s about 9 meters per 0.1 second, the latitude & longitude location you think you have for the photo will actually be off by the total processing delay involved. If the delay is 0.4 second, then the image will be off by about 36 meters. If you are taking image of a large zoom out area, off by 100 meter probably doesn’t matter. If it’s zoomed in image that needs high position accuracy, then position accuracy is affected by this processing delay. Choosing higher update rate receiver and highest possible baud rate would reduce this error, but you'll need a fast Arduino.
Another alternative is using rising edge of 1PPS signal to trigger interrupt to Arduino. For GPS running at 1Hz, most GPS take measurement at UTC second, which is at rising edge instant of 1PPS signal. There is only Arduino interrupt processing delay till camera is triggered to capture image. If you need to take picture higher than once per second, then precision timing GPS receiver which has programmable frequency generation phase locked to 1PPS might be useful. Such could generate 4Hz or 10Hz pulse synchronized to 1PPS for example, allowing triggering of your camera at higher rate and use 1Hz NMEA location received to interpolate the intermediate points. Interpolation of the intermediate points will have error if there is large acceleration, but should still give fair accuracy compared to other methods. Examples of precision timing mode receiver are LEA-6T or NS-T
If the time between photos is sufficient, you may consider using the heading and speed from the GPS to compute the location of the photo based on the time the photo was previously recorded.
Steps I envision...
Record a photo and the time it was taken.
Get the GPS heading, speed, and current time.
Compute the prior location of the photo from the current location.
You may add in computational/acquisition delays for computing prior photo location relative to aircraft speed.
Avoid using floating point.
Have I done this? No.