Cannot move camera using libuvc - c

Question

I'm trying to control my camera using libuvc.
I tried this code I modified from the example:
#include <libuvc/libuvc.h>
#include <stdio.h>
#include <unistd.h>
int main() {
uvc_context_t *ctx;
uvc_device_t *dev;
uvc_device_handle_t *devh;
uvc_stream_ctrl_t ctrl;
uvc_error_t res;
/* Initialize a UVC service context. Libuvc will set up its own libusb
* context. Replace NULL with a libusb_context pointer to run libuvc
* from an existing libusb context. */
res = uvc_init(&ctx, NULL);
if (res < 0) {
uvc_perror(res, "uvc_init");
return res;
}
puts("UVC initialized");
/* Locates the first attached UVC device, stores in dev */
res = uvc_find_device(
ctx, &dev,
0, 0, NULL); /* filter devices: vendor_id, product_id, "serial_num" */
if (res < 0) {
uvc_perror(res, "uvc_find_device"); /* no devices found */
} else {
puts("Device found");
/* Try to open the device: requires exclusive access */
res = uvc_open(dev, &devh);
if (res < 0) {
uvc_perror(res, "uvc_open"); /* unable to open device */
} else {
puts("Device opened");
uvc_print_diag(devh, stderr);
//uvc_set_pantilt_abs(devh, 100, 100);
int result = uvc_set_pantilt_abs(devh, 5, 50);
printf("%d\n", result);
//sleep(5);
/* Release our handle on the device */
uvc_close(devh);
puts("Device closed");
}
/* Release the device descriptor */
uvc_unref_device(dev);
}
/* Close the UVC context. This closes and cleans up any existing device handles,
* and it closes the libusb context if one was not provided. */
uvc_exit(ctx);
puts("UVC exited");
return 0;
}
I tried both uvc_set_pantilt_abs and uvc_set_pantilt_rel and both are returning 0 so it means the action is successful. Except the camera does not move.
I'm sure the camera uses UVC because uvc_print_diag indicates
VideoControl:
bcdUVC: 0x0110
Am I doing something wrong? If not how can I troubleshoot it?

Answer 1

I found the answer a while ago but forgot to put it here.
I stumbled upon this project which controls a camera using a commandline tool with libuvc.
After playing a bit with it and compared it with my code I got what I did wrong. He was getting the pantilt data from the camera and then using it to send requests. It seems cameras need to receive a number which must be a multiple of the "step" provided by the camera as the movement unit.
Here's the part where he requests the pantilt information:
int32_t pan;
int32_t panStep;
int32_t panMin;
int32_t panMax;
int32_t tilt;
int32_t tiltStep;
int32_t tiltMin;
int32_t tiltMax;
// get current value
errorCode = uvc_get_pantilt_abs(devh, &pan, &tilt, UVC_GET_CUR);
handleError(errorCode, "Failed to read pan/tilt settings - possibly unsupported by this camera?\n");
// get steps
errorCode = uvc_get_pantilt_abs(devh, &panStep, &tiltStep, UVC_GET_RES);
handleError(errorCode, "Failed to read pan/tilt settings - possibly unsupported by this camera?\n");
// get min
errorCode = uvc_get_pantilt_abs(devh, &panMin, &tiltMin, UVC_GET_MIN);
handleError(errorCode, "Failed to read pan/tilt settings - possibly unsupported by this camera?\n");
// get max
errorCode = uvc_get_pantilt_abs(devh, &panMax, &tiltMax, UVC_GET_MAX);
handleError(errorCode, "Failed to read pan/tilt settings - possibly unsupported by this camera?\n");
Here's the full code