Error(s) in re-building vignettes:
  ...
--- re-building ‘extract_volcano_plume_tutorial.Rmd’ using rmarkdown
 ----------- FAILURE REPORT -------------- 
 --- failure: the condition has length > 1 ---
 --- srcref --- 
: 
 --- package (from environment) --- 
imagefx
 --- call from context --- 
fftshift(Re(x.filt))
 --- call from argument --- 
if (class(x) == "matrix") {
    rd2 <- floor(nrow(x)/2)
    cd2 <- floor(ncol(x)/2)
    q1 <- x[1:rd2, 1:cd2]
    q2 <- x[1:rd2, (cd2 + 1):ncol(x)]
    q3 <- x[(rd2 + 1):nrow(x), (cd2 + 1):ncol(x)]
    q4 <- x[(rd2 + 1):nrow(x), 1:cd2]
    centered.t <- rbind(q4, q1)
    centered.b <- rbind(q3, q2)
    centered <- cbind(centered.b, centered.t)
    return(Re(centered))
}
 --- R stacktrace ---
where 1: fftshift(Re(x.filt))
where 2: filt3d(img, gaus)
where 3: blob.extract(img.r.dtrend, max.r, win.size, gaus)
where 4: eval(expr, envir, enclos)
where 5: eval(expr, envir, enclos)
where 6: withVisible(eval(expr, envir, enclos))
where 7: withCallingHandlers(withVisible(eval(expr, envir, enclos)), warning = wHandler, 
    error = eHandler, message = mHandler)
where 8: handle(ev <- withCallingHandlers(withVisible(eval(expr, envir, 
    enclos)), warning = wHandler, error = eHandler, message = mHandler))
where 9: timing_fn(handle(ev <- withCallingHandlers(withVisible(eval(expr, 
    envir, enclos)), warning = wHandler, error = eHandler, message = mHandler)))
where 10: evaluate_call(expr, parsed$src[[i]], envir = envir, enclos = enclos, 
    debug = debug, last = i == length(out), use_try = stop_on_error != 
        2L, keep_warning = keep_warning, keep_message = keep_message, 
    output_handler = output_handler, include_timing = include_timing)
where 11: evaluate::evaluate(...)
where 12: evaluate(code, envir = env, new_device = FALSE, keep_warning = !isFALSE(options$warning), 
    keep_message = !isFALSE(options$message), stop_on_error = if (options$error && 
        options$include) 0L else 2L, output_handler = knit_handlers(options$render, 
        options))
where 13: in_dir(input_dir(), evaluate(code, envir = env, new_device = FALSE, 
    keep_warning = !isFALSE(options$warning), keep_message = !isFALSE(options$message), 
    stop_on_error = if (options$error && options$include) 0L else 2L, 
    output_handler = knit_handlers(options$render, options)))
where 14: block_exec(params)
where 15: call_block(x)
where 16: process_group.block(group)
where 17: process_group(group)
where 18: withCallingHandlers(if (tangle) process_tangle(group) else process_group(group), 
    error = function(e) {
        setwd(wd)
        cat(res, sep = "\n", file = output %n% "")
        message("Quitting from lines ", paste(current_lines(i), 
            collapse = "-"), " (", knit_concord$get("infile"), 
            ") ")
    })
where 19: process_file(text, output)
where 20: knitr::knit(knit_input, knit_output, envir = envir, quiet = quiet, 
    encoding = encoding)
where 21: rmarkdown::render(file, encoding = encoding, quiet = quiet, envir = globalenv(), 
    ...)
where 22: vweave_rmarkdown(...)
where 23: engine$weave(file, quiet = quiet, encoding = enc)
where 24: doTryCatch(return(expr), name, parentenv, handler)
where 25: tryCatchOne(expr, names, parentenv, handlers[[1L]])
where 26: tryCatchList(expr, classes, parentenv, handlers)
where 27: tryCatch({
    engine$weave(file, quiet = quiet, encoding = enc)
    setwd(startdir)
    output <- find_vignette_product(name, by = "weave", engine = engine)
    if (!have.makefile && vignette_is_tex(output)) {
        texi2pdf(file = output, clean = FALSE, quiet = quiet)
        output <- find_vignette_product(name, by = "texi2pdf", 
            engine = engine)
    }
}, error = function(e) {
    OK <<- FALSE
    message(gettextf("Error: processing vignette '%s' failed with diagnostics:\n%s", 
        file, conditionMessage(e)))
})
where 28: tools:::.buildOneVignette("extract_volcano_plume_tutorial.Rmd", 
    "/home/hornik/tmp/R.check/r-devel-gcc/Work/PKGS/imagefx.Rcheck/vign_test/imagefx", 
    TRUE, FALSE, "extract_volcano_plume_tutorial", "UTF-8", "/home/hornik/tmp/scratch/RtmpJexqRA/file34c03c9ce992.rds")

 --- value of length: 2 type: logical ---
[1]  TRUE FALSE
 --- function from context --- 
function (x) 
{
    if (class(x) == "matrix") {
        rd2 <- floor(nrow(x)/2)
        cd2 <- floor(ncol(x)/2)
        q1 <- x[1:rd2, 1:cd2]
        q2 <- x[1:rd2, (cd2 + 1):ncol(x)]
        q3 <- x[(rd2 + 1):nrow(x), (cd2 + 1):ncol(x)]
        q4 <- x[(rd2 + 1):nrow(x), 1:cd2]
        centered.t <- rbind(q4, q1)
        centered.b <- rbind(q3, q2)
        centered <- cbind(centered.b, centered.t)
        return(Re(centered))
    }
}
<bytecode: 0x561a8b358910>
<environment: namespace:imagefx>
 --- function search by body ---
Function fftshift in namespace imagefx has this body.
 ----------- END OF FAILURE REPORT -------------- 
Fatal error: the condition has length > 1
--- re-building ‘optical_flow_tutorial.Rmd’ using rmarkdown
--- finished re-building ‘optical_flow_tutorial.Rmd’

SUMMARY: processing the following file failed:
  ‘extract_volcano_plume_tutorial.Rmd’

Error: Vignette re-building failed.
Execution halted