Match Tesseract-OCR results to .uzn regions - tesseract

Question

When specifying the regions using a .uzn file, is there a way to then match the text output to the .uzn region where the text came from?

Answer 1

I found a way to do it by getting the bounding boxes for each character, and using that information to see which region every character belongs to.
// Load the .box file output by Tesseract-OCR, and match each bounding box
// to a character from the text. This is not trivial, because whitespaces
// are present in the text from the .txt, but are missing from the .box
// file.
std::vector<RECT> loadBoxFile(const wchar_t *fileName, const std::wstring &text, int imageHeight)
{
// Open file.
std::ifstream st(fileName);
if (!st.is_open())
throw std::runtime_error("Could not open .box file.");
std::string line;
std::string symbolAscii;
std::wstring symbol;
RECT r = { -1, -1, -1, -1 };
std::vector<RECT> ret;
ret.resize(text.size(), r);
size_t textPos = 0;
while (std::getline(st, line)) {
// Parse a line.
std::istringstream iss(line);
if (!(iss >> symbolAscii >> r.left >> r.top >> r.right >> r.bottom))
throw std::runtime_error("Could not parse .box file line.");
symbol = utf8to16(symbolAscii.c_str());
// We don't try to get the bounding box for '~', because sometimes
// there is a '~' in .box file that is not there in .txt file. It's
// a bug in Tesseract-OCR as far as I know. This is a workaround
// for that case.
if (L"~" == symbol)
continue;
// Now match the symbol for that line to a symbol in the .txt file.
textPos = text.find(symbol, textPos);
// If we couldn't match it then fail.
if (text.npos == textPos)
throw std::runtime_error(std::string() + "Could not match symbol \"" + symbolAscii + "\" from .box file to .txt file.");
// Write the bounding box in the array, at index matching the symbol
// in the .txt file.
r.bottom = imageHeight - r.bottom;
r.top = imageHeight - r.top;
for (int ii = 0; ii < symbol.size(); ii++)
ret[textPos + ii] = r;
// Now increment textPos() so we start searching after the last
// symbol of the currently found symbol.
textPos += symbol.size();
}
return ret;
}