如何获取 PDF 内文本的位置/坐标？

Posted 2023-03-07

【中文标题】如何获取 PDF 内文本的位置/坐标？

【英文标题】：How to get the position / coordinates of an text inside of a PDF?

【发布时间】：2020-01-28 08:45:03

【问题描述】：

我目前正在开发一个 Ruby on Rails 应用程序，它将在特定位置插入图像。 但这个位置必须先确定。因此，我尝试确定文本“客户签名”和 PDF 中的相应位置。 用gem pdf-reader查找文本是没有问题的，但是如何获取这个文本的位置来绘制签名图像呢？

如果 gem pdf-reader 无法做到这一点，我也很感谢命令行程序的替代解决方案。

【问题讨论】：

你有没有这个问题（更重要的是，答案）：***.com/questions/22898145/…?

谢谢，这看起来非常好，尤其是在 Python 已经在使用的情况下。我已经在 Ruby 中找到了一个解决方案以及 pdf-reader gem：blog.peschla.net/2014/04/…

【参考方案1】：

我在这个网站上找到了我的问题的答案：http://blog.peschla.net/2014/04/parsing-pdf-text-with-coordinates-in-ruby/

它也适用于当前的 pdf-reader gem。

#! /usr/bin/ruby
require 'pdf-reader'

class CustomPageLayout < PDF::Reader::PageLayout
  attr_reader :runs

  # we need to filter duplicate characters which seem to be caused by shadowing
  def group_chars_into_runs(chars)
    # filter out duplicate chars before going on with regular logic,
    # seems to happen with shadowed text
    chars.uniq! |val| x: val.x, y: val.y, text: val.text
    super
  end
end

class PageTextReceiverKeepSpaces < PDF::Reader::PageTextReceiver
  # We must expose the characters and mediabox attributes to instantiate PageLayout
  attr_reader :characters, :mediabox

  private
  def internal_show_text(string)
    if @state.current_font.nil?
      raise PDF::Reader::MalformedPDFError, "current font is invalid"
    end
    glyphs = @state.current_font.unpack(string)
    glyphs.each_with_index do |glyph_code, index|
      # paint the current glyph
      newx, newy = @state.trm_transform(0,0)
      utf8_chars = @state.current_font.to_utf8(glyph_code)

      # apply to glyph displacment for the current glyph so the next
      # glyph will appear in the correct position
      glyph_width = @state.current_font.glyph_width(glyph_code) / 1000.0
      th = 1
      scaled_glyph_width = glyph_width * @state.font_size * th

      # modification to the original pdf-reader code which otherwise accidentally removes spaces in some cases
      # unless utf8_chars == SPACE
      @characters << PDF::Reader::TextRun.new(newx, newy, scaled_glyph_width, @state.font_size, utf8_chars)
      # end

      @state.process_glyph_displacement(glyph_width, 0, utf8_chars == SPACE)
    end
  end
end

class PDFTextProcessor
  MAX_KERNING_DISTANCE = 10 # experimental value

  # pages may specify which pages to actually parse (zero based)
  #   [0, 3] will process only the first and fourth page if present
  def self.process(pdf_io, pages = nil)
    pdf_io.rewind
    reader = PDF::Reader.new(pdf_io)
    fail 'Could not find any pages in the given document' if reader.pages.empty?
    processed_pages = []
    text_receiver = PageTextReceiverKeepSpaces.new
    requested_pages = pages ? reader.pages.values_at(*pages) : reader.pages
    requested_pages.each do |page|
      unless page.nil?
        page.walk(text_receiver)
        runs = CustomPageLayout.new(text_receiver.characters, text_receiver.mediabox).runs

        # sort text runs from top left to bottom right
        # read as: if both runs are on the same line first take the leftmost, else the uppermost - (0,0) is bottom left
        runs.sort! |r1, r2| r2.y == r1.y ? r1.x <=> r2.x : r2.y <=> r1.y

        # group runs by lines and merge those that are close to each other
        lines_hash = 
        runs.each do |run|
          lines_hash[run.y] ||= []
          # runs that are very close to each other are considered to belong to the same text "block"
          if lines_hash[run.y].empty? || (lines_hash[run.y].last.last.endx + MAX_KERNING_DISTANCE < run.x)
            lines_hash[run.y] << [run]
          else
            lines_hash[run.y].last << run
          end
        end
        lines = []
        lines_hash.each do |y, run_groups|
          lines << y: y, text_groups: []
          run_groups.each do |run_group|
            group_text = run_group.map  |run| run.text .join('').strip
            lines.last[:text_groups] << (
              x: run_group.first.x,
              width: run_group.last.endx - run_group.first.x,
              text: group_text,
            ) unless group_text.empty?
          end
        end
        # consistent indexing with pages param and reader.pages selection
        processed_pages << page: page.number, lines: lines
      end
    end
    processed_pages
  end
end

if File.exists?(ARGV[0])
  file = File.open(ARGV[0])
  pages = PDFTextProcessor.process(file)
  puts pages
  puts "Parsed #pages.count pages"
else
  puts "Cannot open file '#ARGV[0]' (or no file given)"
end

带有文本和坐标的示例输出：

  page: 1,
  lines: [
    
      y: 771.4006,
      text_groups: [
        x: 60.7191, width: 164.6489200000004, text: "Some text on the left",
        x: 414.8391, width: 119.76381600000008, text: "Some text on the right"
      ]
    ,
    
      y: 750.7606,
      text_groups: [x: 60.7191, width: 88.51979999999986, text: "More text"]
    
  ]