OmniPage XML转ALTO XML开发：求SP标签WIDTH值计算公式

Hey there! Let's break down how to figure out the WIDTH value for ALTO XML's SP tag when converting from OmniPage XML— I’ve dealt with both formats enough to share some practical approaches:

Key Background to Start With #

First, remember that in ALTO XML, the SP (space) tag’s WIDTH represents the actual on-page pixel width of the whitespace character, just like the width of regular text characters. Since you’ve already aligned HPOS/VPOS using C#’s Rect class, you’re halfway there— the coordinate system alignment is already sorted, which is critical.

Possible Calculation Methods #

Here are the most reliable ways to derive the value:

• Use OmniPage’s Bounding Box Data Directly
  If your OmniPage XML includes bounding box coordinates for whitespace characters (some versions do, even if spaces are easy to overlook), simply convert that box to a C# Rect object. The Rect.Width property will directly map to the SP tag’s WIDTH value in ALTO. This is the most straightforward solution if the data exists.

• Calculate From Adjacent Character Positions
  If OmniPage doesn’t explicitly list bounding boxes for spaces, you can derive the width from the positions of the characters before and after the space:

  1. Grab the HPOS + WIDTH of the character immediately preceding the space (this gives the right edge of that character).
  2. Grab the HPOS of the character immediately following the space (this gives the left edge of that character).
  3. Subtract the two values: (NextChar.HPOS) - (PrevChar.HPOS + PrevChar.WIDTH) — this difference is the width of the space, which becomes your SP tag’s WIDTH.

• Leverage OmniPage’s Font/Spacing Parameters
  Some OmniPage XML variants include font metadata or character spacing attributes (look for nodes like <CharParams> or <Font>). If you find a space width ratio (e.g., relative to the font’s average character width), multiply that ratio by the font’s actual average pixel width (which you can get from either OmniPage’s data or the ALTO reference file you have) to get the SP width.

Quick Validation Tip #

Grab a test sample where you know the ALTO SP tag’s WIDTH value. Cross-reference this with the corresponding section in your OmniPage XML— reverse-engineering from a known value will help you confirm which method works for your specific OmniPage output version.

内容的提问来源于stack exchange，提问作者mecocopy