Workflow Guide adaptation of coordinates

All OCR-D processors are required to relate coordinates to the original image for each page, and to keep the original image reference (Page/@imageFilename). However, sometimes it may be necessary to deviate from that strict requirement in order to get the overall workflow to function properly.

For example, if you have a page-level dewarping step, it is currently impossible to correctly relate to the original image's coordinates for any segments annotated after that, because there is no descriptive annotation of the underlying coordinate transform in PAGE-XML. Therefore, it is better to replace the original image of the output PAGE-XML by the dewarped image before proceeding with the workflow. (If the dewarped image has also been cropped or deskewed, then of course all existing coordinates are re-calculated accordingly as well.)

Another use case is exporting PAGE-XML for tools that cannot apply cropping or deskewing, like LAREX or Transkribus.

Conversely, you might want to align two PAGE-XML files for the same page that have different original image references, projecting all segments below the page level from the one to the other (transforming all coordinates according to the page-level annotation, or keeping them unchanged).

Available processors

Processor	Parameter	Remarks	Call
ocrd-segment-replace-original			ocrd-segment-replace-original -I OCR-D-CROP-DESK -O OCR-D-CROP-DESK-SUBST
ocrd-segment-replace-page			ocrd-segment-replace-page -I OCR-D-CROP-DESK,OCR-D-CROP-DESK-SUBST-SEG -O OCR-D-CROP-DESK-SEG -P transform_coordinates true