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1		-XWiki.AISOPAdmin
	1	+XWiki.andisk

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57	57	* The least amount of content to be extracted is the complete set of slides and their comments. We recommend to use past students' e-portfolios too. We had rather good experience with about 1000 fragments for a course.
58	58	* If interrupted, the process may create several JSON files. You can combine them using the [[merge-tool>>https://gitlab.com/aisop/aisop-hacking/-/tree/main/merge-json-files]].
59	59
	60	+
	61	+==== 1.2.1: Extract Text from PDF or PNG (PDF → PNG → Text) ====
	62	+
	63	+Text extraction from PDFs is sometimes faulty. Additionally, many PDFs contain images. To capture this text, Tesseract can be used. A brief explanation of how to use it is provided here.
	64	+
	65	+**Prerequisites**
	66	+
	67	+~1. Tesseract must be installed
	68	+
	69	+(% class="box" %)
	70	+(((
	71	+##tesseract ~-~-version##
	72	+)))
	73	+
	74	+2. Poppler must be installed
	75	+
	76	+(% class="box" %)
	77	+(((
	78	+##brew install poppler##
	79	+)))
	80	+
	81	+**Code**
	82	+
	83	+(% class="box" %)
	84	+(((
	85	+##for pdf in *.pdf; do
	86	+# Extract the base name of the PDF without the extension
	87	+basename="${pdf%.pdf}"
	88	+\\# Convert PDF to PNGs
	89	+pdftoppm -png "$pdf" "$basename"
	90	+\\# Create a text file with the same name as the PDF.
	91	+for png in "$basename"-*.png; do
	92	+ tesseract "$png" stdout -l deu ~-~-oem 1 | tr '~\~\n' ' ' | sed 's/  */ /g' >> "$basename.txt"
	93	+ echo -e "~\~\n~\~\n~-~--~\~\n~\~\n" >> "$basename.txt"
	94	+done
	95	+done
	96	+rm *.png##
	97	+)))
	98	+
	99	+**Explanation**
	100	+
	101	+~1. ##for pdf in *.pdf; do ...; done##
	102	+
	103	+• Loops through all PDF files in the directory.
	104	+
	105	+2. ##basename="${pdf%.pdf}"##
	106	+
	107	+• Extracts the filename of the PDF without the .pdf extension.
	108	+
	109	+3. ##pdftoppm -png "$pdf" "$basename"##
	110	+
	111	+• Converts the PDF into PNG images, named in the format BASENAME-1.png, BASENAME-2.png, etc.
	112	+
	113	+4. ##for png in "$basename"-*.png; do ...; done##
	114	+
	115	+• Processes only the PNG files generated from the current PDF.
	116	+
	117	+5. ##tesseract "$png" stdout -l deu ~-~-oem 1##
	118	+
	119	+• Performs OCR on the PNG file.
	120	+
	121	+6. ##tr '\n' ' '##
	122	+
	123	+• Replaces line breaks with spaces.
	124	+
	125	+7. ##sed 's/  */ /g'##
	126	+
	127	+• Reduces multiple spaces to a single space.
	128	+
	129	+8. ##>> "$basename.txt"##
	130	+
	131	+• Appends the recognized text to a text file with the same name as the PDF.
	132	+
	133	+9. ##echo -e "\n\n~-~--\n\n" >> "$basename.txt"##
	134	+
	135	+• Adds a separator line (~-~--) after each page.
	136	+
	137	+**Result**
	138	+
	139	+• A separate text file is created for each PDF, e.g.:
	140	+
	141	+• file1.txt for file1.pdf
	142	+
	143	+• file2.txt for file2.pdf
	144	+
	145	+• The OCR results of all pages from the respective PDF are written into this text file.
	146	+
	147	+• Each page is separated by a separator line (~-~--).
	148	+
	149	+• Temporary PNG files are deleted at the end.
	150	+
60	60	=== 1.3: Annotate Text Fragments ===
61	61
62	62	It is time to endow the fragments with topics so that we can recognize students' paragraphs' topics. In AISOP, we have used the (commercial) [[prodigy>>https://prodi.gy/]] for this task in two steps which, both, iterate through all fragments to give them topics.