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1		-XWiki.andisk
	1	+XWiki.AISOPAdmin

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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		-
151	151	=== 1.3: Annotate Text Fragments ===
152	152
153	153	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.