TOPCAT Full Download — Installation & Setup Tutorial

4. Advanced Joins & Matching

• Sky matching with tolerance: Use Joins → Sky Match to crossmatch catalogs by coordinate with an angular tolerance (arcsec). Choose nearest, best, or all matches depending on needs.
• Multi-key joins: When matching on non-positional keys, use Table → Joins and specify multiple matching columns to prevent ambiguous merges.
• Preserve provenance: In joins, enable the option to keep original table names as column prefixes to track source columns post-merge.

5. Custom Plotting Tricks

• High-density plots: For crowded datasets, use density or contour plotting (Graphics → Plane Plot → Density) to reveal structure otherwise lost in scatter plots.
• Color by expression: In plot config, set color to an expression (e.g., log10(FLUX)) to encode third-variable information.
• Multiple layer plotting: Add several layers (points, contours, vectors) in a single plot to combine different visualizations — handy for overlaying fits on data.

6. Scripting & Automation

• STILTS integration: Export your workflow to STILTS commands (from the GUI’s help or export options) to run large-batch jobs on the command line. Example STILTS for join:

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   ffON2NH02oMAcqyoh2UU MQCbz04ET5EljRmK3YpQ CPXAhl7VTkj2dHDyAYAf” data-copycode=“true” role=“button” aria-label=“Copy Code”>Copy CodeCopied
  stilts tmatch2 in1=cat1.vot in2=cat2.vot ifmt1=vot ifmt2=vot find=nearest values=RA,DEC params=1 

• Batch plotting: Use the plotting commands in STILTS to generate consistent, repeatable figures for many tables without opening TOPCAT.

7. Memory & Performance Optimization

• Use streaming for large files: For very large tables, use STILTS or TOPCAT’s streaming options to avoid loading full tables into RAM.
• Limit columns at import: Import only needed columns via the format-specific import dialogs to reduce memory footprint.
• Increase JVM heap when needed: For massive datasets, start TOPCAT with a larger heap:

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  java -Xmx8g -jar topcat.jar 

8. FITS/VOTable Handling Best Practices

• Preserve metadata: When writing VOTables or FITS, keep UCDs and units to maintain interoperability with other tools.
• Chunked FITS access: For large FITS tables, use tools that support random access rather than full reads; TOPCAT supports efficient FITS I/O when configured correctly.

9. Useful Preferences & Shortcuts

• Autosave views: Enable view presets in Graphics → Save/Restore for consistent multi-plot setups.
• Keyboard navigation: Use arrow keys and Shift/Ctrl for multi-row selections in table view; double-click headers to sort.

10. Troubleshooting & Validation

• Check table integrity: Use View → Metadata to confirm units, UCDs, and data types before analyses.
• Common pitfalls: Watch for string-number mixing, null value handling, and implicit unit mismatches; use explicit conversions and ISNULL checks in expressions.

Quick Reference Table: Useful Expressions

Use these tips to speed up analysis, reduce memory issues, and create publication-quality outputs with TOPCAT Full.