Map Merge for OziExplorer: Step-by-Step Guide to Combining MapsMap merging in OziExplorer is a practical skill for creating seamless, high-resolution map files from multiple scanned maps, tiles, or overlapping map sheets. This guide walks you through the process from preparation to final export, with tips to avoid common pitfalls and preserve accurate georeferencing.
Why merge maps for OziExplorer?
Merging maps lets you:
- Create large, continuous map areas from smaller sheets or tiles.
- Improve navigation and route planning by eliminating gaps and overlapped edges.
- Reduce clutter in OziExplorer by consolidating many small map files into fewer larger ones.
What you’ll need
- OziExplorer (installed) — desktop version for map editing and calibration.
- Source map images (scans, tiles, screenshots) in common formats (JPG, PNG, TIFF).
- Ground control points (GCPs) or existing world files/PRJ/TFW when available.
- Optional: image editing software (e.g., GIMP, Photoshop) for cropping, color correction, or stitching before importing.
Overview of the workflow
- Prepare source images (crop, correct orientation, adjust color).
- Calibrate each image in OziExplorer or ensure they have correct world files.
- Use OziExplorer’s Map Merge tool (or external stitching, then import) to combine images.
- Edit map boundaries, adjust overlapping areas, and verify control points.
- Export merged maps and associated calibration files.
Step 1 — Prepare source images
- Scan or export images at a consistent DPI; higher DPI gives better detail but larger files.
- Crop unnecessary borders or scanner artifacts. Keep a small overlap (10–20%) between adjacent sheets to help alignment.
- If brightness/contrast/color vary between sheets, perform basic corrections to minimize visible seams.
Tip: Save working copies in a lossless format (TIFF or PNG) while editing, then export final merged images as JPG if file size is a concern.
Step 2 — Calibrate (georeference) each image
You can either:
- Calibrate each sheet individually inside OziExplorer using known coordinates (latitude/longitude) or map grid intersections, or
- Provide accurate world files (TFW/PRJ) or georeferenced images.
To calibrate in OziExplorer:
- Open OziExplorer and load the image.
- Use the Map Calibration dialog to place at least three well-distributed control points per image (more for curved distortions). Prefer corners and recognizable features that appear on adjacent sheets.
- Enter accurate geographic coordinates for each point (lat/long or grid coordinates).
- Save the calibration (.map file) and check residuals — aim for low error values. If residuals are high, add more points or verify coordinates.
Tip: When adjacent sheets share features, try to use the same coordinate points on overlapping areas to improve alignment.
Step 3 — Merge maps: internal vs external approaches
There are two common approaches:
A. Merge inside OziExplorer (using built-in Map Merge)
- OziExplorer includes tools to combine multiple calibrated maps into a single map reference.
- Procedure (general):
- Ensure all maps are calibrated and saved in your OziExplorer Maps folder.
- Open the first (base) calibrated map in OziExplorer.
- Use the Map Merge or MapEdit features to add other calibrated maps, aligning by their calibration points.
- Adjust map order and visibility; resolve overlaps by choosing which map provides the visible area.
Limitations: The internal merge may not produce a single stitched image file; it often manages multiple map files as a set with combined coverage. This is suitable for navigation but not for producing a single raster image.
B. Merge externally (stitch images then import)
- Use an image-stitching tool (Hugin, ImageMagick, AutoStitch, or GIS software like QGIS) to create a single large raster, then georeference that raster in OziExplorer.
- Workflow:
- Stitch the images in an external tool, preserving original resolution and georeferenced relationships where possible.
- Export the stitched image as a big TIFF/PNG/JPG.
- Import the stitched image into OziExplorer and create a new calibration (.map) using control points or by transforming existing calibration points from source sheets.
Advantage: Produces one consolidated image file suitable for other GIS tools and easier transfer between devices.
Step 4 — Align and refine overlaps
- If working within OziExplorer, check overlapping zones carefully. Zoom in and toggle between maps to inspect seam alignment.
- If stitching externally, ensure control points from the original sheets transfer correctly; re-check several points across the stitched image for drift.
- For areas with clear mismatches, add or adjust control points and re-run the transformation until residuals are acceptable.
Step 5 — Optimize and export
- Reduce file size for use on mobile devices by resampling or exporting to JPEG at a quality level that preserves legibility. Consider creating multiple zoom-tier maps (high-resolution for close-in use, lower for overview).
- Save and backup calibration files (.map) and any world files. OziExplorer requires these to position the map correctly.
- Test the merged map in OziExplorer by loading it, switching coordinate displays, and running a short route to ensure positioning matches reality.
Troubleshooting common problems
- Misaligned seams: Check calibration points in overlapping areas; increase their number and distribution.
- Different color/brightness across sheets: Pre-process images to match histograms or use color correction.
- Very large stitched image causes performance issues: Split map into tiles at sensible sizes (e.g., 2048–4096 px per side) and use multiple maps in OziExplorer, or create lower-resolution overview maps.
- High calibration residuals: Re-check coordinate accuracy, use more control points, and avoid points clustered in a small area.
Best practices & tips
- Use at least 4–6 well-distributed control points per sheet where possible.
- Keep overlap between adjacent maps to help matching features.
- Maintain a project directory with originals, edited images, stitched outputs, and associated .map/.tfw files.
- For mobile use, pre-generate map tiles at appropriate zoom levels to avoid runtime resampling.
- Consider QGIS for advanced mosaicking and georeferencing before bringing the result into OziExplorer.
Quick checklist
- [ ] Source images cropped and color-corrected
- [ ] Each image calibrated or has valid world files
- [ ] Stitch externally if you need a single raster file; otherwise merge in OziExplorer for navigation coverage
- [ ] Verify seams and residuals, adjust control points as needed
- [ ] Export backups and optimized versions for target devices
If you want, I can:
- Provide step-by-step commands for stitching in ImageMagick or Hugin, or
- Walk through calibration in OziExplorer with screenshots (you’d need to tell me which OziExplorer version you use).
Leave a Reply