# Choose the window. Keep the rest of the picture intentional.

Canonical: https://phasevoid.com/journal/projection-mapping-windows-and-walls/
Published: 2026-11-06. Updated: 2026-11-06.
By [Balance IT](https://balanceit.pl).
Category: Room mapping.

A window can use its wall for alignment without making that whole wall an output surface. The final map—not the room diagram—decides what receives a picture.

![Room-selection dialog with one window selected while both detected walls remain unselected](https://phasevoid.com/examples/room-scan/selection.png)

Actual selection UI with a synthetic two-wall room. One window is selected; the parent wall remains a calculation reference. This is not a photographed installation.



## A calculation reference is not an illuminated surface.

Start by choosing what should receive a visual. In the room selector, tap the detected window or choose its named checkbox. You can rotate the diagram and use the type filters when several surfaces overlap in the view. The list remains an alternative to precise tapping on a small shape. A visible wall in the diagram does not mean that wall has been selected for output.

A chosen window refers to its parent wall for alignment. Studio needs that relationship to place the window consistently inside the wall plane. It does not need to add the wall as another displayed region. Confirm the parent wall corners, then inspect the Review list before applying. If only Window 1 is selected, that is the new surface being added. The [scan-versus-calibration explanation](https://phasevoid.com/journal/room-scan-vs-projector-calibration/) separates those two roles.

This distinction also helps when discussing a setup with another operator. “Use this wall as the reference” and “put moving imagery across this wall” are different instructions. Name the intended surfaces and point to the final projector picture. An attractive room diagram is useful for selection, but the applied raster and a physical check decide whether the planned composition matches the room.

## Check what is already in the map before adding another region.

The review offers append or explicit replacement. Appending retains the existing mapped surfaces and their looks. That is useful for extending a calibrated setup, but it can also explain an unwanted background:an earlier Main screen or wall may still cover the full picture behind the newly selected window. Choosing only the window in the new scan draft does not silently delete an existing surface from the current map.

| Intended result | Review choice | Then inspect |
| --- | --- | --- |
| Only the new window region | Explicitly replace the current map when that is the intended change | No old full-frame surface remains in the applied list |
| Add a window to an existing setup | Append while keeping the current map | Existing surfaces still illuminate their earlier regions |
| Wall and window with different looks | Select both deliberately | Surface order, overlap, opacity and the actual result |
| Extend a crowded map | Stay within eight final surfaces | Choose fewer additions or explicitly review replacement |

Mapping Undo restores the earlier map after Apply. Use it as recovery for a deliberate edit, not as the only backup of a complete show. Keep a saved map or session before changing an established installation. If you revisit this same room later, the meaning of append is still “keep what is already here,”not “rebuild only the current selection.” Check names and counts rather than relying on a thumbnail.

When the wall and its window are both selected, their regions overlap by design. The added child surface is placed after its selected parent in the new group. Existing blend modes, opacity, masks and ordering can still change the visible result. If the window should have another world or effect, select that exact surface before editing it. Several regions share one final projector raster; they are not independent physical projector feeds.

## Separate the position of the region from what plays inside it.

A surface can follow Program, the complete composed picture, or use an independent procedural world and its own look and Surface FX. Program may include the main world, video layers, text and global effects. An independent surface has a different source scope. If changing the main world does not change a particular window, first check whether that surface uses Program or its own world. This is routing, not a failed corner edit.

Likewise, a correctly placed outline can contain an unexpected crop or effect. Source crop chooses part of the source image; the quad places that source on the output; the mask controls the region inside it. Do not move physical calibration corners simply to compensate for the wrong visual source. Use All controls when you need those details. The existing [surface-source guide](https://phasevoid.com/guides/projection-mapping/#surface-sources) owns the complete operational procedure.

- Confirm the intended surfaces and the actual append/replace choice.
- Align the necessary parent walls and inspect the final output after Apply.
- Select one named surface, then choose Program or an independent world and tune its FX.
- Rehearse the actual sound and projection arrangement, and save a recoverable map or session.

Public Studio tools remain free, and manual surfaces remain available when a scan is unsuitable. Native iPhone capture still needs the separate signed scanner build and device verification; the browser currently opens saved RoomPlan JSON. For the next visit, read [which room-mapping file to save](https://phasevoid.com/journal/save-room-scan-map-session/). It distinguishes the original scan from the derived map and the wider Studio setup.

## Try the idea

[Open Mapping with my setup kept](https://phasevoid.com/studio/?panel=mapping). Opening this task starts no audio, selects no file and grants no input permissions. Review the controls before changing the show.

## Related articles

- [A cue recalls a picture. Plan the music separately.](https://phasevoid.com/journal/vj-cues-vs-playlists/)
- [Save the settings. Keep the original media.](https://phasevoid.com/journal/save-vj-show-local-media/)
- [Rehearse the recovery as well as the drop.](https://phasevoid.com/journal/live-visual-show-rehearsal/)
- [A room scan finds surfaces. Alignment places the picture.](https://phasevoid.com/journal/room-scan-vs-projector-calibration/)
- [Save the room reference, the mapped picture, and the show deliberately.](https://phasevoid.com/journal/save-room-scan-map-session/)
- [A picture on the wall. A different job from lighting the room.](https://phasevoid.com/journal/projector-visuals-vs-event-lighting/)
- [Hand over a room someone else can actually operate.](https://phasevoid.com/journal/visual-room-handover/)
- [Choose the sound your video actually contains.](https://phasevoid.com/journal/music-visualizer-video-soundtrack/)
- [Choose a video file your destination can use.](https://phasevoid.com/journal/mp4-vs-webm-music-visualizer/)
- [Sound-reactive is not the same as beat-synced.](https://phasevoid.com/journal/audio-reactive-vs-beat-sync/)
- [Many surfaces. One projector picture.](https://phasevoid.com/journal/one-projector-many-visuals/)
- [The preview is not the finished film.](https://phasevoid.com/journal/preview-vs-rendered-video/)

[Journal](https://phasevoid.com/journal/) · [Operational guides](https://phasevoid.com/guides/)


## Continue your reading path

### Map and keep a room setup

Separate scan geometry from physical alignment, choose walls or windows deliberately, then save the right record for the next visit.

1. [A room scan finds surfaces. Alignment places the picture.](https://phasevoid.com/journal/room-scan-vs-projector-calibration/). Understand which geometry the scan provides and what the projector still needs.
2. [Choose the window. Keep the rest of the picture intentional.](https://phasevoid.com/journal/projection-mapping-windows-and-walls/) — this article. Select the intended regions and check overlap with existing surfaces.
3. [Save the room reference, the mapped picture, and the show deliberately.](https://phasevoid.com/journal/save-room-scan-map-session/). Keep the scan, derived map and Studio session for their different recovery jobs.

Open Mapping, select the intended scan or manual surfaces, check parent-wall alignment and review the final map. Save the appropriate scan, map or full session; native iPhone capture and physical acceptance remain separate.

[Working guide](https://phasevoid.com/guides/projection-mapping/#room-scan) · [Studio workspace](https://phasevoid.com/studio/?panel=mapping) · [This reading path](https://phasevoid.com/journal/#room-mapping)