Object Snapping & Precision Controls
Precision is non-negotiable in underground blast design. A collar offset of a few centimetres, compounded across a ring, can result in significant overbreak or underloading. BlastCAD’s precision engine — OSNAP, Polar Tracking, and direct coordinate input — eliminates guesswork from every drawing operation.
Table of contents
Object Snapping (OSNAP)
When a drawing tool is active, BlastCAD continuously analyses the scene geometry near your cursor. When the cursor approaches a snap candidate, a coloured marker appears with a tooltip identifying the snap type, and the cursor locks to that point.
Snap Modes
Toggle individual snap modes via the OSNAP settings panel in the Canvas Toolbar, or press F3 to toggle all snapping on/off.
| Snap Mode | Marker | Description |
|---|---|---|
| Endpoint | Square | Nearest start or end vertex of a line, polyline, or arc |
| Midpoint | Triangle | Exact center of a line segment or arc |
| Center | Circle | Center of a circle, arc, or donut |
| Node | X | A Point entity placed in the scene |
| Quadrant | Diamond | The 0°, 90°, 180°, or 270° point of a circle or arc |
| Intersection | X cross | The computed intersection of two entities (even if they don’t physically cross) |
| Perpendicular | Right angle | The point on an entity that forms a 90° angle with the previous point |
| Tangent | Tangent symbol | The point on a circle/arc where the line from the cursor is tangent |
| Nearest | Hourglass | The closest point on any entity (projected onto the entity’s curve) |
Snap Priority
When multiple snap candidates are simultaneously within snap range, BlastCAD prioritises them in this order:
- Endpoint
- Intersection
- Center
- Midpoint
- Quadrant
- Node
- Perpendicular / Tangent
- Nearest
Hold Tab while hovering to cycle through the available snap candidates at the cursor position.
Snap Aperture
The snap aperture (the radius within which snap candidates are detected) is proportional to the current zoom level. Zooming in tightens the aperture for more precise picking in dense geometry.
Polar Tracking
Polar tracking constrains the cursor to move along specific angle increments from the last point. When the cursor approaches a tracked angle, a dashed green line appears along the polar axis, and the cursor locks to that direction.
To enable: Click the Polar button in the Canvas Toolbar or press F10.
Preset Angles
| Setting | Tracked angles |
|---|---|
| 15° | 0, 15, 30, 45, 60, 75, 90, 105, 120, 135, 150, 165, 180, … |
| 30° | 0, 30, 60, 90, 120, 150, 180, … |
| 45° | 0, 45, 90, 135, 180, … |
| 90° | 0, 90, 180, 270 |
| Custom | Enter any angle increment (e.g., 22.5°) |
Direct Distance with Polar
When Polar tracking snaps to a direction, type a numeric distance and press Enter to place the next point exactly that distance along the tracked angle. This is the fastest way to draw lines of precise length at specific bearings.
Example: To draw a 5.5 m line at 45°:
- Click the start point.
- Move the cursor roughly northeast until the 45° polar axis snaps.
- Type
5.5and press Enter.
Ortho Mode
Ortho mode is the simplest precision constraint: it forces all cursor movement to be strictly horizontal (0°) or vertical (90°).
To enable: Click the Ortho button or press F8.
Ortho mode and Polar Tracking cannot be active simultaneously. Enabling one disables the other.
Grid
The grid is a visual reference overlay displayed in the viewport. It has two independent settings:
| Setting | Description |
|---|---|
| Grid Display | Shows the grid lines / dots (F7) |
| Grid Snap | Forces cursor to snap only to grid intersection points (F9) |
Set the grid size (spacing) in the Canvas Toolbar settings panel. For mine-scale work, a 1 m grid is standard; for detailed charge design views, 0.1 m may be more useful.
Coordinate Input
Explicit coordinate input always overrides snap and tracking. While a drawing tool is active, type coordinates into the canvas and press Enter.
Formats
| Format | Description | Example |
|---|---|---|
X,Y | Absolute 2D | 100,50 |
X,Y,Z | Absolute 3D | 100,50,320 |
@dX,dY | Relative 2D from last point | @10,-5 |
@dX,dY,dZ | Relative 3D from last point | @0,0,2.5 |
@dist<angle | Polar relative (2D) | @8.5<270 |
dist | Direct distance along polar/ortho axis | 12 |
Working with Large Mine Coordinates
Mine-site coordinates (e.g., Easting 432,500; Northing 7,350,000) are too large for single-precision floating-point arithmetic used in the WebGL renderer. BlastCAD solves this with a Global Origin:
- Open Project Settings from the top bar.
- Set the Global Origin to a representative local reference (e.g., the centroid of your survey area).
- All imported coordinates are automatically shifted by the origin offset.
- All exported coordinates are shifted back to world space.
Once the origin is set, type local coordinates directly in the Command Terminal — BlastCAD handles the transformation transparently.
Snap Override (One-Shot)
While in a drawing command, you can temporarily override the current snap mode for a single point pick by using snap overrides:
| Override Code | Snap Type |
|---|---|
END | Endpoint |
MID | Midpoint |
CEN | Center |
INT | Intersection |
PER | Perpendicular |
TAN | Tangent |
NEA | Nearest |
NON | None (disable snap for this pick only) |
Type the override code in the Command Terminal before clicking the point. The override applies only for the next single pick, then reverts to the configured snap modes.