DXF Layer Alignments

When you do not have a LandXML file, SiteView can create a simplified alignment from a polyline layer in an uploaded DXF design surface. The polyline vertices are converted to straight-segment geometry, giving you chainage markers, cross-sections, and conformance checking without needing a full civil design export.

When to Use DXF Alignments

DXF layer alignments are a practical alternative when:

• Your design team has not provided a LandXML export but you have a DXF design file with the centreline drawn as a polyline.
• You need a quick, preliminary alignment for initial site checks before the formal design data arrives.
• The alignment is relatively straight or gently curving, so straight-segment approximation is adequate.
• You are working on a smaller project where the full precision of clothoid spiral geometry is not critical.

If you do have a LandXML file, the LandXML import is always the better option. LandXML captures the exact mathematical definition of curves and spirals, while a DXF polyline only provides vertices connected by straight lines.

ℹ️ Did you know?

A DXF-derived alignment is marked as "simplified" in SiteView. This flag is a reminder that the geometry consists of straight segments only — no curves or spirals. Chainage calculations along straight segments are exact, but the alignment path between vertices follows chord lines rather than true curve geometry.

Prerequisites

Before you can create a DXF layer alignment, you need:

1. An uploaded DXF design surface — the DXF file must already be uploaded to the site through the Design Surfaces feature. SiteView parses the DXF and makes its layers available for selection.
2. A suitable polyline layer — the DXF must contain at least one layer with line or polyline features that represents the centreline path. Only layers with line-type geometry appear in the layer selector.

Creating a DXF Layer Alignment

To create an alignment from a DXF layer:

1. Open a site in SiteView and navigate to the Alignments section.
2. Click Import Alignment to open the upload modal.
3. Select From DXF Layer as the source format.
4. Choose the Design Surface from the dropdown — this lists all DXF files uploaded to the current site.
5. Choose the Layer from the dropdown — only layers containing line or mixed features are shown.
6. Click Import to create the alignment.

SiteView reads the polyline vertices from the selected layer, computes the total length and segment bearings, and creates an alignment record with straight-line horizontal elements connecting each pair of adjacent vertices.

How the Conversion Works

When you select a DXF layer, SiteView performs the following steps:

1. Extracts vertices — reads all vertex coordinates from the polyline features on the selected layer.
2. Computes segments — calculates the distance and bearing between each pair of consecutive vertices.
3. Assigns chainages — the first vertex starts at chainage 0+000 and each subsequent vertex is assigned a chainage based on the cumulative distance along the polyline.
4. Creates horizontal elements — each segment between two vertices becomes a line element in the horizontal alignment with a start point, end point, and computed length.
5. Stores the alignment — the alignment is saved with the simplified: true flag and a reference to the source DXF layer name.

The result is a valid alignment that supports all of SiteView's alignment features — chainage markers, cross-sections, and conformance checking — but with straight-segment geometry only.

💡 Tip

If your DXF polyline has many closely spaced vertices along curves (for example, a polyline generated by exploding a spline in AutoCAD), the straight-segment approximation will be quite accurate. The more vertices along a curve, the closer the polyline follows the true arc.

Limitations

DXF layer alignments have several important limitations compared to LandXML imports:

No Curve Metadata

DXF polylines do not carry curve radius, spiral, or rotation information. Each segment is a straight line between two vertices. This means:

• Bearings change abruptly at vertices rather than transitioning smoothly through spirals.
• Cross-section orientation at vertices may not perfectly match the true design tangent direction.
• Chainage calculations are based on chord lengths rather than arc lengths, so there may be small discrepancies compared to the design chainage.

No Vertical Profile

DXF layer alignments do not include vertical geometry (grades and parabolic curves). If your DXF polyline vertices have Z values, SiteView uses those for the elevation at each vertex, but it does not interpolate a vertical profile between them. Design elevation at intermediate chainages is linearly interpolated between the nearest vertices.

Segment Approximation

On tight curves, the straight-segment approximation deviates from the true curve path. The deviation depends on the curve radius and the vertex spacing. For a 200-metre radius curve with vertices every 10 metres, the maximum deviation from the true arc is approximately 60 millimetres — acceptable for many construction QA purposes but not for precision setting-out.

Coordinate System Handling

SiteView uses the coordinate system that was detected when the DXF design surface was originally uploaded. The same coordinate system (MGA2020, NZTM2000, or WGS84) is applied to the alignment vertices when converting to WGS84 for display on the CesiumJS globe.

If the coordinate system was not correctly detected during the DXF upload, the alignment will be positioned incorrectly on the map. In this case, re-upload the DXF with the correct coordinate system setting.

⚠️ Watch out!

Ensure your DXF design surface has the correct coordinate system before creating an alignment from it. The alignment inherits the coordinate system from the parent design surface and cannot be changed after creation. If the alignment appears in the wrong location on the globe, delete it, correct the design surface coordinate system, and re-create the alignment.

DXF vs LandXML: Choosing the Right Approach

💡 Tip

You can always replace a DXF layer alignment with a LandXML import later. Delete the simplified alignment and import the LandXML file when it becomes available. Your cross-section and conformance results will be more accurate with the full geometry.

What's Next?

• Learn about chainage markers displayed along the alignment on the map
• Generate cross-sections at specific chainages to compare survey and design
• Run conformance checks to verify as-built accuracy
• For full-precision alignments, see LandXML Import