Point Groups and Surfaces

Point Groups and Surfaces

A point group is a named rule that selects survey points. A surface is a TIN triangulated from one or more point groups. Groups feed surfaces, so build them in that order.

Point Groups

Ribbon: Survey → Groups

A group stores a rule, never a member list. Membership is recomputed from the current points every time it is asked for — so a point imported after the group was defined joins it with no edit, and a deleted point leaves nothing behind.

Creating a group

Press New point group. Give it a name — names are unique within the drawing, and an empty name is refused ("Point group name cannot be empty…", "A point group named … already exists — rename refused.").

The rule

Include points matching ANY of:

The criteria combine as a union (OR). A point joins the group if it matches any filled-in criterion.

Wildcards are case-insensitive: * matches any run of characters including none, ? matches exactly one, everything else is literal. Case-insensitivity is deliberate — field codes are typed in the field, and eg meaning something different from EG would be a trap.

A group keyed on Raw description matches = EG, so office edits to the description cannot break it.

An empty rule matches nothing, not every point. The dialog says so: "No criteria set — this group contains 0 points." Treating "no filter" as "match everything" is how a whole drawing ends up in a surface by accident.

Working with a group

Description versus raw description

This is the reason both fields exist.

A crew codes a point EG. The office expands the description to EXISTING GROUND — SW CORNER. A group keyed on description stops matching. A group keyed on raw description keeps matching, because the raw code is never rewritten by an edit to the description.

Key surface-building groups on raw description.

Points saved before raw descriptions existed have an empty raw field; those fall back to the description rather than being skipped.

Surfaces

Ribbon: Survey → Surfaces

A surface is built from point groups — create one in Survey ▸ Groups first.

A surface is a TIN — a triangulation of the points in the groups you choose.

Creating a surface

1. Open Surfaces and press New from group…
2. Name the surface. Names are unique; an empty name is refused.
3. Under Build from point groups:, tick the groups to include. The dialog reports the total — N point(s) selected.
4. Press Create.

At least three points are required. With fewer, the dialog says N point(s) selected — need at least 3. and Create is unavailable.

A surface built from the Existing Ground group — 500 points, 982 triangles, elevation 103.52 to 136.62 — with the TIN drawn behind it.

The surface list

Rebuilding

Rebuild re-triangulates from the current points in the listed groups.

Rebuilds from the current points in the groups above.

Because groups are rules, importing more points that match a group and then pressing Rebuild is all it takes to bring a surface up to date. Nothing needs re-selecting.

Renaming and deleting

Rename surface and Delete surface are on the right of the panel. Both are confirmed in the command log.

Displaying a surface

A surface is drawn as its triangle edges — a wireframe mesh over the points.

Visual style does not shade a TIN. Setting Visual style to SHADED has no effect on surfaces: they render as triangle edges in all three styles. SHADED fills imported meshes (IMPORTMODEL) and hatches, not TIN surfaces. Lit surfaces are a planned feature, not a current one — see Known Limitations.

To read a surface in three dimensions, orbit it. Type ORBIT (3DO) and drag: the elevation differences become obvious as the mesh tilts, which is the check that catches a bad shot or a spike in the triangulation. SURFELEV gives you the numbers.

The same surface after ORBIT. The ViewCube (top right) shows the view is no longer plan. This is a wireframe of triangle edges — no visual style fills it.

See Views and Navigation.

Reading elevations off a surface — SURFELEV (SE)

Ribbon: Inquiry → Elev/Grade Command: SURFELEV, SE

SURFELEV — pick a point for its surface elevation; pick a second for grade. ESC cancels.
SURFELEV: Pick a point for its surface elevation | ESC cancel
SURFELEV: Second point for grade | ESC stops after the elevation

• First pick — reports the interpolated elevation on every surface covering that point.
• Second pick — reports the grade, slope, and distances between the two.

A pick that falls outside a surface says so rather than extrapolating a number you should not trust.

With no surfaces in the drawing the command refuses to start: SURFELEV — there are no surfaces in the drawing. Build one from a point group first.

A worked example

Goal: a ground surface from field shots, excluding the control points.

1. Survey → Groups → New point group. Name it EG.
2. Set Raw description matches to EG*. The dialog reports how many points match.
3. Survey → Surfaces → New from group… Name it Existing Ground.
4. Tick the EG group and press Create. The panel reports the point and triangle counts and the elevation range.
5. Type ORBIT and drag to tilt the view — a 3/4 angle exposes spikes and bad shots that a plan view hides.
6. Use SURFELEV to spot-check elevations against known shots.

Later, after importing a second day of shots coded EG:

7. Survey → Surfaces, select Existing Ground, press Rebuild. The new points are already in the group.

Common problems

Related

Survey Points · Views and Navigation · Inquiry Commands · Traverse Editor