Survey and points

This chapter covers the survey side of Terrace: COGO points, point groups, description keys, point files, total-station raw files, traverse and least squares adjustment, and the project's coordinate system. When you finish it you'll be able to bring a field survey into a project, check and adjust it, and sort its points so the surfaces and designs that follow are built from the right shots.

The Survey tab

Everything in this chapter starts from the Survey ribbon tab, the first tab of the window. Its groups follow the order of the work:

Project Settings and Design Standards in the same group open their dialogs; they are covered in Projects and files and Standards and styles. All the commands are also listed in the command reference.

COGO points

A COGO point (coordinate geometry point) is one surveyed position: a point number, a northing, an easting, an elevation (or none) and a description. Every surface, profile and stakeout in Terrace starts from them. Northing is the drawing's Y and easting its X.

Each point keeps two descriptions. The raw description is the code as the field crew typed it (TREE 0.3 MANGO). The full description is what the description keys make of it (Tree 0.3 m MANGO). Labels show the full description; point groups can match either.

In the sample project the 2,134 points are numbered from 1: control first (BLLM No. 1, BM-1, BM-2), then the ground shots (NGL), the creek bed (CRK) and the trees. Point markers go on layer V-NODE and their labels on V-NODE-TEXT, unless a description key names another layer.

Creating points by clicking

Use this to add a few points where you can see them: a spot you need on the plan, a missing shot, a point read off a sketch.

1. Click Survey ▸ Create Points (or type CREATEPOINTS, alias CPOINTS). The command line says the next free point number.
2. At Specify point location or [Typed/Number], click the location.
3. At Elevation [None/Surface], press Enter to take the default. When there's a ground surface under the point, the default is its elevation there; otherwise it's the last elevation you typed. Type a number to give another, N for no elevation, or S for the surface's.
4. At Description, type the code (for example NGL) or press Enter to repeat the last one.
5. Click the next location, or press Enter to finish.

Each point is reported on the command line as it is made. All the points of one run are one undo step, and surfaces built from them are brought up to date once when the command ends, so even a long run stays quick.

To start numbering somewhere else, type N (Number) at the location prompt and give the next point number. Numbers already used are skipped.

Typing coordinates

Use this to key in points from a field book or a list of control coordinates.

1. Start CREATEPOINTS and type T (Typed) at the first prompt.
2. At Enter northing,easting,elevation[,description], type a line the way surveyors write it: northing first. For example 1610195.500,522648.200,58.080,TREE 0.3 MANGO. Spaces between the numbers work too; the elevation and description can be left off.
3. Press Enter and type the next line. Press Enter on an empty line to finish.

A line without a description takes the last one you used.

Moving, copying and deleting points

Points are edited like any other civil object (see Selecting and editing):

• Move: click a point and drag its grip, or use MOVE. Its northing and easting change; its number, elevation and description stay.
• Copy: COPY makes new points with the next free numbers.
• Delete: ERASE. Terrace says what depended on them before it removes them.
• Locked points (some imports lock control points) refuse to move.

Selecting points shows a summary in the Properties panel: how many points the project has, how many have an elevation, the elevation range, the number of point groups and description keys. A point's own elevation and description can't be typed over in the panel; to change them, import the point again with Replace the old (see Importing a point file).

Point groups

A point group is a named set of points chosen by rules: by number, by code, by elevation. Surfaces are built from groups, so groups decide which shots go into the ground model. A group keeps itself up to date: a new NGL point joins a group that takes NGL* without you doing anything.

The sample project has three: All Points, Topo (codes NGL*,CRK*: the ground and creek shots the EG surface is built from) and Control (BLLM*,BM*).

Making a group

Make a group when you want a surface, a report or an export to use only some of the points: the ground shots, the trees, one day's work.

1. Click Survey ▸ Point Group. The New Point Group dialog opens with a free name filled in (Group 1 in a project that has none).
2. Type a Name and, if you like, a Description.
3. Say which points belong to it. Tick Every point in the project for all of them (the other rules then hide), or fill in one or more of:
   • Point numbers: ranges like 1-50, 75;
   • Codes: field codes like GND*, TOE, EP* (* matches anything, ? one character; capitals don't matter);
   • Elevations: ranges like 90-120, or a single elevation.
4. Put numbers to keep out in Leave out numbers (for example a bad shot).
5. Watch the line under the fields: It holds … of the project's … points now counts the members as you type. Click Create.

The group appears in the Project browser under Points & Groups, and the command line says how many points it holds. It's one undo step. A name already used is refused, and so is an empty one.

Or type POINTGROUP (alias PGROUP) to make the group on the command line:

1. At Point group name [Dialog], type a name or press Enter for the suggested one. Type D (Dialog) here to open the New Point Group dialog instead.
2. At Include points by [All/Numbers/Descriptions/Elevations], choose one:
   • A (or Enter): every point in the project;
   • N: point numbers as ranges, like 1-100,205;
   • D: descriptions, like EP*,CL*;
   • E: an elevation range, like 100-150.
3. Type the numbers, codes or range. Terrace says how many points the group holds.

Changing a group's rules

Click a group in the Project browser: its rules show in Properties, and you can change any of them. Every change is one undo step, and every surface built from the group rebuilds by itself.

A point belongs to the group when it matches any include rule and no exclude rule. A group with no include rule at all is empty.

The Report… button opens the point group report: every member with its northing, easting, elevation and descriptions (see Survey reports).

Description keys

Field crews type short codes: NGL, CRK, TREE 0.3 MANGO. Description keys turn each code into a readable description and put the point on the right layer, so the plan reads well and you can turn whole classes of points on and off by layer.

1. Click Survey ▸ Description Keys (or type DESCKEYS, alias DKEYS).
2. Edit the table: double-click a cell to change it. Add key adds a row; select rows and click Delete keys to remove them.
3. Leave Apply to the points already in the project ticked to redo the descriptions of the points you have, then click OK.

A point whose code matches no key keeps its raw description as its full description. Keys apply to every point you add from then on: typed, clicked or imported.

Importing a point file

Most surveys reach the office as a text file of points: one point per line, with number, northing, easting, elevation and description in some order. The Import Points dialog reads them with a preview, so you can see the columns are right before anything is added.

1. Click Survey ▸ Import Points (or type IMPORTPOINTS, alias POINTSIN) and choose the file (.csv, .txt, .pnt, .nez, .xyz). You can also drop the file on the window (see Drag and drop).
2. Read the line under the title: how many lines the file has, and the column order and separator Terrace found.
3. Check the preview table: its columns are Point, Northing, Easting, Elevation and Description, read the way the settings say. If the northings sit under Easting, change Columns; the preview follows at once.
4. Choose what to do with numbers already in the project, and whether to make a point group and a surface.
5. Click Import.

A file without point numbers (NEZ, ENZ …) gets numbers from the next free one; the preview shows them as “(next)”. The import is one undo step, and the command line says how many points came in, how many were replaced or skipped, and the group and surface made.

Total-station raw files

A raw file holds what the total station measured, not coordinates: for each setup (the instrument over a known point, sighting a backsight), the horizontal angle, zenith angle and slope distance to every shot, with instrument and target heights. Terrace reads the observations and reduces them: it computes each shot's coordinates from the station and backsight. Keeping the observations lets you adjust the traverse and the network afterwards.

1. Put the control in first: the station and backsight points need coordinates. Import or type them (they may also be in the raw file itself: RW5 SP records and similar are read as known points).
2. Click Survey ▸ Import Raw File (or type IMPORTRAW, alias RAWIN) and choose the file.
3. Check the File format (picked from the extension; choose another and click Read again if it's wrong) and the summary line: setups, observations and points with known coordinates.
4. Look over the observations in the table: Station, Backsight, Point, Horizontal, Zenith, Slope dist., Target ht., Description.
5. Choose Point numbers already used: Keep the project's (default) or Replace with the file's, and whether to Put the points in a point group (named after the file). Click Import.

What reduction does for you:

• Setups are reduced in file order; a setup's station must be known by then (from control, or from an earlier setup's shot).
• Horizontal distances are multiplied by the project's combined factor, so ground distances become grid distances.
• Elevations come by trigonometric levelling, with instrument and target heights.
• Shots to a backsight, to control points, to locked points, and repeated shots are checks: they move nothing, and a note says so when one misses by more than 0.01 m.
• Point names that aren't numbers (like CP1) get numbers after the highest one in the file, and a note tells you which.

The setups and observations stay in the project for TRAVERSE and LEASTSQUARES. Importing again adds the new setups to them.

Traverse adjustment

A traverse is a chain of setups, each one sighting back to the last and ahead to the next. Measurement errors add up around it, so a closed loop never quite closes. The misclosure is how far it misses; the precision is the length of the traverse divided by that miss (1:20,000 means 1 cm in 200 m). Adjusting spreads the miss back over the stations so the traverse closes.

1. Import the raw file (above). TRAVERSE needs observations; without them it says “import a raw file first”.
2. Click Survey ▸ Traverse (or type TRAVERSE, alias TRAV).
3. At Stations in order, press Enter to take the suggestion (the setups' stations in order, the first repeated to close a loop: 1001,1002,1003,1004,1001) or type your own. At least three stations.
4. At Backsight point at the first station (0 = none), press Enter for the first setup's backsight.
5. At Adjust by [Compass/Transit/CRandall/Least squares], choose the rule (Enter for the last one used; Compass the first time).

The angular misclosure is first balanced equally over the angles; elevation misclosure is spread by distance. The adjusted points move, as one undo step, and the command line lists every course (from, to, direction, distance, the latitude and departure corrections, adjusted northing and easting), then the misclosure and the precision:

The traverse is kept by name (Traverse 1, Traverse 2 …). Run TRAVERSE again to re-adjust it with another rule: it lists the traverses and asks Traverse name or [New]; Enter takes the first one, N defines a new one.

The Traverse adjustment report shows the adjusted coordinates with the method, misclosures and the course table, ready to save as CSV or PDF:

Least squares network adjustment

When a survey has more measurements than it strictly needs — shots to the same point from two setups, ties between traverses, check shots — least squares uses all of them at once. It finds the coordinates that make the sum of the weighted squared residuals smallest, and tells you how good each point is.

1. Import the raw files of the network.
2. Click Survey ▸ Least Squares (or type LEASTSQUARES, alias LSQ).
3. At Control points to hold fixed (numbers or ranges), press Enter for the default (the first setup's station and backsight: 1001,1009) or type your control points. Hold at least one point, and two to fix the orientation when there's no backsight azimuth.

The command line shows the report (up to 60 lines) and moves the adjusted points, as one undo step. What it says:

The instrument accuracy assumed by default: distances 3 mm + 2 ppm, angles 5″, centering and target 2 mm.

Coordinate systems

Philippine surveys are tied to PRS92, the Philippine Reference System of 1992: a Transverse Mercator grid in five zones, 2° wide. Older plans use Luzon 1911 on the same zones. Setting the project's system lets Terrace exchange data with GIS files and Google Earth, and work out the combined factor. New projects start with none (plain local coordinates); the sample project is in PRS92 zone 3 (EPSG:3123).

1. Click Survey ▸ Coordinate System (or type COORDINATESYSTEM, alias CRS or EPSG). The command line shows the current system.
2. At EPSG code or [List/None], type the code (the default is the current one, or 3123), L to list every system Terrace knows, or N to go back to local coordinates (factor 1).
3. At Combined factor (grid × elevation) or [Compute], type the factor, press Enter to keep the current one, or C to compute it.

The combined factor

A distance measured on the ground isn't the same length on the grid. The grid scale factor (from the projection, about 0.99995 near a PRS92 central meridian) and the elevation factor (the ground is above the ellipsoid) together make the combined factor: grid distance = ground distance × combined factor. Terrace applies it when reducing raw observations.

C (Compute) works it out at the center of the project's points and their mean elevation:

A factor must be between 0.9 and 1.1 (real ones are 0.9996 to 1.0004). For a longitude/latitude system the factor is 1. The coordinate system and factor are also in Project Settings (see Projects and files). The change is one undo step.

Exporting points

Send points to a data collector for stakeout, or to another program.

1. Click Survey ▸ Export Points (or type EXPORTPOINTS, alias POINTSOUT).
2. At Point file to write, type the file name (for example survey-points.csv).
3. At Column order [PNEZD/PENZD/PNEZ/PENZ/NEZ/ENZ], pick the order or press Enter for PNEZD.

The file is comma-separated with four decimals, and holds every point of the project with its full description. To send only some points, use the Point list report's Save CSV… (below), or export LandXML or GIS data (see Importing and exporting).

Survey reports

Type REPORT (or click Report… on a point group in Properties) and pick one under Survey. Each shows a live preview and saves as CSV or PDF; see Reports for the dialog.