Logging: Printing, Export and Statistics

Getting a log out of VRGS: on paper, as an image, as numbers and as files. Digitising a log and editing its beds is in Geological Logging.

Printing

File > Print (or Ctrl+P) in a 2D log view asks for a vertical scale, such as 1:50, or 0 to fit the panel on one page. It then opens the print dialog. The panel is printed at that scale on as many pages as it needs, across and down. Choose Microsoft Print to PDF as the printer to make a PDF. The background, the cursor readout and the editing handles are not printed. Print preview is not available for the 2D log view.

• Title block. Each page ends with a title block: the panel's and the project's names; the logs; the vertical scale with a bar a metre of log long; the thickness (TVT, TST or MT); how the depth axis reads; the date; and the page number.
• Headers on every page. On a page after the first, the track headers and log names are drawn again at the top of the page, as on a plotted log. If they would take more than half the page, they are not repeated.
• Each page draws only its own part of the panel, so nothing runs into the margins or the title block.
• Orientation. The page orientation chosen in the print dialog is used. A landscape page used to be laid out as a portrait one.

At 1:N only the depths follow the scale. The tracks, the text and the symbols print at their own sizes, as a log is plotted: a track 50 units wide is 50 mm wide on paper at 1:20 and at 1:500 alike. At 0, the whole panel is shrunk or enlarged to fit the page.

Fill patterns are drawn the right way up on screen and in print, as they always were in the SVG export.

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Exporting at scale

Right-click the panel's background:

• Export to SVG asks for a vertical scale, such as 1:50, or 0 to keep the screen's. The SVG is drawn a millimetre to a world unit. At 1:N the depths follow the scale, and the tracks, text and symbols keep their sizes, as in print. The title block goes under the panel.
• Export to PNG... asks for the vertical scale and then the resolution in dots per inch (300 by default, 30 to 2400). The image is drawn in the same way as the SVG, with the title block under the panel, and it records its resolution. It can be up to 32,000 pixels on a side. For a longer log, use a smaller scale or a lower resolution: at 1:50 and 300 dpi that is about 125 m of log.
• Export to PDF... asks the same scale and resolution and writes a PDF of one page the panel's own size, so a metre of log on paper is the scale's metre in any PDF viewer, with the title block and legend. The page holds the panel as a picture at the resolution you chose; for a vector drawing to edit, use the SVG.

Where names would print over each other, such as interpretation crossings close together or notes on neighbouring annotations, the first is written and the rest are left out. The lines and symbols are all drawn, and the names come back as the vertical scale opens the log out.

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Statistics report

Statistics Report... writes a log's statistics as a web page, with its charts drawn in it, and writes the beds behind them as a CSV. Open it from:

• the background of a 2D log view (right-click), for every log in the panel;
• a log's header in a 2D log view, for that log;
• Analysis → Statistics Report... on a log in the Data tree.

It first asks when a bed counts as net: pick one of the project's grain-size classes, and a bed is net when the coarser of its base and top grain sizes is that class or coarser. No net to gross leaves net to gross out. The class you pick is offered first next time. Then choose where to save the page. The CSV is saved beside it, with _beds.csv in place of the page's extension, and the page opens in your browser.

Thicknesses are true stratigraphic (TST). A covered bed counts in the log's thickness, but not in the facies' shares, the histogram or net to gross. For each log the page has:

• Summary. The exposed and covered beds, the thickness in TVT, TST and MT, and net to gross: the net and gross thickness and the number of beds of each.
• Facies. For each facies: its beds, their thickness and its share of the log, the mean bed thickness, and the geometric mean and the standard deviation of ln thickness, the two figures of a log-normal fit.
• Bed thickness. A histogram whose bins double in width (0.25-0.5 m, 0.5-1 m, and so on), so a log-normal spread of bed thickness looks like a bell. The line is the number of beds the log-normal fit expects in each bin.
• Facies transitions. The embedded Markov chain of the facies, base up: how often each facies is followed by each other one. A run of beds of one facies counts once, and a covered bed, or a bed with no facies, breaks the chain. Each cell gives the count, and in brackets the count a random order would give (Powers and Easterling, 1982). Green cells hold at least one more than random, red cells at least one fewer. Under the table, a chi-square test says whether the order is more than chance, and the transitions seen most often over random are listed as Preferred. The test needs at least three facies.
• Palaeocurrents. A rose diagram of the beds' palaeocurrents in 15° sectors, with each wedge's area in proportion to its count; the caption under it gives the count in the longest wedge. The red line points along the mean direction, and its length is the mean resultant length R: the whole radius when every reading points one way. The Rayleigh test says whether the readings have a preferred direction or cannot be told from a uniform spread. The circular standard deviation is given as well.
• Intervals. Each interval on the log, nested ones indented under their parents, with its rank, beds, thickness, net to gross, main facies and mean palaeocurrent.
• Facies associations. Each association's beds, thickness and share.

A p below 0.05 is read as more than chance. With few beds or readings, a test can miss a real pattern, so read a high p as "not shown" rather than "random".

The CSV has a row for each bed, every log's from its base up: the log, the bed's number, its facies, association and intervals (outermost first, as Formation > Member), its grain size (the coarser of base and top), its TVT and TST, whether it is covered and whether it is net, and the number and mean direction of its palaeocurrents.

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Bed tables and LAS

A bed table has one row per bed, from the base up. Each row holds the bed's base and top (x, y, z), its thicknesses, facies, name, grain size at the base and top, dip and azimuth, base contact, lithologies with their shares, structures, fossils, comment and interval. It also holds the bed's bioturbation index, whether it is covered, its base contact's certainty and its Munsell colour. It is UTF-8 CSV that a spreadsheet opens directly. Lists go in one field separated by ;. A lithology's share follows its name after :, and so does a fossil's abundance (Bivalves:Common).

Correct a table in a spreadsheet and bring it back with Data > Import (the log import) and VRGS bed table (*.csv). That makes a new log from it:

• Columns are found by name, in any order.
• A table listed from the top down is turned over.
• A facies the project lacks is added to it.
• Other names the project's lists do not have are left out, and the messages panel lists them.
• Each bed's grain size runs from its grain_size_base at the base to its grain_size_top at the top. Earlier versions read every bed upside down, so a fining-up bed came back coarsening up.
• A gap between one bed's top and the next bed's base (more than 1 cm) goes in as a covered bed, an interval nobody logged. Earlier versions stretched the next bed down to close it. A bed that starts below the top of the bed under it, or a bed with no thickness, is reported in the messages panel. A bed with no thickness is left out.

The LAS 2.0 export asks which thickness its depths follow: TVT, TST or MT (along the log's path). LAS is a well format, so its depth (DEPT) runs down from the log's top. An outcrop log is measured up from its base, so each row also carries HGT, the height above the base in the same thickness: HGT = total thickness - DEPT, and the file's ~Other section gives the total.

The log is sampled every 5 cm. At each depth the file records:

• the elevation on the log's path;
• the grain size in mm and phi from the bed's profile;
• the facies code and the bed number;
• when an image extracted along the log has an outcrop profile, the outcrop's STAND (standout, m), BRIGHT (brightness, 0 to 1) and FACE (the face's angle from horizontal).

~Other names the facies codes.

SedLog

SedLog is the free graphic-log program many sedimentologists and students draw their logs in. Its CSV is how logs usually move between programs.

• Import: choose Data > Import (the log import), then SedLog (*.csv). Each file becomes a log, a straight column from the project's origin, one bed a row from the base up. Its columns are found by name: THICKNESS (CM) (or THICKNESS (M)), BASE BOUNDARY, LITHOLOGY and LITHOLOGY % (and further numbered pairs), GRAIN SIZE BASE, GRAIN SIZE TOP, SYMBOLS IN BED and NOTES. A bed's first lithology is also its facies, and a facies the project lacks is added to its list, as the bed-table import does.
• Grain sizes: SedLog's sizes (clay, silt, vf, f, m, c, vc, granule, pebble, cobble, boulder, or a range such as clay/silt) become the project's grain-size classes. A class named for one (Medium Sand, Clay) takes it; otherwise the class whose range holds the size does.
• Base boundaries: Sharp, Erosion and Gradational become the Sharp, Erosive and Gradational base contacts.
• Symbols: a symbol naming a bioturbation level, such as Intense bioturbation, sets the bed's bioturbation index. Any other symbol becomes a fossil when the project's Palaeontology list has it, and a structure otherwise.
• The messages panel lists any column the reader does not know, and any name the project's lists do not have.
• Export: right-click a log in the Data tree, choose Export, then SedLog (*.csv). It writes SedLog's seven published columns. Each bed's thickness is in centimetres of TST, and its grain sizes are in SedLog's names. Only the first lithology and one symbol go out per bed, since SedLog reads one of each per row.

StraboSpot measured sections

A StraboSpot import (StraboSpot Login on the Edit tab) also brings in measured sections drawn in StraboField's Strat Mode. Each section becomes a log, named after the section, rising from the section's spot. Its intervals become beds from the base up, carrying their:

• thickness (in cm, m, in or ft);
• lithology, as the bed's facies;
• grain size, as the project's class;
• physical structures;
• bioturbation index;
• fossils.

An unexposed or unmeasured interval becomes a covered bed. Notes, colours and the interval's weathering resistance go into the bed's comment. A section whose log the project already has, by name, is not imported again. The import summary counts the sections imported.

LAS curves onto a log

Import > Geophysical Log Tracks... on a log's menu in the Data tree, with LAS Well Log, puts a file's curves on that log. On a log with beds it asks which way the file's index runs:

Choice	For
Depth down the log's path from its top (MT), as a well's	Wireline files. As before, the file's KB elevation places it when it can.
Depth below the log's top, TVT or TST	A file written top-down in one of the log's thicknesses, such as VRGS's own export.
Height above the log's base, TVT, TST or MT	Field logs measured up a section, such as a gamma-ray log taken every 25 cm from the base.

The list starts on what the file's index is called: HGT or HEIGHT suggests a height above the base, and DEPT a depth. Each row is placed on the bed at its height, so a curve stays against its beds in every depth mode. Rows beyond the log's beds are left out, and the messages panel says how many.