Field Recording

Equipment Needed

The following list should be considered the minimum equipment required to record rock art using the DigitalRockArt system.

• Digital camera with extra media storage and batteries
• Compass - Silva Ranger Compass Type 15 or comparable with clinometer (or a regular compass and a separate clinometer)
• A metric electronic measuring device with extra batteries or a 30 to 50 meter measuring tape
• A short steel metric tape for measuring panel width and height
• Plastic sandwich bags with cluster numbers for markers
• Light reflector/shade screen
• Clip board, pencils and eraser
• DRA recording forms
• GPS meter

In addition to the above, some recorders may prefer to carry these additional items. For camping trips lasting several days in remote areas, the use of a laptop computer will be required for downloading the camera media chips and sorting the images in the field.

• Tripod
• Filters
• Laptop computer
• Color keys

The use of mug boards, north-pointing arrows and metric scales are not recommended because these consume setup time and only add redundant information. The DigitalRockArt application has better methods of creating image captions with relevant data.

Locate and Tag Clusters

The most efficient approach to the field survey work is to split the recording team into two work units; one unit will do the photography and the other the ground survey. A team of three is the optimal size with one person doing the photography and two people doing the ground survey. Alternatively, the survey can be done with just two people or use a fourth person to work with the photographer.

After arriving at the site, the first step is to decide where to start. If the site is too big for one day's work, it is best to pick some natural boundary and concentrate on doing a portion of the site. Once the area to be recorded that day is determined, the photographer can begin to locate and photograph any panels that will benefit from the current lighting conditions.

The ground survey unit will choose a dominant or outstanding cluster or other some other permanent feature as a starting datum point. Starting with the chosen datum point, the area is thoroughly searched. Pre-numbered bag markers are placed on or near the clusters to be recorded. The markers should be placed in an orderly sequence to facilitate recording. A few pebbles or sand may be added to the bags to prevent them from being blown away by wind gusts. If you later find another cluster you missed as you are surveying, you will place a surplus marker near it and include it in the survey.

Grinding slicks, metates, tool marks, historic writing, and vandalism are always recorded in the same manner as primitive rock art and require markers to indicate their locations. Samples of pottery sherds, lithics, structures, and historic artifacts can be photographed as well but these do not require markers because they will not be measured nor included on topography charts.

Completing the Recording Form

Overview - It is advantageous to do the ground survey in two passes: pass one for "Panel Measurements" and sketches, pass two for "Datum to Panel Measurements". The first pass may be completed by one or two people, the second pass requires two people. To start, enter the date, recorder names and site name or number at the top of the form.

Starting with the first cluster, determine the number of panels and identify the boundaries that separate the panels. For boulder clusters with multiple panels, make the dominant panel "A" and letter the other panels in a counter-clock wise direction around the boulder and the top last (unless the top is the dominant panel). For cliff face clusters with multiple panels, make the dominant panel "A" and letter the other panels left to right and top to bottom. Lettering panels in this manner will achieve good results later when multiple images are displayed on a page left to right and top to bottom in cluster-panel sequence.

Sketch each panel while standing in the approximate position the photographer will use to photograph the panel. For complex panels, it is not necessary to draw all the elements. The sketch should include the cluster number and panel letter, outline of the panel, unique or dominant elements, natural blemishes or cracks in the rock, the position of adjacent panels, vegetation, etc. Finally, determine where the panel width and height will be measured and mark the measuring end points on the sketch.

There are two schools of thought on measuring the width and height of panels. One way measures the decorated area of the panel, the other way measures the available area. Measuring the available area is preferred because sometimes digital images taken at different times of the day will reveal elements that are invisible at the time the measurements are made. Choose end points for measurements that will be easy to identify on the sketch and locate later on the digital images. Good choices include the widest or highest distances, cracks and odd bumps on the panel edges. Measurements need not be exactly horizontal, nor vertical, nor perpendicular to each other.

Panels larger than about 1.5 meters must be photographed in sections in order to obtain sufficient resolution to show each cropped element in detail. When possible, avoid this problem by using small cracks or variations in the rock to define several smaller panels. An alternative is to consult with the photographer on how to shoot the panel in sections, and then use the form comment or sketch area to notate the measurement of an element within each section. The reason for doing the additional measurements is to provide a relative scale for each digital image later on in the Categorize Images function.

Continue the panel measurements so the recording form is filled out in cluster-panel sequence. As the forms are filled with Panel Measurements, share them with the photographer and resolve any disagreements related to the number of panels on each cluster, panel boundaries and panel facings. After all the panel measurements have been completed and reviewed with the photographer, collect the forms so the "Datum to Panel Measurements" can be completed.

Large sites will require secondary datum points so the topo charts generated by the DigitalRockArt application can be split into multiple pages. A guideline is to keep most distances between datums and panels to 10 meters or less. This implies that the distances between datums and secondary datums should be about 20 meters. Choose datums that are easy to see and easy to access. Distance, bearing and elevation measurements are always taken from the datum point to the "A" panel of the target cluster. For this operation, two people are required. One stands at a datum and the other moves from cluster to cluster assisting in the measurements.

For most surveys, distance, bearing and elevation measurements are only taken for "A" panels. The DigitalRockart system does not collect any data related to the size of the boulder or gallery that makes up a panel cluster. If there is a desire for more detailed information and sufficient work hours are available in the field, then the distance, bearing, and elevation measurements for the "B", "C", "D",... panels can be taken by using the cluster's "A" panel as a datum point. In many cases this will present the challenge of estimating a measurement that must be made through solid rock. Collecting this data creates many more points to be plotted on the topo charts. To maintain readable charts, the distances between primary and secondary datums should be reduced to about 15 meters instead of 20 meters. As shown below, any information that is perceived to have been lost because the boulder size was not recorded can be more than compensated for by plotting the relative position and facing of the panels on a 1-meter grid.

Using a Compass

Before taking measurements, the compass must be adjusted for the local magnetic declination. The earth's magnetic north is located in Hudson Bay in Canada, not the North Pole. The magnetic declination varies depending upon your location. In Arizona it varies from about 12 to 14 degrees east. The usual way of determining the correct declination is to consult a topo map.

To adjust your compass for declination, open the mirror lid flat and hold it in a horizontal position with the bottom (lanyard) closest to your body. Rotate the compass dial until 360 degrees or the cardinal point "N" is under the index pointer. On the lanyard there is a metal screwdriver attached and a declination adjusting screw embedded in the top (or bottom) of the rotating dial. Turn the screw so the orienting arrow coincides with the magnetic declination for your location on the declination scale.

Before taking any measurements in the field using the compass, be aware of potential magnetic interference from the local rocks, a steel measuring tape, belt buckles, power lines or other sources. If possible, it is a good idea to stand away from any potential sources of magnetic interference and make a mental note of a landmark on the horizon close to magnetic North (or South) before beginning to measure a site. Then as each measurement is taken, do a quick check to insure that there is no magnetic interference by verifying the needle is pointing in the expected direction.

Measuring Distance - One person holds the display end of the electronic measuring meter or the reel end of the measuring tape. The second person holds the target device or end of the tape. The distance in meters is measured from the center of the datum to the center of the target panel.

Measuring Bearing - The bearing is the direction or degree reading from 1 to 360 degrees from the datum to the target panel being surveyed. There are three methods of using the compass to take a bearing. First, you need to be at a place where you, the datum and the target panel are in direct alignment. If possible, stand behind the datum and sight over it to the target. Otherwise, stand in front of the datum with your back toward the datum.

Hold the compass base in horizontally in front of you at eye level and open and adjust the mirror lid so that you see the dial in the mirror. Sight the target panel using the compass site. Then while using the mirror to view the top of the compass dial, rotate the dial until the magnetic needle and the orienting arrow align. Read the bearing at the index pointer. This is the most accurate method.

If you are measuring the distance between the datum and the target panel with a nonmagnetic tape, an alternative method is to completely open the mirror lid so the compass body is flat. Holding the compass on the stretched measuring tape in one hand with the compass sighting line aligned with the tape, rotate the dial until the magnetic needle and the orienting arrow align. Read the bearing at the index pointer.

A third method is to open the hinge completely, hold the compass body flat at waist level away from your belt buckle, point the top of the compass at the target panel, rotate the dial until the magnetic needle and the orienting arrow align. Read the bearing at the index pointer.

Measuring Elevation Change - Measurement of the elevation change from the datum to the target panel is not a common measurement. If the rock art site being surveyed is a relatively level boulder strewn field, then elevation changes will usually be near zero and the measurement can be omitted. However, when working on sites composed of scree, cliff faces, or caves, the inclusion of an elevation change can be a useful measurement that will aid in finding the panel sometime in the future.

Elevation change measurements can be made using the clinometer feature of a compass. The clinometer feature consists of an arrow on a pendulum that rotates around the dial based upon the pull of gravity. Degree markings inside the dial go from 0 to 90 degrees. Frequently there will be two 90 degree scales inside the dial for ease of use.

Elevation change is a direction or degree reading from -90 to +90 degrees from the datum to the target panel. A horizontal measurement is 0 degrees. If the target panel is directly above the datum, the elevation change is +90 degrees; should the target panel be directly below the datum, the measurement would be -90 degrees. Think of this measurement as being similar to road signs that advise you of 6% downgrades or 7% upgrades on the road ahead.

To use the clinometer, open the mirror lid completely and turn the compass dial so that the 90 degrees or the cardinal point "E" is set at the index pointer. Position yourself between and off to the side of both the datum and target panel. Hold the compass at eye level with arms stretched so that the clinometer needle is hanging vertically and overlays the scale at the bottom of the compass. The cardinal point "S" on the compass should be pointing downward. Let one long side of the compass coincide with the slope of the terrain and read the measurement from the declination scale. Because there are no positive or negative measurements on the clinometer, you will have to remember to add the negative sign on the recording form for all downward measurements.

Measuring Facing - The facing is a direction or degree reading from 1 to 360 degrees. The facing is the direction the panel is "looking". For example, a picture hung on the North wall of a room is facing South, or 180 degrees. To obtain a reading, open the mirror lid completely, stand in front of the panel and hold the top edge of the compass (lanyard toward the panel) perpendicular to the panel as close as possible without getting any magnetic interference. Rotate the compass dial until the magnetic needle and the orienting arrow align. Read the facing degree measurement at the index pointer.

An alternative technique for more experienced users is to stand facing the panel from several feet away. Hold the compass in the normal position with lanyard toward your body, rotate the compass body to coincide with the panel facing, rotate the dial until the arrows overlay, and then take the back bearing degree reading from the bottom of the compass near the lanyard.

If the rock art panel is perfectly horizontal with inclination reading of 0 degrees (like a table top) or 180 degrees (like a ceiling) then the facing should be based upon the direction of the elements, or recorded as 0 degrees if no direction can be determined. If the measured facing is true North, it is recorded as 360 degrees (not 0).

For all panels with an inclination of less than 90 degrees (table top to almost vertical), the facing is the direction of the slope of the panel. For all panels with an inclination of more than 90 degrees (an overhang or cave ceiling), the facing is the opposite direction of the slope. To picture this, draw two rock art elements near the top and bottom of a sheet of paper, fold the paper in half, then open it so the bottom half has an inclination of about 45 degrees and the top half has an inclination of about 135 degrees. The facing of both halves is the same direction.

You may encounter situations where a boulder has shifted or fallen and the present facing of the panel is not of the same orientation as the elements on the panel. In this case, the rule is to measure the facing of the rock rather than the elements, and make a note on the recording form that the panel has shifted. The quick sketch should show the panel elements in their current orientation.

In many cases the panel being measured will have an irregular or rounded shape. In this case, you should try to measure the average facing of the individual elements. If there is one dominant element and several minor elements, an alternative is to measure the dominant element's facing.

Measuring Inclination - The inclination measurement is from 0 to 180 degrees. A horizontal surface similar to a table top is measured as 0 degrees, a vertical wall as 90 degrees, and a horizontal surface such as a ceiling as 180 degrees. There are no negative inclinations nor any inclinations over 180 degrees. This measurement is consistent with the way facing is measured, so that a floor is facing upward or 0 degrees, a vertical wall is facing outward or 90 degrees and a ceiling is facing downward or 180 degrees. But rather than continuing down from the ceiling on the opposite wall to get a reading of 270 degrees, we would start over from the floor with its 0 degree inclination and measure the opposite wall as 90 degrees of inclination.

Measuring inclinations between 0 and 90 degrees is straightforward. Open the mirror lid completely and turn the compass dial so that the 90 degrees or the cardinal point "E" is set at the index pointer. Lay the side of the compass with the cardinal point "S" on the surface to be measured and take the reading from the clinometer.

Measuring inclinations above 90 degrees is more difficult because most clinometers only go up to 90 degrees. The easiest method is to hold the top of the compass against the panel, take the reading and add 90 degrees. For example, if you were measuring a panel with a slight overhang, you would discover that when you hold the long edge of the compass against the panel the pendulum needle of the clinometer will swing past 90 degrees and off of the scale. Rotate the compass to bring the short end against the panel and take a reading, say 20 degrees, and then add 90 degrees. Record the total, 110 degrees, as the panel inclination on the form.

Measuring Width - The width of a panel is measured in meters. Width is a measurement made horizontally across a panel at its widest point. In addition to entering the number on the form, the end points should be marked on the thumbnail sketch.

Measuring Height - The height of a panel is measured in meters. Height is a measurement made perpendicular to the width measurement across a panel at its widest point. In addition to entering the number on the form, the end points should be marked on the thumbnail sketch.

Photography

Equipment Recommendations - It is recommended that a 6 to 12 megapixel digital camera be used for the photography. A digital camera with fewer pixels may not yield cropped elements with sufficient resolution. A larger megapixel size will waste media storage and disk space on your computer and will cause long downloads and backups.

An 8 to 12x optical zoom is useful for shots where it is difficult or impossible to access the best position. Zoom lenses may enable the photographer to reduce the angle of a photograph for a high panel by backing away and zooming in.

A circular polarizer may be useful. Digital cameras employ their own polarizers internally in their light metering and auto focus systems. Putting a simple linear polarizing filter on a digital camera can cause errors in exposure and focus, or disable both automatic metering and focus. For this reason a linear polarizer should not be used. However, you can not see the polarizing effect on digital camera unless an expensive SLR model has been purchased. To compensate, multiple images must be taken where the circular polarizer is rotated an eighth or quarter of a turn.

Enough media storage for 500 JPEG images per day of field recording should be available. A light reflector / shade screen may be helpful in dealing with lighting problems.

Camera Settings - Unless you are an experienced photographer, set the camera in AUTO mode. Auto mode will almost always yield the best results and is much faster.

Use JPEG as the image format at or near the highest quality setting. TIFF images should not be used because they consume too much storage.

Check the camera's setting to insure the date and time are current. If you allow the batteries in your camera to drain, the camera will revert to the manufacturer's default date and time. The date and time from the camera is recorded with each image and will be used later as part of the survey documentation.

Set the camera to continuous file numbering. If continuous file numbering is not set on, every time the media storage is changed, the camera will reset the file number to "one". If you use multiple media storage in one day, when you try to download or copy your images to a folder, it will fail because of "duplicate file name".

Set battery save or auto turnoff on. This will save battery power by putting the camera into a sleep mode if not used for a period of time you chose. Touching the shutter button activates the camera.

Check your camera manual to see whether the camera settings chosen are retained when you turn off the power. The settings may return to original manufacturer's setting you do not set retain settings on.

Your viewfinder should display at minimum the mode, number of storable images remaining and the battery check. Displaying too much information in the viewfinder will obscure your view of the image being taken.

General Rules - Photograph overviews of the site and each cluster and panel multiple times during the day as the lighting conditions change. The images do not need to be taken in order -- they will be sorted and selected for recording purposes later on the computer. Images should not to be artistic. They should document the rock art and must meet the needs of the DRA application.

Lighting - Lighting problems include the facing of the panel, shiny surfaces, partial shading, shaded panel with the background in sunlight, light or nonexistent patina and shallow pecking. There are a number of options which may remedy lighting problems. Photograph at the time of day when the sun is over your shoulder and a bit to the side. Consider photographing when the sun is blocked (behind a cloud, tree, boulder, mountain) or on overcast days. Try using a shading or reflector screen to balance the lighting.

To alter the light reading, change the angle of the lens a few degrees up or down. Backing away from the panel and using the telephoto lens to zoom in also alters the light reading. For horizontal panels, consider photographing the panel upside down and rotate the image on the computer.

Access - Access may also be a problem. The rock art may be on a narrow ledge, over the edge, high on a wall, on a cave ceiling or in vegetation. Perspective transformation is a computer software option which fixes the horizontal or vertical distortion caused by taking an image at an angle. This computer option produces the best results if the shot is taken straight up or straight to the side. Another computer software option is stitching. Here you stand in one place and take overlapping images. Using specialized stitching software, the images are combined seamlessly into one image.

You might consider taking a blind shot where you hold the camera out and without using the viewfinder or LCD the shot is taken. Walking away and zoom in may remedy a poor or tight angle. In all cases, do the best you can.

Shooting Preparations - Remove backpacks, garbage, vegetation, etc. from the immediate area. Avoid photographing your feet, hands, personal shadows, hanging lens caps, etc. Check the cleanliness of your lens regularly, use your lens cap when not using the camera. Shade your lens to keep it out of the sum. Remember you are not looking through the lens with most digital cameras. Avoid background landmarks that may reveal site location.

Use the viewfinder, not the LCD to frame your images. You are more stable with the camera to your face than holding it out in from of you. Using the viewfinder eliminates peripheral distractions (the camera, hands, background) allowing you to concentrate on framing the image.

Hold the camera level, do not distort the position of the panel. Decide if landscape (camera held in normal position) or portrait (camera turned 90 degrees) will give you a better image.

When ready to take the image, stabilize yourself by planting your feet, bring your arms close to your body, take a deep breath (especially if you are using a zoom) and shoot. Take multiple shots. Between shots, take the camera away from your face and reframe the image. Do not be afraid of taking too many shots, it does not cost more and the best shot may be just one more click away.

Image Considerations - Photograph site overviews with cluster number markers to show the location and relationship between clusters. These images will help with the annotation of the site. Take additional overviews without the cluster numbers that will be used for annotation.

Photograph each cluster with the cluster number marker at least once. These will not be used in the final recording but will be helpful in sorting the images (most images should be taken without cluster number markers). Multiple cluster overviews should be taken if there is more than one panel showing the location or relationship between panels.

Photograph each panel individually. Use facing of the panel to determine your best position: the panel width and height measured by the ground survey should be reflected as horizontal and vertical measurements in your photograph. With your lens perpendicular to the panel, center the panel in your viewfinder capturing the outline of the entire panel. For large panels, take additional overlapping close-ups left to right, top to bottom.

Review Recording Forms - After each page of the recording form is filled with sketches and panel measurements by the ground surveyor, use the form as an aid in finding all the panels of each cluster. Any disagreements over how the cluster was split into panels, missed panels, facing, etc. should be resolved.

It may be helpful to use the margin of the recording form as a checklist. When you feel you have taken a good image of a panel or cluster overview, check it off. You can use the checklist to be sure that you return to take additional images of those panels that require special attention later -- afternoon sun, cloud cover, assistance in holding back branches, sunshades, etc.