1、Designation: E 2566 08Standard Test Method forDetermining Visual Acuity and Field of View of On-BoardVideo Systems for Teleoperation of Robots for UrbanSearch and Rescue Applications1This standard is issued under the fixed designation E 2566; the number immediately following the designation indicate
2、s the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the measurement of se
3、veral keyparameters of video systems for remote operations. It isinitially intended for applications of robots for Urban Searchand Rescue but is sufficiently general to be used for marine orother remote platforms. Those parameters are (1) field of viewof the camera system, (2) visual acuity at far d
4、istances withboth ambient lighting and lighting on-board the robot, (3)visual acuity at near distances, again in both light and darkenvironments, and (4), if available, visual acuity in both lightand dark environments with zoom lens capability.1.2 These tests measure only end-to-end capability, that
5、 is,they determine the resolution of the images on the displayscreen at the operator control unit since that is the importantissue for the user.1.3 This test method is intended to be used for writingprocurement specifications and for acceptance testing forrobots for urban search and rescue applicati
6、ons.1.4 This test method will use the Snellen fraction to reportvisual acuity; readers may wish to convert to decimal notationto improve intuitive understanding if they are more familiarwith that notation. Distances will be given in metres withEnglish units in parentheses following.1.5 This standard
7、 does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Terminology2.1 Definitions:2.
8、1.1 field of view, nangle subtended by the largest objectthat can be imaged with the video system.2.1.2 optotype, ncharacter used on a chart for testingvisual acuity.2.1.2.1 DiscussionOptotypes are generally built ona5by5 grid, with the size for “standard” vision subtending a square5 min of arc on a
9、 side. This makes one grid element 1 min ofarc square.2.1.3 tumbling E, nspecific optotype that can be drawn invarious orientations (facing left, right, up, or down) and invarious sizes to create an eye chart (see Fig. 1).2.1.3.1 DiscussionThis optoptype is reported in the litera-ture as being maxim
10、ally distinguishable. Eye charts withTumbling Es are available commercially for use at differentdistances.2.1.4 standard vision, nability to resolve target featuressubtending 1 min of arc.2.1.5 visual acuity, nability to resolve features subtendingsome angle, as compared with “standard” vision measu
11、red atthe same distance.2.1.5.1 DiscussionAn angle Q subtends a feature of size hat a distance d, of size 2h at a distance of 2d, of size 3h at adistance 3d, and so on. If 2d is the “standard” measurementdistance of 6 m (20 ft), an eye chart for use at 3 m (10 ft) wouldhave characters of h high rath
12、er than 2h high and themeasurement of visual acuity would be the same. See Fig. 2 foran illustration of the angle/distance relationship.2.1.6 Snellen fraction, na measure of visual acuity.2.1.6.1 DiscussionThe subject is placed a standard dis-tance from an eye chart, typically 6 m (20 ft). The subje
13、ct isasked to identify the line with the smallest characters that hecan resolve. The Snellen fraction is the ratio of the distance atwhich that line would be resolved by a subject with standardvision to the standard test distance. Thus, a subject withstandard vision would have 6/6 (20/20) vision.2.1
14、.7 remote operation, nact of controlling a distant roboton a continuous or intermittent basis via tethered or radio-linked devices while being provided with sensory information(for example, visual information through cameras onboard therobot).1This test method is under the jurisdiction of ASTM Commi
15、ttee E54 onHomeland Security Applications and is the direct responsibility of SubcommitteeE54.08 on Operational Equipment.Current edition approved Feb. 1, 2008. Published March 2008.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.2.1
16、.7.1 DiscussionRemote operation includes teleopera-tion as well as forms of intermittent autonomy or assistedautonomy.3. Units for Reporting Visual Acuity3.1 The commonly used distance for measuring visualacuity is 20 ft in the United States. This leads to the “Snellenfraction” as the common measure
17、 of visual acuity: 20/20,20/40, and so on. The Snellen fraction is also used in England,referred to 6 m as the standard measurement distance (6/6,6/12, etc.), while the rest of Europe generally used the decimalfraction equivalent: 20/20 = 6/6 = 1.0; 20/40 = 6/12=0.5, etc.Measurements may be taken at
18、 any distance and the resultscaled to the common distance.3.2 The meaning of 6/12 (20/40 or 0.5) is that features thatcan be resolved at 6 m (20 ft) by the test subject are of a sizesuch that a person with “standard” visual acuity could resolvethem at 12 m (40 ft). The characters on the 6/12 (20/40,
19、 0.5)line of an eye chart are twice the size of the characters on the6/6 (20/20, 1.0) line. The best human vision is not 6/6 (20/20,1.0), resolving 1 min of arc (1/60 = .016) but more like 6/3.6(20/12, 1.7), resolving about 0.01.4. Significance and Use4.1 Responder-defined requirements for these tes
20、t methodsare documented in a preliminary document entitled “Statementof Requirements for Urban Search and Rescue Robot Perfor-mance Standards.”24.2 Field of View is important in terms of the ability of theoperator to drive the robot. Looking at the world through azoom lens is like “looking through a
21、 soda straw.” Looking witha 30 or 40 field of view lens is like “driving with blinders on.”On the other hand, using a very wide field of view lens (witha field of view of 120 or 150), the operators use of optic flowto cue depth perception is severely degraded and navigating ina tight environment is
22、very difficult. Multiple cameras arerecommended, with one providing a very wide field of view orall together providing a very wide field of view.4.3 Far Vision Visual Acuity is important for both un-manned air vehicles (UAVs) and ground vehicles for wide areasurvey. Zoom is required for ground vehic
23、les for wide areasurvey.4.4 Near Vision Visual Acuity is important for groundvehicles for wide area survey in examining objects at closerange and also for small robots which operate in constrainedspaces.4.5 Testing in the dark is important for small robots sincethey must sometimes operate in spaces
24、with no ambientlighting.5. Hazards5.1 There are no hazards and no environmental issuesassociated with this test method.6. Procedure6.1 Field of View:6.1.1 The test environment for 6.2 below is established,with eye charts on a wall and the robot located at a set testdistance 6 m (20 ft) away from the
25、 wall (see Fig. 3). Verticallines are drawn on the wall subtending fields of view from thetest distance of 20 to 60 (or more if space allows) inincrements of 10 and labeled.6.1.2 Taking the line from the robot camera to the center ofthe eye chart as the center line, field of view lines need only bed
26、rawn to one side because of symmetry.6.1.3 Determine field of view and record the result.6.1.4 If the camera lens has a field of view beyond 60, andtest site space does not allow further reference marks, the fieldof view can be calculated using trigonometry (see Fig. 4).Field of View 5 2 f52 tan1h/d
27、!6.1.4.1 Beyond 100 h becomes very large and usingtrigonometry may be impractical. The vendor will generallyknow the field of view of the lens provided with the camera, oran estimate may be made. High precision is not important indetermining the field of view since this only provides an2Messina, E.,
28、 et al., “Statement of Requirements for Urban Search and RescueRobot Performance Standards,” http:/www.isd.mel.nist.gov/US 2.0 to 0.1 or 0.07). The optotypes thus subtend 2.5 minof arc at the smallest to 50 or 75 min of arc at the largest. Asnoted earlier,a3meyechart can be used at 6 m and the resul
29、tsscaled (the 6/6 line on a chart designed for 3 m represents 6/3acuity when used at 6 m). If necessary, larger optotypes can beprinted to extend the measurement range to 6/180 (20/600;0.03), at which point the optotoypes would subtend 2.5. If therobot has zoom capability, a close range eye chart (f
30、or testingreading ability, typically for use at 40 cm (16 in.) should bemounted below the larger eye chart. Using the 40 cm chart at6 m and successfully reading the 6/4.5 (20/15, 1.33) line withFIG. 3 Test of Visual Acuity and Field of ViewFIG. 4 Geometry of Field of View DeterminationE 2566 083a zo
31、om lens would be equivalent to 6/0.3 (20/1, 20.0) visionsince 600/40 = 15; 15 3 1.33 = 20.0.6.2.3 The robot is placed so that the camera under test is 6m (20 ft) from the eye charts. The lowest line that can be readon the operator control unit screen without zoom is determinedand recorded.6.2.4 If t
32、he robot has a zoom lens, the lens is run tomaximum zoom and the lowest line that can be read isrecorded.6.2.5 When mpeg coding is used for video compression, theoperator should report only the lowest line at which all fourbars of the “E” are distinguishable. The discrete cosinetransform used in mpe
33、g coding highlights the asymmetric sidebar of the “E” with the lowest spatial frequency filter andallows interpretation of the orientation of the characters belowthe level at which the character can actually be distinguished.Care should be taken not to introduce a bias in this case.6.3 Visual Acuity
34、Near Vision with Ambient Illumination:6.3.1 This test establishes the ability of the operator to usethe robot to examine objects at close distances.6.3.2 An eye chart designed for testing visual acuity forreading is used. The typical test distance is 40 cm (16 in.).6.3.3 Place the eye chart at the d
35、istance for which it wasdesigned from the camera. The eye chart should be mounted atthe height of the camera. Illumination at the eye chart shouldbe 1000 lux.6.3.4 Read the lowest line that can be distinguished on theoperator control unit screen and record the result.6.3.5 Use the zoom and read the
36、lowest line that can beresolved and record the result. Zoom lenses can lose focus atclose ranges, so only a portion of the full zoom capability willbe available.6.3.6 As noted above, only the line at which all four bars ofthe “E” can be distinguished should be reported.6.4 Visual AcuityFar Vision wi
37、th Illumination from theRobot:6.4.1 This test determines the visual acuity available to theoperator at the operator control unit when the robot is operatingin the dark.6.4.2 The same test as 6.2 is run in a dark environment(ambient illumination at the eye chart of 1000 lux, which corresponds totypic
38、al good indoor lighting.8.3.2 A second source of bias is introduced when mpegcoding is used for compressing the video for transmission. Thediscrete cosine transform used in mpeg coding picks up theasymmetric side bar of the “E” with the lowest spatialfrequency filter and allows interpretation of the
39、 orientation at alevel below which the four bars of the “E” can be distin-guished. This is particularly noted when the camera lens haszoom capability as operators are observed moving the zoomback and forth to match the spatial filter size to the charactersize. As noted in Section 6, the operator mus
40、t be directed toreport only the level at which all four bars of the “E” charactercan be distinguished.9. Keywords9.1 field of view; remote operation; robots; teleoperation;urban search and rescue; video systems; visual acuityE 2566 084FIG. 5 Example Data Collection Form for Visual Acuity and Field o
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44、wn to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).E 2566 086
