Differences between revisions 8 and 9
Revision 8 as of 2011-04-19 01:55:41
Size: 18425
Editor: shoobe01
Comment:
Revision 9 as of 2011-04-19 02:07:27
Size: 14656
Editor: shoobe01
Comment:
Deletions are marked like this. Additions are marked like this.
Line 8: Line 8:
 * '''Cell''' --  * '''Cell''' -- The location of the BTS (cell tower) is well-known, and its ID is attached to the call record. The actual precision varies, but a good rule of thumb is to assume the device is in a circle 3000 yds m across.
Line 10: Line 10:
Mobile telephony is based on communications and handoff between cells, each of which is (generally) controlled by a single tower with multiple antennas. The tower location is well-known, and its ID is attached to the CDR, so it can be detected.  * '''Sector''' -- The sector (antenna pointing a specific direction) on the cell can be detected by the operator (i.e. not while roaming). This provides a much smaller area, around 1200 m across. Yes, sectors are not circles, but it's dificult to communicate shape and orientation, so this is close enough.
Line 12: Line 12:
This is a fallback, when other things are not available. Better technologies are generally not available when roaming, and the data is not or cannot (technology or politics) shared at more precision with your home network or because you are from another operator.  * '''Triangulation''' -- Triangulation is the practice of determining the location of a point by measuring the angle and/or distance from several known locations. More points give more precision. Methods of triangulating with radio get really complex and vary by network type and equipment available. Precision varies, and is generally included with the result by the network service calculating the location. 12 yard precision is possible, but 50 m is more likely.
Line 14: Line 14:
Precision will vary widely by the size of the cell, and there is no (good, universally-accepted) method to determine and communicate precision and accuracy. A good rule of thumb – and something similar is generally used by devices – is a circle 3000 yds (m) across.  * '''GPS Telemetry''' -- The ubiquitous satellite-based network. Portable, hand-held receivers like those in mobile handsets can generally be assumed to give precision of 20-50 ft, though antenna and signal processing improves constantly and precision can be in single digit feet. Others, such as Galileo, GLONASS and COMPASS may also be included in general mobile devices, and will operate in similar ways. In theory, eventually, using multiple unrelated systems will give better accuracy yet, and give better coverage when in touchy situations like in dense cities.
Line 16: Line 16:
 * '''Sector''' --  * '''WAAS''' -- WAAS is a satellite based augmentation system based in North America (others exist in the rest of the world, but are less well-established) that sends additional signals via another set of satellites to allow GPS receivers to adjust for those inaccuracies. I know of no mobile phones that have a built-in WAAS receiver, but it's a location technology that does exist, and is employed on cell towers using AGPS.
Line 18: Line 18:
Recall that each tower has multiple antennas. Those three (or four, rarely anything else, depends on the carrier) antennas point different directions. Each of those is an independent mobile radio sector; just like signals are handed off between cells, they are handed off between sectors, and the data is generally known to the handset and can sometimes be shared with services or providers. However, since the direction the sector faces is really only known to the company that installed it, and the network operator, they are the only ones that can use the data well. Precision will vary widely by the size of the cell, and by the antennas used, the number on the cell, the down-angle, and so on. There are some semi-useful ways of determining precision and accuracy for a single read, but they are not univerally implemented and there is no way to send the data to the information providers (e.g. the map program). A good rule of thumb – and something similar is generally used by devices – is a circle 1200 yds (m) across, co-located with the radio centroid of the sector. Yes, sectors are not circles, but it's also hard to communicate shape and orientation, so this works.  * '''AGPS''' -- Assisted GPS sends part of the GPS signal to the device over the mobile network connection in order to provide additional precision, and speed the startup time of the GPS to as good as a few seconds. AGPS is not generally selectable as a separate service; when the user chooses to turn on or off "GPS," and has a network connection (and an AGPS compliant phone, etc.) they get the advantages of AGPS.
Line 20: Line 20:
 * '''Triangulation''' --  * '''WLANs & PANs''' -- Local networks like WiFi and Bluetooth are localized radio technologies, and can add another layer of location, so could increase precision. They can also be used instead of other technologies when there is no GPS signal, or a bad mobile signal so triangulation cannot be used.
Line 22: Line 22:
Generally, triangulation is the practice of determining the location of a point by measuring the angle and/or distance from several known locations. More points give more precision. It can get more complex when you try to find points in 3D space, but all mobile triangulation systems mostly assume the earth is locally perfectly flat, and simply find the location on the geoid. Methods of triangulating get really complex and vary by network type and equipment available; multilateration and signal interpolation are some of those. The math can get pretty harrowing. Precision varies mostly by the number of sectors being used, the distance between them and other variables of the network. There may be a method of communicating to services employing it an approximation of the precision available. In any remotely built-up area, where it most often has enough sectors to work, a circle 50 yds (m) across is typical. 12 yd precision is possible, with good accuracy. Both of these currently use the "cell" (or network identifier) and triangulation methods described above.
Line 24: Line 24:
 * '''GPS Telemetry''' -- They are both relatively more rare, and often are supported by third party software or individual services (which may have specific capabilities), and are not universally implemented on the handset. There are no reliable, independently verified numbers on the real-world precision, but tests of WiFi triangulation alone have gone down to inches. On the other hand, poor network identification has led to placing users on the wrong continent.
Line 26: Line 26:
The Global Positioning System consists of a ground based control system, a series of satellites and any number of anonymous receivers. So, reading that alone dismisses many misconceptions; its one-way, it's a system, and the signal is from satellites and has nothing to do with mobile networks.

Telemetry means data sent from a remote (usually mobile) site like a rocket, back to base. Here, it means the device figures out where it is by listening to the satellites, then tells the network or website or whatever where it is.

Ignoring SA, GPS can give precision to fractions of an inch at least. But those are large, complex devices used for special surveying and scientific tasks. Portable, hand-held receivers like those in mobile handsets can generally be assumed to give precision of 20-50 ft, though antenna and signal processing improves constantly and precision can be in single digit feet.

There are other systems, like Galileo, GLONASS, and COMPASS but none of these are really fully-active, and there are few or no receivers in mobiles as yet. In theory, eventually, using multiple unrelated systems will give better accuracy yet, and give better coverage when in touchy situations like in dense cities.

 * '''WAAS''' --

GPS uses radios, and the atmosphere and earth are imperfect and can displace or distort the signals. WAAS is a satellite based augmentation system based in North America (others exist in the rest of the world, but are less well-established) that sends additional signals via another set of satellites to allow GPS receivers to adjust for those inaccuracies. I know of no mobile phones that have a built-in WAAS receiver, but it's a location technology that does exist, and is employed on cell towers using AGPS.

 * '''AGPS''' --

Assisted GPS requires the use of mobile networks, so only works when in data communication range. The cell tower has its own GPS (which many use anyway to get precise time codes), and usually a WAAS receiver. This provides a bit more precision, assures it of more accuracy, but mostly helps speed up cold or warm starts. Briefly, for a GPS to work, the receiver has to download data about all the satellites before it can calculate the position. AGPS caches this info for the phone, and sends over just the relevant bits, cutting minutes to a second or two.

This is a reason you may not see WAAS, and might see some benefits from other GNSS (say, GLONASS) before the receivers are added to the handsets. AGPS generally gives precision, even in dense areas and on the move, of 10 ft or better. Two foot indicated precision has been observed.

AGPS is not generally selectable as a separate service; when the user chooses to turn on or off "GPS," and has a network connection (and an AGPS compliant phone, etc.) they get the advantages of AGPS.

 * '''WLANs & PANs''' --

Local networks like WiFi and Bluetooth are not exactly more precise,but are at the bottom of this list because they are local, and can add another layer of location, so could increase precision. They can also be used instead of other technologies when there is no GPS signal, or a bad mobile signal so triangulation cannot be used.

Both of these currently use the "cell" (or network identifier) and triangulation methods described above. There are no sectors, and no universally-adopted AGPS system to work with device telemetry. Naturally, a handset getting good GPS data can send that telemetry to anyone over any network, including WiFi, but that's not the same thing.

They are both relatively more rare, and often are supported by third party software or individual services (which may have specific capabilities), and are not universally implemented on the handset. There are no reliable, independently verified numbers on the real-world precision, but tests of WiFi triangulation alone have gone down to inches. On the other hand, poor network identification has led to placing users on the wrong continent. There's room to improve here.

 * '''Ask''' --

People often know where they are. If you cannot get any location, or there's a reason they might want to over-ride it (even as simple as the data is bad) let them enter a location. If you do this, allow lots of methods. Only accepting ZIP or postal code is not useful for e.g. travellers, who do not generally know the ZIP where they are.

 * '''Ask''' -- People often know where they are. If you cannot get any location, or there's a reason they might want to over-ride it (even as simple as the data is bad) let them enter a location. If you do this, allow lots of methods. Only accepting ZIP or postal code is not useful for e.g. travellers, who do not generally know the ZIP where they are.
Line 127: Line 95:
 * 56th Street & Russell Ave, Mission, Kansas 66202 ''Street or Intersection''
 * West Crossland, Mission, Kansas 66202 ''Neighborhood''
 * Mission, Kansas 66202 ''City''
 * 10 miles west of downtown Kansas City, MO ''Relative Location''
 * Near Kansas City, MO ''Area''
 * 56th Street & Russell Ave, Mission, Kansas 66202 - ''Street or Intersection''
 * West Crossland, Mission, Kansas 66202 - ''Neighborhood''
 * Mission, Kansas 66202 - ''City''
 * 10 miles west of downtown Kansas City, MO - ''Relative Location''
 * Near Kansas City, MO - ''Area''

Problem

Availability of location based service, and the actual location of the handset must be easily and accurately communicated.

Solution

Mobile devices have numerous methods of retrieving location information. These are listed in, approximately, less to more precision, but are not necessarily better or worse otherwise.

  • Cell -- The location of the BTS (cell tower) is well-known, and its ID is attached to the call record. The actual precision varies, but a good rule of thumb is to assume the device is in a circle 3000 yds m across.

  • Sector -- The sector (antenna pointing a specific direction) on the cell can be detected by the operator (i.e. not while roaming). This provides a much smaller area, around 1200 m across. Yes, sectors are not circles, but it's dificult to communicate shape and orientation, so this is close enough.

  • Triangulation -- Triangulation is the practice of determining the location of a point by measuring the angle and/or distance from several known locations. More points give more precision. Methods of triangulating with radio get really complex and vary by network type and equipment available. Precision varies, and is generally included with the result by the network service calculating the location. 12 yard precision is possible, but 50 m is more likely.

  • GPS Telemetry -- The ubiquitous satellite-based network. Portable, hand-held receivers like those in mobile handsets can generally be assumed to give precision of 20-50 ft, though antenna and signal processing improves constantly and precision can be in single digit feet. Others, such as Galileo, GLONASS and COMPASS may also be included in general mobile devices, and will operate in similar ways. In theory, eventually, using multiple unrelated systems will give better accuracy yet, and give better coverage when in touchy situations like in dense cities.

  • WAAS -- WAAS is a satellite based augmentation system based in North America (others exist in the rest of the world, but are less well-established) that sends additional signals via another set of satellites to allow GPS receivers to adjust for those inaccuracies. I know of no mobile phones that have a built-in WAAS receiver, but it's a location technology that does exist, and is employed on cell towers using AGPS.

  • AGPS -- Assisted GPS sends part of the GPS signal to the device over the mobile network connection in order to provide additional precision, and speed the startup time of the GPS to as good as a few seconds. AGPS is not generally selectable as a separate service; when the user chooses to turn on or off "GPS," and has a network connection (and an AGPS compliant phone, etc.) they get the advantages of AGPS.

  • WLANs & PANs -- Local networks like WiFi and Bluetooth are localized radio technologies, and can add another layer of location, so could increase precision. They can also be used instead of other technologies when there is no GPS signal, or a bad mobile signal so triangulation cannot be used.

Both of these currently use the "cell" (or network identifier) and triangulation methods described above.

They are both relatively more rare, and often are supported by third party software or individual services (which may have specific capabilities), and are not universally implemented on the handset. There are no reliable, independently verified numbers on the real-world precision, but tests of WiFi triangulation alone have gone down to inches. On the other hand, poor network identification has led to placing users on the wrong continent.

  • Ask -- People often know where they are. If you cannot get any location, or there's a reason they might want to over-ride it (even as simple as the data is bad) let them enter a location. If you do this, allow lots of methods. Only accepting ZIP or postal code is not useful for e.g. travellers, who do not generally know the ZIP where they are.

Each of these must be understood, be able to be used (as long as the hardware is available) by the system and by each application, and communicate the correct degree of precision and accuracy.

An understanding of the difference between precision and accuracy is also crucial. In brief: precision is the number of decimal places you measure something to; accuracy is how correct it is. The less accurate you think your measurement is, the less precise you should report it.

Privacy and security concerns are beyond the scope of this book, but must be considered when designing location based services. In many countries, there are legislative or regulatory restrictions on enabling and use of location services, so notification of background tracking is a legal requirement, not just best practice.

Location is not the same as Orientation or other types of position information. When these must be communicated -- as for augmented reality -- they are generally deeply integral to the visualization and interactive design of the application. No distinct patterns yet exist for these behaviors, but best practices from aviation may serve to guide designs.

Variations

Location service is often used as a background service, or promote smarter ambient computing,. When directly referred to, it may only be momentarily switched to while other tasks occupy the remaining time. Therefore, both explicit and background indicators cases may be present not just in the same system, but at the same time.

  • Explicit - maps, CEP circles, etc. -- name of city! errors of precision there...

  • Background - notify, behave appropriately... permission (one off and Android-style on-install), annunicator and example of "in a meeting because at the right location at the right time"

Though this pattern discusses such behaviors and features on a mobile device, they may also be used for remote devices in much the same manner. "Child trackers" and similar functions may be used from another mobile device or from desktop computers to track a remote mobile device. In this case, both the viewing terminal and the

Interaction Details

Indicators of state are generally only present in the Annunciator Row and cannot be interacted with. A system setting should be made available to control the use of GPS, WiFi and other controls, as well as to set privacy controls for sharing and how much automatic (vs. manual) control is allowed over these systems.

... FIX "ICON" LABEL ...

An easy method must be provided to access this control, without drilling into multiple sub-menus. Whenever possible, add this control shortcut to any application that uses location services. The control may also be added as an interactive Icon on the Idle Screen for access from any application, or so the user may manually enable the service before it is needed.

Whenever possible, applications or services which are best with location should automatically enable the required hardware. OS level restrictions or user settings may interfere with this behavior, and require user intervention each time. If so, an interstitial Pop-Up is often the best way to request this.

When the Pop-Up itself is restricted from offering a function to enable the GPS (or other hardware), use it sparingly, as a reminder to the user instead, and provide a link to the appropriate settings panel. When settings are changed, always return the user to the originally-requested application.

Only use the precision required for the task at hand. Weather, for example, rarely requires more than city-level precision. The GPS is not required for basic conditions and forecast information.

On the other hand, always present the most relevant details for each view. If the user chooses to view a local radar map, they should not be required to know their location but should be presented it systematically. The weather application may have to turn on and off various location services as the application is used, and should not enable all services when it is opened, or get by with only the minimal set and present less than optimal information.

Presentation Details

When location service is enabled, this should be shown in the Annunciator Row, generally as an icon. The location icon (crosshair) has come to mean GPS is enabled, so there may be challenges in communicating other types of location services. GPS can use other types of icons, such as a satellite dish. GPS requires a short time to find position, and can loose position due to interference, clutter or other conditions, and must display the current status. Generally, animating the satellite dish (implying "scanning for service") works well.

Avoid duplicating indicators. If in the Annunciator Row, there is generally no need to also include such indicators within an application. This is another good reason to preserve Annunciator Row display, instead of loading applications full-screen.

For explicit graphic display of location, such as on a map, a cursor will be used to denote the current position. Note that this is actually the centroid of the CEP or circular error of probability. A probability threshold is programatically established; based on the technology used to determine location, the device is almost certainly located within this circle. (Note, it is impossible to absolutely determine location, hence the "probability" prhasing, but this is not terribly important for general discussions).

This CEP circle should be displayed, with the cursor at the center, as a visual method of communicating the precision of the location technology. Unless additional precision is needed but is currently unavailable, the default view should hide the CEP circle from the user. For a weather map, for example, the default zoom level should be large enough that a 100 m CEP is smaller than the cursor, so disappears under it. Good selection of map zoom level also helps communicate the degree of precision available.

When the display is zoomed such that the CEP circle is at least 10 times the size of the cursor, or the edge is partly or entirely outside the viewport, an explicit display of precision (discussed below) should be printed adjacent to the cursor.

An even greater pitfall in the display of precision information is with printed location, especially in coordinate systems. Whenever possible, use standard, well-understood nomenclature. Avoid printing the location when not useful; lat/long is difficult to interpret and very few general users will understand it.

Precision also must be accounted for. For this example, the MGRS coordinate system will be employed as it is based on simple measurements from a regional baseline. This is unlikely to be employed in general consumer applications, however. A complete location to 1 meter precision is listed as:

15S UD 12345 67890

However, most location technologies, in most instances, cannot give such precision. Digits should be removed until only the correct level of precision is shown. For example, if using cell sector, with precision in the 100 m range, only display

15S UD 123 678

The last digit will always be of less precision than the others, and even when displayed digitally can be used like that on a dial or scale. Simply restrict the display to only the 5 or 0 digits.

Precision should be explicitly displayed when coordinates are printed. Use the existing settings for units of measure, but scale them appropriately. In the following examples, the user has set their navigation tool to use miles.

  • "Accuracy 19 ft" - Correct. Appropriate scale (vs. yards or miles) for the size, and in the same system.

  • "Accuracy 6 m" - Incorrect. In the wrong system of measure.

  • "Accuracy 0.004 mi" - Incorrect. Too large a measure, so many decimals, and not easily understood.

Note that the term "precision" is not well understood, so is often replaced with "accuracy" in general communications, as in the examples above, although it is not strictly true.

Addresses, likewise, should only be displayed when that level of precision is available. Otherwise use existing best practices for general location:

  • 5600 Russell Ave, Mission, Kansas 66202
  • 56th Street & Russell Ave, Mission, Kansas 66202 - Street or Intersection

  • West Crossland, Mission, Kansas 66202 - Neighborhood

  • Mission, Kansas 66202 - City

  • 10 miles west of downtown Kansas City, MO - Relative Location

  • Near Kansas City, MO - Area

Only display the larger scale information such as state and country when needed. When moving between two areas only a few miles apart, the default location display should probably just be the street address portion. The same filtering logic should be used for coordinate systems, when applicable. While Lat/Long is a global system, UTM and MGRS are divided into regions; the "15S UD" portion in the example above can be made much less prominent, as most precision navigation is not also global navigation, so it will not be used as much as the remainder of the displayed coordinates.

Direction of travel should only be displayed when available, and should only display to the degree known. Generally, the cursor will be a pointer to assist with this. For free standing displays, when users will understand, display bearing in degrees, and by named directions (north-east) but degrade to cardinal directions as the system's understanding becomes more poor.

Cardinal directions (e.g. "North") can imply precision if simply printed on the screen; use graphic displays (either dials or circular Tapes) to communicate the degree of precision available, make small changes in bearing angle visible to the user and make the display more glanceable.

When direction of travel cannot be determined (there is no compass and the device is not moving), display no direction of travel indicator, or an icon indicating it is unknown. The cursor may change to circle, or otherwise become blunted to reduce or remove the implication that direction is known. Do not display the last direction, as this is likely to be spurious data arising from loss of signal or stopping.

ROTATE THE MAP TO ORIENT SO FORWARD IS UP; IF YOU CAN'T BRING YOURSELF TO DO THAT BY DEFAULT, OFFER AND OPTION...

Antipatterns

Never equate "location" with "GPS" and only allow the use of location based services with a ... too much precision always bad!

... over-implying precision with crosshairs, etc. ... use CEP circles...

Examples

Location (last edited 2011-12-13 16:53:08 by shoobe01)