Method for organizing and compressing spatial data

Abstract

A method for organizing and compressing spatial data to enable fast, incremental downloads of spatial data over a network. The method comprises multiple steps for segmenting and reducing spatial data, and introduces a location-relevant naming system for storing and accessing the data. Applications installed on remote devices are able to efficiently compute data file names based solely on location information, download the data over a network and cache the data on the device.

Description

Y2-offset=Ly-max
X2-value=N * (x−x2-offset)
Y2-value=N * (y2-offset−y)
N=upper limit of valid integer values (50000 in the preferred embodiment)

The formulas for computing level 1 offsets and values are:
X1-offset=Abs((x−x2-offset)/((Lx-max−Lx-min)/K))
Y1-offset=Abs((y2-offset-y)/((Ly-max−Ly-min)/K))
X1-value=K*N*(x1−x2-offset−x1-offset)
Y1-value=K*N*(y2-offset−y1-offset−y1)
K=segment divisor (8 in the preferred embodiment for level 1 segments)

The formulas for computing level 0 offsets and values are the same as for level 1, except that K equals 64 in the preferred embodiment.

The example shown in FIG. 3 applies the above formulas to convert the geodetic coordinates 37.308805 and −122.843710 in block 30 to level 1 integers 1278 and 12516 respectively in block 35.

Level 2 offsets are shown in 31 and 32, while level 1 offsets are shown in 33 and 34. In the preferred embodiment of this invention, the upper limit N is set to 50000, but it could be a different number. The number should not exceed 65536 or 2^16, allowing it to be stored as a 2 byte integer (a short). The number should not be too low, which would result in a loss of spatial accuracy, because several real numbers would map to the same integer. The loss of accuracy is about 1 meter as implemented in the preferred embodiment of this invention.

Once a data segment has been processed and all real numbers converted to integers, a file name is assigned to the data segment as the last step in block 15 of FIG. 1. Since the computed integer values are only distance values from a given base value or offset, they are not reversible to the original real number value without the offset. A simple and efficient way to supply the necessary offset values is to make them part of a file name. As shown in the example of FIG. 3 block 36, a level 1 segment file name is comprised of a total of 4 numbers representing the 4 offsets used to compute integer values for that segment, as well as a letter to indicate the level, the letter ‘b’ representing level 1. The first number in 36 represents the level 2 latitude offset and the second number in 36 represents the level 2 longitude offset. The third number in 36 represents the level 1 latitude offset, and the fourth number in 36 represents the level 1 longitude offset.

In order to simplify computing requirements, a new geodetic coordinate system is introduced. The North Pole of the earth is at coordinate (0,0) and the South Pole is at (360,360). Unlike in the standard coordinate system, no negative values are used. Every latitude degree in the standard coordinate system corresponds to 2 latitude degrees in the new system. The conversion from the standard to the new coordinate system is accomplished as follows:
New latitude=90−old latitude*2

• • New longitude=old longitude when range is 0° to 180°
  • New longitude=180+(180−old longitude) when range is−180° to 0°

In the new coordinate system, moving south and east always results in greater coordinates, while moving west and north always results in smaller coordinates, until the respective end points 0 and 360 are reached. This system significantly reduces the number of exception checking operations required by map display software when compared to the standard coordinate system.

This shows that the file name contains the offset information for the spatial data stored in the file. Thus, map display software can perform a few simple calculations to compute a file name from any geodetic coordinate, which may be supplied by GPS output. It should also be evident that the task of computing file names for data segments adjacent to a given segment is very straightforward using said file-naming system.

The following section describes how a map display program can use said file system and offer desirable functionality such as combined online/offline operation. In a typical embodiment, the map display program is installed on a wireless device such as a smartphone or personal digital assistant. As shown in FIG. 4, a map display system 40 consists of several functional components. The input interface layer 44 handles communication with the user or device. A text-input component lets the user type location information such as an address, a city, a zip code or a start/end point of a trip. The input interface 44 transmits said location information over the network to a geocoding engine 48 residing on a server 47. As is well known in the art, a geocoding engine computes a geodetic coordinate (longitude/latitude) from said information. Once the input interface 44 receives said geodetic coordinate from the geocoding engine 48, it notifies the map display engine 46. Some devices may have voice recognition capabilities. Instead of typing the user speaks said location information. The input interface 44 transmits the information from the voice recognition system 42 to the geocoding engine 48, waits for an answer and forwards it to the map display engine 46. Some devices may have a GPS receiver attached to or incorporated into the device. The input interface 44 processes the GPS output and relays said output to the map display engine 46 without the need to communicate with the geocoding engine 48.

The map display engine 46 uses said geodetic coordinates received from the input interface 44 to calculate four file names. The input interface 44 also tells the map display engine 46 which data level is needed, e.g. high-resolution level 0 is appropriate when the user specified an address, while level 1 may be more appropriate when the user specified a city or zip code. As has been shown in detail in a previous section, a geodetic coordinate can be decomposed and produce a unique file name. The map display engine 46 could then request said file name from a server 47 on which all files 49 are stored. However, in the preferred embodiment, the map display engine actually computes a total of four file names. If only one file is fetched, the geodetic coordinate of interest to the user could be located somewhere near the edge of said file. It would look awkward to the user and be less informative if the point of interest is not shown at or near the center of the map display screen. The ability to center the map picture has been lost by segmenting the spatial database. The solution employed by the map display engine 46 is to fetch three additional data segment files, which are most adjacent to said geodetic coordinate. The map display engine simply determines into which area, top-left, top-right, bottom-left or bottom-right, said coordinate falls. If a point falls in the top-left quadrant of a file, as does point 54 in FIG. 5, the map display program first finds file 105.237.3.1.b shown in block 53, and then also fetches the file to the top, block 51, to the left, block 52, and to the top-left, block 50. After fetching all 4 files from the server 47, the map display engine combines the data of the 4 files using simple offset calculations before drawing the map picture to the screen. Said geodetic coordinates can now be displayed fairly close (within 25%) of the screen center. An even better center approximation could be achieved by using nine files. Perfect centering can be achieved by not showing a map picture of the entire available data, but instead generate a slightly zoomed-in map picture centered at said coordinate.

One objective of the invention is to provide a flexible mapping system in the sense that the map display system can function online as well as offline. Offline functionality is desirable because it offers the highest speed, since the data is accessed from local storage. The map display engine 46 gives users several options to enable offline capability. Users can select a city or zip code and download all data files for said city or zip code. Furthermore, users can reserve a certain amount of local disk space to be allocated for map data caching. When caching is enabled, the map display engine 46 automatically stores downloaded files on the local disk. As the cache fills up, new data files replace the least frequently accessed data files. A different caching algorithm, for instance based on last accessed time stamps, could be used as well. When the user has selected caching or preloading of data, the map display engine 46 always first scans the local disk space and, if available, loads data files from local space into memory instead of downloading said files from a remote server. Local caching is very useful when users frequently request the same maps. For instance, a user may want to check road traffic conditions on a daily basis. In this case, only updated traffic information such as traffic incident locations or traffic speed maps (a list of measured traffic speeds at different locations) needs to be downloaded. Said updated traffic information can be displayed on a map, which is generated from the map display engine 46 using local map data. Said offline/online capability offers optimal performance for frequently used maps as well as great flexibility regarding local storage capacities of different devices.

While the invention has been described in connection with a preferred embodiment, it is not intended to limit the scope of the invention to the particular form set forth, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

Claims

1. A method for organizing spatial data comprising the steps of:

a) parsing the spatial data into a plurality of packets;

b) segmenting the packets;

c) reducing a size of the packets by eliminating at least one data point from at least one display element by applying an angle comparison between an adjacent display element, wherein the at least one data point is eliminated if an angle between the at least one display element and the adjacent display element is about 180°; and

d) generating a name for each of the packets.

2. The method of claim 1, wherein the spatial data comprises topographic information comprising a plurality of elements containing geodetic coordinates.

3. The method of claim 1, wherein the step of parsing the spatial data comprises:

selecting at least one entity within the data, the entity selected from a group consisting of: a road, a railway, an airport, a river, a lake, a shore line, a park, an entity comprising a geometric shape, and an entity comprising a substantially rectangular shape.

4. The method of claim 1, wherein the step of parsing the spatial data comprises:

generating a substantially rectangular element comprising about 1° longitude and about ½° latitude.

5. The method of claim 1, wherein the step of parsing the spatial data comprises: separating a topographic element from an attribute element;

wherein the topographic element comprises elements expressed using a geodetic coordinate system; and

the attribute element is related to the topographic element.

6. The method of claim 1, wherein the step of segmenting the packets comprises:

dividing the packets into at least one element, the element selected from a group consisting of: an 8×8 grid, a 64×64 grid, a substantially rectangular grid comprising about 1° longitude and about ½° latitude, and a substantially rectangular grid comprising about ⅛° longitude and about 1/16° latitude.

7. The method of claim 1, wherein the step of reducing the size of the segmented packets comprises:

eliminating elements selected from a group consisting of: a polygon, a lake, a geographic area, a topographic element and an attribute element.

8. The method of claim 1, wherein the step of reducing the size of the segmented packets comprises:

eliminating a plurality of data points from a topographic element.

9. The method of claim 1, wherein the step of reducing the size of the segmented packets comprises:

transforming a geodetic coordinate from a real number to an integer number, wherein the integer number ranges from about 0 to about 65535.

10. The method of claim 1, wherein the step of reducing the size of the segmented packets comprises:

eliminating a plurality of data points from at least one topographic element by applying an angle comparison between an adjacent topographic element line, wherein at least one data point is eliminated if an angle between the at least one topographic element and the adjacent topographic element line is about 180°.

11. The method of claim 1, wherein the step of generating the name for each of the packets comprises the step of generating a location-relevant naming system.

12. The method of claim 1, wherein the step of generating the name for each of the packets comprises the step of generating a location-relevant naming system, wherein the packet name comprises location information representing an offset from an earth origin.

13. The method of claim 12, wherein the earth origin is selected from a group consisting of: a North Pole, and a location other than the North Pole.

14. The method of claim 1, further including the step of: repeating any one of steps a, b, c and d to process an entire spatial database.

15. A method for displaying a map, the method comprising the steps of:

obtaining information relating to a location;

calculating at least one packet name;

determining a data level;

displaying the map; and

caching at least one packet until an amount of computer storage space is filled, and

determining which packets should be replaced.

16. The method of claim 15, wherein the step of calculating the at least one packet name comprises:

computing the at least one data packet name using a geodetic coordinate.

17. The method of claim 15, wherein the step of calculating the at least one packet name comprises:

calculating a request location; and

using the request location to calculate the at least one packet name.

18. The method of claim 15, wherein the step of calculating the at least one packet name comprises:

computing four adjacent data packet names;

fetching the packets from a server; and

combining an information contained in the packets to generate a map.

19. The method of claim 15, wherein the step of determining the data level comprises:

determining a resolution level selected from a group consisting of: an address, a city, a zip code and a building floor plan.

20. The method of claim 15, further including the step of:

caching at least one data packet until an amount of computer storage space is filled, and

determining which packets should be replaced.

21. The method of claim 15, further including the step of:

checking a local cache before requesting a data packet from a remote device.

22. A method for organizing spatial data comprising the steps of:

a) means for parsing the spatial data into a plurality of packets;

b) means for segmenting the packets;

c) means for reducing a size of the packets by eliminating at least one data point from at least one display element by applying an angle comparison between an adjacent display element, wherein the at least one data point is eliminated if an angle between the at least one display element and the adjacent display element is about 180°; and

d) means for generating a name for each of the packets.

23. A method to reduce data in a digital map, comprising:

suppressing selected geographic features; and

reducing resolution of remaining geographic features,

wherein the reducing comprises eliminating data points, provided that an angle between two lines connecting a data point to its adjacent data points does not exceed a predetermined angle.

24. The method of claim 23, wherein the selected geographic features include secondary roads.

25. The method of claim 23, wherein the remaining geographic features include primary roads.

26. The method of claim 23, wherein the elimination of data points does not significantly change the overall shape of a remaining geographic feature.

27. A system for reducing data in a digital map, comprising:

means for suppressing selected geographic features; and

means for reducing resolution of remaining geographic features, wherein the reducing comprises eliminating data points, provided that an angle between two lines connecting a data point to its adjacent data points does not exceed a predetermined angle.

28. The system of claim 27, wherein the selected geographic features include secondary roads.

29. The system of claim 27, wherein the remaining geographic features include primary roads.

30. The system of claim 27, wherein the elimination of data points does not significantly change the overall shape of a remaining geographic feature.

31. A non-transitory computer readable storage medium having stored thereon instructions that when executed by a computer processor perform a method of reducing data in a digital map, the method comprising:

suppressing selected geographic features; and

reducing resolution of remaining geographic features, wherein the reducing comprises eliminating a data points, provided that an angle between two lines connecting the data point to its adjacent data points does not exceed a predetermined angle.

32. The non-transitory computer readable storage medium of claim 31, wherein the selected geographic features include secondary roads.

33. The non-transitory computer readable storage medium of claim 31, wherein the remaining geographic features include primary roads.

34. The non-transitory computer readable storage medium of claim 31, wherein the elimination of the data points does not significantly change the overall shape of the remaining geographic features.

35. The method of claim 23, wherein the predetermined angle is greater than 180 degrees.

36. The system of claim 27, wherein the predetermined angle is greater than 180 degrees.

37. The non-transitory computer readable storage medium of claim 31, wherein the predetermined angle is greater than 180 degrees.

38. A method for reducing data in a digital map, the method comprising:

suppressing selected geographic features; and

reducing resolution of remaining geographic features by eliminating at least one data point between two adjacent data points only if an angle formed between a first line and a second line does not exceed a predetermined angle, the first line extending through the at least one data point and one adjacent data point of the adjacent data points and the second line extending through the at least one data point and another adjacent data point of the adjacent data points.

39. The method of claim 38, wherein the reducing comprises eliminating a plurality of selected data points where, for each of the plurality of selected data points, an angle between a first line extending through the selected data point and a first adjacent data point and a second line extending through the selected data point and a second adjacent data point does not exceed the predetermined angle.

40. The method of claim 39, wherein the selected geographic features include secondary roads.

41. The method of claim 39, wherein the remaining geographic features include primary roads.

42. The method of claim 39, wherein the elimination of the at least one data point does not significantly change the overall shape of the remaining geographic features.

43. A system for reducing data in a digital map, the system comprising:

means for suppressing selected geographic features; and

means for reducing resolution of remaining geographic features by eliminating at least one data point between two adjacent data points only if an angle formed between a first line and a second line does not exceed a predetermined angle, the first line extending through the at least one data point and one of the adjacent data points and the second line extending through the at least one data point and another adjacent data point.

44. The system of claim 43, wherein the means for reducing comprises means for eliminating a plurality of selected data points where, for each of the plurality of selected data points, an angle between a first line extending through the selected data point and a first adjacent data point and a second line extending through the selected data point and a second adjacent data point does not exceed the predetermined angle.

45. The system of claim 43, wherein the selected geographic features include secondary roads.

46. The system of claim 43, wherein the remaining geographic features include primary roads.

47. The system of claim 43, wherein the elimination of the at least on data point does not significantly change the overall shape of a remaining geographic feature.

48. A non-transitory computer readable storage medium that stores instructions that, when executed by a machine, cause the machine to reduce data in a digital map, the instructions causing the machine to perform steps comprising:

suppressing selected geographic features; and

reducing resolution of remaining geographic features by eliminating at least one data point between two adjacent data points only if an angle formed between a first line and a second line does not exceed a predetermined angle, the first line extending through the at least one data point and one of the adjacent data points and the second line extending through the at least one data point and another adjacent data point.

49. The non-transitory computer readable storage medium of claim 48, wherein the reducing comprises eliminating a plurality of selected data points where, for each of the plurality of selected data points, an angle between a first line extending through the selected data point and a first adjacent data point and a second line extending through the selected data point and a second adjacent data point does not exceed the predetermined angle.

50. The non-transitory computer readable storage medium of claim 48, wherein the selected geographic features include secondary roads.

51. The non-transitory computer readable storage medium of claim 48, wherein the remaining geographic features include primary roads.

52. The non-transitory computer readable storage medium of claim 48, wherein the elimination of the at least one data point does not significantly change the overall shape of the remaining geographic features.