An application example

1.1 The experimental area selected

In accordance with "9. 5" key scientific and technological projects of the deployment, set up a special topic to study, "dynamic monitoring of resources and environment at the county level technology demonstration," having zoning XX suburban districts and counties selected as the urban and rural areas occupies a kind of demonstration, the focus study of RS, GIS and GPS integration of technology in the dynamic monitoring of land resources in the application.

XX suburb located in the north temperate inland arid area farming and animal husbandry ecotone is XX City and its surrounding suburbs in general. Due to the rapid expansion of cities, suburbs of non-agricultural land increase, to the relatively complex and changing fast. How to quickly grasp the urban and rural occupies a land-use change and development trend has been the XX Urban Planning and Land Authority to address the management issues. Select the region as a dynamic monitoring of resources and environment at the county level technology demonstration areas, on the one hand conform to local needs; the other hand, rural terrain is relatively flat, enabling measurement of the GPS field, and the South is relatively simple compared to crop species, using remote sensing to detect changes relatively easy. In addition, the suburban county land survey results of high quality.

1.2 GIS data layers to this at the end of the establishment of

Outskirts of the total area 2205.9 km2, land survey work was completed in 1992, through the acceptance as the outstanding achievements of the autonomous region. Survey map the region of 1:1 million, according to the standard rate increase is 126 points. All use of scanner input, after editing, the establishment of land survey historical database.

1.3 variation spots (land) Identification of

1.3.1 Remote sensing data processing and its relationship with land survey data, registration

Select August 4, 1996 XX City area of the TM image, select 3,5,4 3-band image enhancement for the control of 1:1 10000 topographic maps selected 21 features in points as image geometric rectification control points to geometric correction. In vivo using bilinear interpolation of the gray value of re-sampling, depth database of land in the 1:1 million in 1992 land use data and remote sensing images with quasi-stack.

1.3.2 Identification of changes in the region

As the traditional land management can only passively land figures reported by the land department, there are false positives, reporting, and hence the problem, but also for changes in the nature of land space is not clear. Using remote sensing tools can take the initiative to find changes in the regional, spatial location at a glance. Given the current automatic classification of remote sensing images, the accuracy of the computer is not high and making full use the experience and knowledge, the use of interactive digital screen changes in the region extraction method. Specifically, this: The post-superimposed on the image displayed on the screen, through the interpretation of human-computer interaction changes found in plots with different colored symbols mark out (including property). Interpretation of the results when completed, will playback output for the use of GPS field measurements.

County, in the suburbs before the next Township, the pilot proved that with the TM remote sensing image can be found in a good land-use changes. Given the fact that the actual changes in land for the 106, by means of remote sensing was found 98, of which 10 are difficult to detect the use of artificial means of remote sensing instruments easier to find. For the small size, remote-sensing methods can not be found in the land, to land departments reported data shall prevail.

1.4 GPS data acquisition 3.4.1 GPS Selection

GPS receivers currently on the market can be divided into navigation by end-use type, type and timing geodesic-type and other types. Has not yet specifically for the production of cadastral survey of the GPS receiver, so we use the GPS receivers are navigation type. GPS receiver manufacturers have produced dozens of domestic market sales are Trimple, Magellan, Garmin, Novtel and so on, they produce GPS receivers have their own characteristics. Taking into account the need for dynamic monitoring of land, should meet the following requirements: ① a higher positioning accuracy, differential treatment must meet m level; ② receiver memory must be large enough to meet the requirements of dynamic measurement field; ③ simple, easy to grasp; ④ differential processing software features a strong addition to high-precision differential treatment, but also to provide and commonly used GIS software, data interfaces.

Based on the above principles, the research group, after careful comparison, select Magellan's ProMark X-CM-based GPS receiver. The aircraft is the more advanced GPS receiver, to receive L1 carrier and C / A code observables is available through the carrier phase and code pseudorange positioning. To carry out sub-carrier phase pseudorange code measurements and differential measurements, ranging from centimeter to meter-scale (<2 m) of the differential positioning accuracy. Machine memory, 4 megabytes, can record data 30 hours of continuous observation (pseudo-range code) and 8 hours (carrier phase), continuous operation of the field is very beneficial.

1.4.2 The establishment of base station

In the outskirts of the city before the next Township XX pilot the use of three sets of ProMark X-CM-GPS receiver, one of Taiwan as a base station, another two sets as a mobile station measurements. Base station must be a point of known coordinates, base station measurement time period must include a mobile station measurement time period, so that there are sufficient data for the use of differential calculations. Township in the suburbs before the next trial, the base station chosen terrain is relatively high, there is no shelter around the martyrs cemetery in the vicinity of the GPS mapping control points. If you can not find the right coordinates are known accurately known points (control points, such as surveying and mapping), GPS receivers can be used for static position for longer-term observation, to strike a known point, and then use this point as the base station.

1.4.3 changes in the boundary coordinates of points of access to land

Having set the base station for mobile stations can be dynamic measurement, to obtain changes in the boundaries of plot coordinates. The GPS antenna mounted on a light pole on the antenna support, hand-held GPS receiver along the changes of plate boundaries can be moved a week. Can walk, you can also order a bike, motorcycle or car as a carrier.

In the actual measurement may be because of the scene are not familiar with, although the map has changed, but found it difficult to find the change in the wild land. One solution to please the local staff familiar with the situation a guide; Another approach is to detect changes in the house after the GIS system for geographic variation spot center coordinate values, in the wild is difficult to determine if changes in the region, they begun using GPS - navigation function to guide surveyors to reach the approximate location of the measured plots.

In the measurement of changes in land not only to obtain the spatial coordinates, but also to record the changes in the properties of block changes. Property code can be directly input GPS receiver, a maximum of 72 characters. Before the measurement should be numbered so as to avoid all the plots under test measurement omission. In addition, the measurement process in the mobile station and base station should always be to maintain contact, in case problems with the base station to inform mobile station to suspend work.

1.4.4 GPS differential post-processing

As the stand-alone GPS positioning accuracy can not meet the 1:1 million mapping requirements, so there must be differential treatment. County land department, taking into account the technical requirements and financial capabilities, using post-processing differential treatment of mobile station processing the measured values, in order to achieve 2 ~ 5 m accuracy. Differential post-processing techniques rely mainly on software to correct the value and the concept of differential measurements solver, MAGELLAN company supplied MSTAR differential processing software.

1.5 System integration and data visualization

1.5.1 Integrated Platform of choice

Taking into account the county (city) level a user's financial capacity and easy to master the requirements of the hardware and software selection process, according to the following principles: ① able to meet the technical requirements of research projects; ② system is stable and good performance, the user easy to master , use and maintenance; ③ in funding for affordable, easy to promote; ④ easy to integrate the various existing software and hardware resources; ⑤ development cycle should not be too long.

According to the above-mentioned 5-point demands, after a lot of investigation work, initially identified as follows:

Software environment. The WINDOWS95 environment, in order to ARCVIEW as an integrated platform for visualization of GIS software, image processing software and self-developed software for support, the use of macro language, VB, VC + + and other programming languages, development and integration of each functional module, the establishment of dynamic monitoring system software environment.

Hardware structure. Hardware, including GPS receivers, computers (486 and above) and a variety of input and output devices (printers, inkjet plotters).

As the current prices of foreign commercial GIS software is relatively high, so research group is seeking self-made GIS software copyright supporting platform.

1.5.2 GPS data, Coordinate Transformation

Because our land, topographic survey is based on Beijing 54 coordinate system as a reference, while the GPS measurement data is based on WGS84 geocentric coordinate system as a reference, these two coordinate systems used by the reference ellipsoid is different, so the need for coordinate transformation. Different research purposes, accuracy of coordinate transformation are not the same. Differential GPS, due to the work area relative to the GPS control network is smaller, generally less than 50 * 50 square kilometers. Therefore, using two-dimensional plane on the similarity transformation approach.

(1) When there is sufficient working area and Beijing, 54 are known to WGS84 coordinates of the situation, calculate the coordinate transformation of the seven parameters or three parameters (rotation parameters, scale parameters and translation parameters) to coordinate transformation.

(2) When there are three areas of work and Beijing, 54 are known to WGS84 coordinates of control points can be calculated according to the following to 54 coordinate system WGS84 transformation parameters x54 = δx + k1x84 + k2y84 y54 = δy + k1y84 + k2x84 where δx, δy, k1 and k2 for the transformation parameters, the extra 1 point for inspection.

(3) In case there is only one known point, the available base station geocentric coordinates of the point the difference between the coordinates of the Beijing 54 as a translation constant, but this low conversion precision.

(4) When the control point can not obtain precise WGS84 coordinates, you can enter the points in the base station 54 coordinates the Beijing differential calculation, the result is WGS84 and Beijing 54 coordinate a hybrid known as "pseudo-54" coordinates, it is and true there is an error between the coordinates 54. If the coordinate transformation accuracy not ask for much but not have access to accurate control points geocentric coordinate (WGS84), this approach is also feasible. XX suburban districts and counties in the GPS field measurements, we have adopted in many public points to calculate the WGS84 geocentric coordinates to Beijing 54 coordinate conversion seven parameters, using WGS84 coordinates differential base station, and then differential results from the WGS84 coordinate system converted to 54 coordinates Department, to be a mobile station 54 coordinates of the true measured value, while the base station 54 coordinates the use of direct difference, to be pseudo-coordinate values of 54, both of the difference of 1 meter. To prove difficult to obtain adequate public point, the direct use of the base station 54 coordinates differential, and the results can meet the land use dynamic monitoring of the accuracy requirements.

As China's rural 1:10 000 cadastral map is based on 3 ° with a Gauss - Kruger projected onto two-dimensional Cartesian coordinate system, so the data must be projected GPS measurements can be matched with the GIS data. In this project we develop a functional module, whose main function is to read into the MSTAR output differential data to complete the accurate projection conversion and data format conversion, the output Arc / Inf o be able to receive a GEN format.

1.5.3 GPS data with the land survey of the space complex analysis of historical data.

GPS measurement data must be converted into a GIS data formats, such as generating Arc / Info for Coverage skills and land survey data, spatial overlay analysis.

GPS field data obtained by the differential treatment MSTAR software can output data in the following format: IDNOi, Bi, Li (i = 1,2, ..., n) where IDNO for the coordinates of the serial number, B, L, respectively the longitude and latitude coordinate transformation through the projection WGS84 coordinate system will be under the GPS data conversion to Beijing 54 coordinate system, and then write the data to Ar c / Info systems can read the format. Thus we get the 1998 land-use change data layers. Layer will change in the Arc / Info environment, with the 1991 land survey data, spatial overlay analysis, get new status quo of land use layers. The layer attribute table for each data item has a time attribute, representing the 1991 and 1998, changes in the properties. Through the query tool can search for each space target (plot) at different time attributes, such as land-use type, ownership, map spot number. The same time on different attributes of the merger get the status of the new plan period.

Land-use data display, query and output ARCVIEW desktop mapping system with spatial data (vector and raster) display, query, statistics and mapping out a series of functions. Because it is based on the WINDOWS environment, so the operation is simple, can be rich in resources. After our initial development, through the hot key connections to multimedia capabilities to join the system. Qian-Ming Township, experimental work has been done:

① through the query tool can query the size of a Polygon, Figure spot number, ownership and land-use types, and more. For example, in 1991 and 1998 to change the map you can search for any spot in 1998 map area, map spot number, ownership and land-use types, and in 1991 the map spot number, ownership and land-use types. That is aware of the plan the type of plaque in 1991, has now become what type.

② Connect with hot key access to a given map plaques sounds or images, text messages.

③ to the attribute database of conventional management, such as add or delete fields, records and other changes.

④ statistical map display in 1998 and 1991, an area of land-use changes.

⑤ produce special plates, and can be printed.
 
Two basic conclusions

Remote sensing dynamic monitoring of land management is not only an important job content, but also directly related to the sustainable development of the regional economy. Traditional land-use update and management practices do not meet the requirements of the information age, exploring new ways of great significance. From the "six. 5," since the remote-sensing (RS) and geographic information systems (GIS) technology has been developed rapidly, the global positioning system (GPS) since 1993 and applied in various fields has developed rapidly. But how the use of RS, GIS and GPS and other high-tech establishment of large-scale land-use dynamic monitoring of the practical techniques, is a topic worthy of further study. XX suburb through the experiment, largely established based on RS, GIS and GPS technology, new method for dynamic monitoring of land. This method is compared with the traditional method has the following advantages.

(1) the use of remote sensing can take the initiative found that land-use change information to extract the rough region changes in land; while traditional methods can only wait passively by the land-using units or individuals to declare, there is underreporting and failing to report the case, increasing the objective of monitoring sex. In addition, the use of TM data, low cost, better able to find changes in the region, particularly non-agricultural land. In the XX rural pilot project, the township from 1991 to 1998, there were changes in block 106, which found that 98 by means of remote sensing, detection rate was 91%.

(2) GPS as a measurement tool is not only fast and high precision, can be Hou day operations, measurement and easy operation. Take in the XX Township, used in the pilot ProMark X-CM GPS receiver, for example, measurement accuracy of 2 ~ 5 m or less, which is unmatched by traditional methods.
 
(3) as compared with conventional mapping, GIS advantage is recognized. The most important point is that digital maps can be very convenient, fast spatial analysis, synthesis, extraction and modification. And the mapping period is short, and low cost. In addition, the cadastral GIS in everyday management play an important role, rejecting the traditional card management.

(4) GPS measurement data and remote sensing data is stored digitally can be directly imported into a GIS system, map, avoiding the traditional method, multiple transfer painted and Qing painting brings error.

(5) The use of 3 "S" integration of technology can satisfactorily complete the county-level 1:10000 scale dynamic monitoring of land resources for land survey and registration of change provided a new means. Compared with the traditional method, not only improve the accuracy of data acquisition, but also greatly improved the working efficiency.