Setting up survey project---→Setting up control points and survey-→ Aerial photography-→Aerial photo scanning →Aerial triangulation survey-→ Statistical contour plotting and mapping-→Frontal image modification--→ Draft editing and checking0-→ Forwarded to checking team for checking and investigation implementations

I.Setting up survey project

1. 1.In accordance with annual statistics on base map survey area and workload, first plan the progress of project, personnel organization, equipment and material preparatory works, collect control point, pictorial-related information.
2. Set up survey area aerial photography project (including air routes and air photo signals at control points planning)
3. Clarify work descriptions and operation details, arrange related information, and set up work project proposal to serve as reference for operation.

II.Setting up control point coordinates and conduct survey

1. All existing control points within survey area (including triangulation
   points,precise guidance line points, satellite control points or anticipated actual survey control points) should set up appropriate control point air photo signals (or air signal for short) and ground control point survey. Control points are to be tidied up to provide open surroundings to facilitate placement of satellite at fixed position and reception of satellite signals. Data acquired should serve as reference for air triangulation adjustments.

III.Aerial photography

1. In accordance with the 1/5000 photo base map center of the island, adopt south-north direction as aerial route.
2. Use half of the 1/5000 photo base map range of 1382 meters as base line for over-lapping photo taking.
3. In conjunction with topographic undulations, the 1/18000 ratio is adopted as basis for aerial route height designing.
4. Based on the 3 principles stated above, around-island aerial routes are planned to be 81 in all. Photo negatives used should be special aerial photography survey used negatives.
5. Method of photography: Perpendicular repeated photo taking, slanting of less than 4 degrees, aerial deflation angle is not to exceed 10 degrees, each aerial route should be taken 2 additional image pictures on both terminals. In order to guarantee air triangular average deviation precision, front to back overlapping may not be less than 60% and not less than 30% from left to right.
6. Weather conditions for good photo taking are: sunny days without clouds, smog, mist or fog, good visibility, and the height of the sun should be higher than 35 degrees to minimize shadowing.
7. After each air photo taking, 2 GPS receptor equipment on airplane and ground base are to calculate main square for each image based on the received data. DEL file derived are provided for future follow up use.
8. Photo negatives after photo taking are to be developed by our bureau and transferred to the Data Office together with relevant data.
9. In order to improve photo quality, photo and negative have to be sharp and clear. Color should be well blended and mild. Image tracking should be under 0.02mm required in mapping. In order to decrease image shadowing in mountainous areas, photo taking timing is to be paid more attention to in the future.

IV. Aerial photo negative filing and scanning

1. Developed negatives will be examined or printed together with data transferring form and SEL file and sent to the Data office (Photo Room) for filing, scanning operations. Actual operation is shown as the two flow charts in the following:

V. Aerial triangulation plotting

1. Aerial triangulation survey makes use of stereoscopic or monoscopic coordinate plotter, precise resolution Stereoscopic plotter, value aerial image work station or other equivalent precision aerial surveyors in surveying known control points and pending control point model coordinates or photo image coordinates.
2. Aerial triangulation photo image tie points are to be distributed in 9 standard point positions of every photo image. 2 photo image points are to be selected for each position, i.e. every photo should contain 18 points, and every image should contain 12 photo points. After aerial triangulation error detection, each standard point should have minimum reserves.
3. Aerial triangulation adjustment may be calculated through the “beam method” or “independent model method”. The least denominator after adjustments may be used in detecting survey value inaccuracies. In the “beam method”, medium error rate should not exceed 15mm, while it may not exceed 20mm(horizontal), and 25mm in vertical.After enforced matching with the ground control point, medium error rate should not increase by more than 30%. In case an increase of 30% or higher occurs, ground control point accuracy should be reexamined.

VI. Statistical contour plotting and mapping

（ I ）、 Value topographic model survey recording

1. Topographic model value may be directly plotted and recorded by using precision resolution stereographic plotter, value aerial plotting image work station or other equivalent aerophotogrammetric mapping instruments. It may also be calculated using statistical contour data calculations, or digital image automatic matching method.
2. Topographic model value vertical point distribution adopts the “square image point method”. Interval stands at 4mm above image. (20meters off ground), topographic features should be mapped out (such as mountain peak, depression, saddle variation). Topographic feature lines (such as mountain ridge, valley, and steep hill.) and topographic fault lines (extreme ground tilting angle variations in boundary demarcation lines) data are to be mapped out as well.
3. Result data of topographic model value is considered as the actual vertical of ground surface. This height is derived by deducting ground coverings (such as trees, buildings etc).As ortho image adjustment vertical control of topographic model data, ground covering height is included, interval stands at within 2mm above image (10 meters off ground).
4. Value topographic model data is in American data exchange standard code format（ASCII）, recorded in CD computer magnetic media to produce value topographic data file. Value topographic data file should be coordinated with base map file. Each picture is saved in one file.

( 2 ) Statistical contour survey mapping

1. Statistical contour may be surveyed and mapped by using precision digital plotter, value aerial image work station or other equivalent aerophotogrammetric mapping instruments in direct plotting or by using value toptograhic model data, computer software input calculations to produce results.
2. Statistical contour of 5-mter intervals between level ground and hill; and 10-meter in high mountain area, should be made into statistical contour file and recorded in CD computer magnetic media. Statistical contour should be sequential and non-interrupted when encountering ground objects. However, during plotting and mapping by statistical contour, in order to ensure readability and clarity of ground objects in picture, suitable editing is required.
3. Statistical contour is the actual display of vertical，during plotting and mapping, ground coverings should be deducted (such as trees, buildings etc). Statistic topographic model data input calculation is thus derived. Topographical features should be considered as well as data of topographic lines and faults.
4. When using statistic topographic model data input to calculate statistical contour or vice versa, special attention should be paid to statistic base map accuracy requirements. No repeated calculations may be derived.
5. During statistic topographic model testing, mapping and plotting of statistic contour, several vertical checking points should be measured for accuracy checking purposes

VII、Ortho image modifications

1. By means of statistic aerial image mapping work station or other equivalent aerophotogrammetric mapping instruments, together with statistic topographic data as ortho image vertical control data, center projection of aerial images are modified point by point into ortho image projections. Projection errors are deleted and made into digital ortho image data file to be recorded in CD computer magnetic media.
2. Ortho image modification makes use of statistic topographic model data including horizontal and vertical of ground coverings. Interval stands at within 2mm above picture image (10meters off ground).
3. Digital ortho image is represented by black and white images.
4. Digital ortho image data file is saved in TIFF format and is coordinated with base map file. Each picture image is saved in `1 file.

In addition, high resolution stereoscopic plotter, statistic aerial image work station or other equivalent aerophotogrammetric mapping instruments, are used to under go plotting and mapping in layered fashion. Content of mapping include main traffic system on picture image, water system is to be mapped out to and layered in classified codes; produce quantity-oriented data file saved in 2 formats namely AutoCAD DXFand MicroStation DGN. Each photo image is saved in 1 file. Classified code listing include 10 basic topographic data namely: survey control point, administrative boundary, building, traffic system, water system, public business web, plantation covering, landform, statistic topographic model, image reorganization and remark.

VIII、Draft mapping editing and checking

Acquire ortho image and 2D contour data, and by means of digital ortho data file, and quantity-oriented data, draft mapping, editing and checking are performed. Main job descriptions are as follows:

1. Establish image checker lines and scope. Delete contours and water lines outside scope.
2. Imaging, image reorganization, positioning and outlining arrangements by triangulation of contour. Satellite positioning at right positions and edit.
3. Image size and color adjustments. Check if neighboring boarders of images are true and correct.
4. After image editing, various data and content accuracy are carefully checked. Errors are modified before final image release.
5. After checking, draft map is sent to Photoshop for photo development and printing to be bonded into final draft for checking purpose.
6. Check printed final images and sent them to “Examining Squad” for checking purpose.
7. Forestry area checking draft Provided for the Examining Squad had received feedbacks that they were generally too dark, overlapping contours could not be determined. After editing, colors were adjusted, with brighter and more consistent hues and images