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An estimated 5,000,000 images made since the 1920's in the European archives represent an enormous amount of data which may never be recaptured under controlled conditions. It is the goal of AirPhoto to deal with this kind of image within the limits of the data and the financial limits of most archaeological institutions and private investigators by non-photogrammetrists.
AirPhoto provides a useful tool for archaeologists (and others) without large amounts of money to spend on user-hostile photogrammetric hardware or expensive software which will enable them to deal with a reasonable number of the many aerial images which have accumulated over the years using modest PC's and peripherals.
What AirPhoto does:
AirPhoto makes orthophotos from scanned extreme obliques and superimposes scanned maps on them in various ways. It is not a photogrammetric plotting program, but it is a true orthophoto program working from a digital terrain model (DTM) if desired, although the DTM is not required. A DTM may be imported or the program can create one from a collection of manually entered or imported irregular heights. It is designed to give a very fast result with a minimum of handwork apart from the entry of corresponding control points in a picture and a map just by clicking the mouse. Color or black and white images of various formats may be used or obtained directly from a scanner. Any number of maps may be combined to obtain a result for pictures which show data contained within more than one map. Mosaics may be made from multiple color or black and white images. The map may be overlaid in black or white with the image(s) or combined with them to give best visibility. If desired, a mosaic may be made with a neutral background for processing elsewhere.
Another goal for AirPhoto is to avoid as much human interaction with the data in the images as possible. The idea is to use extreme oblique images and overlay them with a base map or maps as output if desired. Other applications are also possible. It is primarily intended for images made with uncalibrated hand-held normal cameras. It also includes transformations for dealing with some kinds of satellite or scanner imagery and for images made in hilly terrain without a digital terrain model.
AirPhoto offers full color image processing, an unlimited number of control and calibration points, an unlimited number of windows on the screen at once (hardware dependent), extremely rapid processing and a large variety of options. There are no numbers to be entered anywhere unless manual control has been deliberately selected. All options and previous program states are recorded and played back when the program is restarted.
AirPhoto also offers calibrated mapped output in any of a large number of national and international coordinate systems.
What AirPhoto does not do:
AirPhoto is a multiple document interface (MDI) Microsoft Windows program which runs only under Windows NT/2000/XP/Vista on Intel processors. It is not offered for other hardware platforms or operating systems.
AirPhoto is not intended to compete with high accuracy high priced user- hostile photogrammetry packages requiring knowledge of photogrammetric principles. Most archaeological air photos have been made with uncalibrated cameras under uncontrolled conditions with inadequate numbers of control points, so only a fairly useful semi-quantitative result is possible. Nonetheless, sub-meter accuracies are usually obtainable with good control points.
It is not intended for making site plans which are essentially based on subjectively extracted data from photos put into maps. AirPhoto has no option for subjective choice of information apart from the choice of control points, it's WYSIWYG (what you see is what you get).
Why use AirPhoto?
It is much faster than a photogrammetric plotting program and is without any subjectivity in the interpretation of data by the user. The disadvantage is that it is not easy to incorporate data from many photographs taken over many years under widely varying conditions at least in the present version, although you may make photomosaics from these in black and white or in color.
It will not deliver a black and white site plan although an approximation to one is possible using built-in filtering functions. It only delivers a new image in color or in grayscale, geometrically corrected to fit the map data as a guide to where things are. If desired, the aerial image may be enhanced and transformed into a black and white drawing which, after rectification may be manually edited with a standard drawing programme to remove anything which is not of interest. It does not deliver the abstraction from reality which a plan constitutes. The user then has to make his own decision about the information thus presented and perhaps use the output in a CAD or GIS, or drawing package to superimpose his interpretation on the geometrically corrected data if desired.
Hardware and software requirements:
Windows NT 4.0/2000/XP/Vista with at least 128 MB of physical memory. A Pentium, Pentium Pro or Pentium II, III or IV processor is required. Although the programme may install and even run under Win9x/ME, support for these operating systems is no longer available.
Performance is optimal with 512 MB or more memory. The virtual memory setting of the machine should be set to at least 512 MB, preferably more. You should defragment your hard disk before changing the virtual memory setting.
You also need a good high-resolution scanner to enter data. A flatbed or slide scanner with at least 300 dpi and 24 bit color resolution is recommended if you wish to process color airphotos. It is advisable to check the geometric accuracy of a scanner-laser printer combination by scanning a map, printing it at 1:1, then holding the output print over the original on a light table to see if errors are acceptable. If you use a slide scanner for airphotos and a flatbed scanner for maps, it is very important to check for possible geometric incompatibilities. Currently, the program has no facility for calibrating a scanner/printer combination.
It is advisable to have a display with at least 1024x768 or higher resolution, but the program will work with displays having lower resolution down to 800x600..
You should use the fastest, most modern display card available. It should have as much local memory as offered by the manufacturer if you want to treat large images. If you have an older display card, you may experience temporary smearing when entering control points using a unique magnifying window. This is due to slow refresh in such cards and cannot be corrected via software. AirPhoto supports dual monitor display cards directly and this configuration is optimum for production environments. Two LCD panels with a dual head card or dual display cards permit display of map and image on each screen separately as well.
Structure, Functions and Operations:
Each window displays a separate image. Each image is a separate object. The number of windows and images is limited only by hardware. All appropriate operations may be applied to any image. The images in the windows may be loaded directly by using a Twain compliant scanner operated from Airphoto or from a disk file of a previously scanned image.
Image formats may conform any one of the following standards: Windows Bitmap (.bmp), Tagged Image File Format (.tif), with or without various kinds of compression and colour space representation, Jpeg (.jpg) with smoothing and compression control, Jpeg 2000, Png (.png), Tga Targa (.tga), Pcx (.pcx), Earth Resource Mapping (.ecw) Windows Metafile (.wmf), enhanced Metafile (.emf), GeoTiff and DXF. Different formats may be loaded in multiple windows. The images are converted during loading to a common internal bitmap format using 24 bits regardless of the source. All processing is carried out on this intermediate format. Output may be in any of the input formats. An Import/Export utility permits loading and writing a large variety of more exotic file formats. Only Import/Export does not support geographic referencing.
The program combines one or more image with one or more other images with correction of the geometry of the source to fit the target. The source images may be superimposed, merged or mixed in various ways with the target images. Sources and targets may be any kind of scanned image. The usual application is for transformation of an oblique aerial image to fit a scanned map. It is also possible to fit and superimpose oblique images to scanned vertical images, or to fit historical maps to accurate modern maps. There are no restrictions on the kinds of images used for sources and targets.
Multiple source images may be used to make a photomosaic on a target image. Images may also be accurately aligned to regularly spaced points in a new empty image. This function is usually used for joining adjacent scanned map sheets, needed when the content of an aerial image extends over the limits of a single map. A transformation is used from the source to the target in this join operation to correct for paper map and scanner distortion. The result from one or more join operations may then be saved to disk and used as a target for all other operations.
Limitations and Precision:
There is no limit under Windows NT/2000/XP/Vista other that those imposed by the display card memory and its driver. When joining images, the maximum size of a resulting image may not exceed the limits imposed by the hardware and the operating system. These limits are imposed by the standards for the Windows memory mapped files used for internal computation. Memory and swapping file space limits will usually be reached on all but the largest machines before this limit is encountered. Precision is mainly dependent on the accuracy of the scanner used, and usually is far less than the internal precision used in calculation.
A number of identical points (control points) in the source and the target must be selected so that a geometric transformation between the source to the target is possible. Control points are selected interactively by using a floating magnifying window or a special cursor. Control points may be deleted, moved or temporarily disabled so that they don't affect calculations if desired. There is no limit to the number of control points, and a larger number will increase the accuracy of fitting the source to the target. Off-screen control points can be selected if two off-screen intersecting linear features are visible on scren.
The windows are shown at 1:1 pixel resolution of screen to scanner by default. Zooming up to a limit imposed by available physical memory as well as dragging is offered. A temporary overview for each window is generated to aid navigation since only a part of the input image is usually visible at normal screen resolutions. An alternative user mode permits displaying the overview of the whole image and zooming into an enlarged view if selected. Control points are labelled either automatically or manually and are stored in a separate (.ctl) file. The file is updated when a window is closed or if the user clicks on the Save icon or menu entry. Multiple control point files may be made for a single image or a single control point file may be used for different images. The appropriate control point file must be selected by the user when opening a new image.
A choice of various transformation options is offered which may take height information implictly or explicitly into account if desired. The position of an output picture element (pixel) is calculated in the input image and the gray or color value is interpolated from the nearby points in the input image. Several different interpolation schemes offering increasing accuracy are offered. All transformation and interpolation options may be used on colour as well as on grayscale imagery. Choice of transformation may be made manually, or the programme may be permitted to choose an optimal transformation based on the number of available control points.
An image may be calibrated in any one of a large number of geographic coordinate grid systems if desired. At least four calibration points are required for this purpose. More may be used to increase the accuracy of calibration and to compensate for scanner and paper map distortion. A calibrated scanned map may be aligned to the chosen grid system if desired. When an image (usually a map) has been calibrated, the position of the mouse cursor is show in in the units of the chosen grid system in a status bar at the bottom of the image. It is possible to convert from any of the supported systems to the GPS (Global Positioning Satellite) system and from that to any other system. This may be used for datum transformation between two adjacent national grids, or between any of the supported international grids.
Calibration is automatic when a GeoTiff file containing data from one of more than 40 supported national or international grids is loaded. Similarly, calibration is also automatic if ArcView, MapInfo or ERmapper have been selected.
If one has been selected, a file with the information required by a Geographic Information System will be written to a separate file when the window is closed containing the parameters which each of the supported types of GIS require. Currently, files are written for ArcInfo/View, MapInfo, ERmapper and Idrisi as well as fully qualified GeoTiff.
The calibration points are shown on the screen prefixed with the letter C to distinguish them from control points. They are stored in a separate calibration file (.cal). This is automatically reloaded when a new file is selected. It must reside in the same directory as the image itself.
All grid systems can be converted to and from GPS coordinates. This also permits datum transformations between them using either Helmert 3D (Bursa-Wolff) or Molodensky methods.
Digital Terrain Model (DTM):
The program will make a DTM from known heights on a scanned and calibrated map or from an imported Digital Elevation Model (DEM). The heights need not be at control or calibration points. Only a few are required. If available, an ascii file with heights and their map coordinates in the calibrated map grid system may be used instead. The DTM will be displayed as a three dimensional surface which may be rotated and examined from all directions. The surface may also be lit and displayed with variation of the lighting position, or it may be displayed as a contour map. The result may be saved as a separate image for other use. The DTM facility may also be used to display irregularly spaced geophysical or any other kind of measurement data which is three dimensional, independently of the aerial photography function of the program. There is no limit to the number of heights used in making the DTM, nor need they be regularly spaced. The special formats DTM of the UK Ordnance survey are supported.
Speed has been optimized and is possibly higher than that of any competing product. For example, a 3.5 MB full color air photo can be superimposed on a scanned map in less than 0.1 second with a 2.4 Ghz Pentium IV machine.
How to download and install it:
AirPhoto is contained in one self-installing file, Airfoto3.exe
Test data is contained in Airdata.exe.
AirPhoto is shareware. A secure encrypted registration program is contained in Airegister.exe along with a help file containing all details
After downloading the file, simply run the executable to expand the compressed setup files and start the installation.
After completing setup, install the test data and registration program if you wish to do so.
If you have installed a previous version of AirPhoto, use the Remove programs options to uninstall before you start.
What to do first after installation:
Start the program and read the help file first. A shortcut to Airphoto.hlp is created on the start menu, so that you can read it without running the program. There are no time limits on the help file. If you prefer, you may also download the help file in HTML format and read it with your Web browser.
A special network registration code permits installation on an unlimited number of machines with a metered number of simultaneous users. Only the metering code is installed on the network server.
Summary of features
Maximum number of control points: unlimited
Minimum number of control points: 3
Control point determination through intersection of linear features: yes
Automated control point 'tweaking' to improve precision: yes
Control/Calibration/Height point entry and numbering: manual/automatic, id number displayed on screen
Disabling of Control/Calibration/Height points: single click toggle on/off with colour change
Moving of control points: mouse drag or single pixel with keypad
Maximum number of DTM-DEM heights: unlimited
DTM computing algorithm:
Nlog2(N) Sibson Natural Neighbour.
DTM display: yes, with lighting and contours in colour, output to Windows bitmap, WMF and extended EMF files. Rotation, scaling and shift of DTM model interactively with the mouse. User modification of colours, contour intervals and more.
DTM Import/Export: both
Number of transformation options: plane projection (colinearity), polynomial (up to 5th oder), multipoint (up to 5th order), Fischler-Bolles with DTM, Local Goshtasby affine triangle stretch optimisation after multi-point transformation (for stretching old maps to new ones).
Number of colours, on display and in files:
2, 16, 256, 16M
Image Interpolation options:
3 (Near Neighbour, Bilinear, Bicubic spline, also in colour)
File formats (Input/Output):
Tiff, Tiff variously compressed, GeoTiff, JPEG with various colour options, JPEG 2000, ERmapper ECW, BMP, Png, Png Interlaced, PCX, Targa, WMF, EMF,
DXF, AutoCad 12 compatible, input only.
Display overlay formats: 5 + DXF
Number of National Grids:
over 50 including lat/lon (degrees or decimal), XY decimal Grid coordinates on screen jump over UTM, Gauss-Krueger and Lambert Conformal boundaries where required.
Measurement of geodetic distances and areas of irregular polygon shapes.
AirPhoto offers direct support for the national grids in Setup of:Overlay grid in any of the chosen systems, even over meridian or latitude strip boundaries.
forward/backward to all national grids and UTM via Helmert, Bursa-Wolff or Molodensky transformation, datum transformation of latitude/longitudes of all supported grids.
Maximum Image Size:
limited only by virtual memory and display card drivers under WindowsNT/2000/XP/Vista.
Number of simultaneous images on screen:
nearly unlimited under WinNT/2000/XP/Vista
Project support, history list: yes, unlimited number of images, control, calibration, heights under WinNT/2000/XP/Vista
Map joining for photos which overlap map boundaries: any number simulataneously. Alternatively via transformation to a large blank file created by the program, unlimited.
Mosaics from an unlimited number of rectified images with retention of all control, height and calibration information.
Overlay of maps on mosaics.Google Earth images with automatic calibration in any chosen grid.
Blank maps with control point transfer: yes, also fixed sizes and background colours
Context sensitive Help: for all dialog boxes. hints for all buttons and toolbits on toolbars.
Direct scanner support: yes, industry standard TWAIN. Alignment and compensation for paper shrinkage, rotation and scanner distortion with calibrated maps.
File size, type, compression and colour analysis:
including GeoTiff information for all European Petroleum Survey Ggroup (ca. 1400 +) documented grids.
scale, rotate, rotate decimal, 5 x filtering, colour correction, clip, adaptive thresholding, fine detail enhancement (Wallis), thresholded Median filtering, 'bump' mapping, thinning, thickening.
Printing to scale: absolute, relative scaling
Interactive rectified area selection
Detail in Image: Variable magnification cursor, for control, calibration & heights, decimal zoom.
GIS Support: ArcView, MapInfo, Idrisi, DXF, GeoTiff (all EPSG grids), ERmapper.
Transformation Undo: unlimited
Image processing Undo: unlimited
Automated industry standard installation programme: InstallShield clone, Microsoft standard for Add/Remove Programs in Control Panel.
Program state preservation:
All options chosen at last program usage recorded to disk file and recalled on restarting. Current state displayed on status line if wanted. A project file can be created at any time and 'played back' to restore the total state at any moment. History list of projects on File menu.
Import/Export of control and height data:
Import/Export, append, load from image Excel-like grid editor
Internet download, 3 ftp mirrors.
no charge within major version, automatic e-mail notification when available
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Last update: April 20, 2009