These sheets allow the definition of any geometry by means of a pixel map.
An important feature of the procedure used here is that, by choosing one of three sheets, you can specify how to handle the single row of pixels that's all around the periphery of the image.
1)With the first sheet all pixels in the image are kept entirely: this is a normal procedure, but in many cases can give unsafe results. To be used if you know that the pixel map exactly represents the geometry of your section.
2)With the second sheet the row of pixels at the periphery is considered effective only at 50%. This will often give best approximate results. To be used for example when the image has been prepared in a drawing application, by drawing a closed line representing section's geometry, then filling it.
3)With the third sheet the row of pixels at the periphery is completely removed. This will generally give conservative results.
User defined section: instructions
Closely follow the following steps to obtain the best results from this application. Below you find a more detailed description, that you'll need to know only rarely under special circumstances.
1) The file defining the section to be analyzed must be prepared by means of a suitable drafting software: as an example, AutoCadŽ allows for creating a .BMP file from any drawing.
2) The graphics file must be in one of the available formats: .BMP , .PNG , .GIF , .JPEG.
3) In creating the image file use afap 2 colors only: white for the background and black or any dark color for the foreground. The solid region defining the section must be in the foreground color. No other elements not pertaining to the section may be present.
4) At this point get into www.xcalcs.com, login, open the sheet you copied from 'My section', click the blue image to the right of the figure, and, in the forthcoming dialog, input the name of the file prepared as above. Click OK to upload the image and submit it (and please be patient if the image is large)
5) If there were no problems, the sheet is reloaded and you'll see your image in blue appearing to the right of the figure: you'll need only to define the height of the section to get what you were looking for.
User defined section: more information
This calculation sheet is for determining inertial properties of a section defined by a pixel map. More information upon calculation methods may be obtained upon request: in this event please always specify the reason for the request (perhaps an unexpected result). The precision of results will of course depend also on image resolution: a typical image 256x256 pixels will be sufficient for most applications.
The image file to be analyzed must be structured in order to allow for recognizing, among all colors included, the colors representing the background and those representing the foreground (the actual section); this application considers as the foreground any color with a brightness (R+G+B) smaller than 50%, and the other colors are the background.
If you get a fully white or a fully blue image, or another unexpected result, there was likely a problem in the color recognition: get a 2 color image to avoid any misinterpretation.
Please note also:
- any transparency is ignored
- any white padding around the solid section is removed during file analysis
- you shall be able to define the section dimensions in the calculation sheet.
- the aspect ratio (ratio of horizontal to vertical pixel density) will always be 1, even if your file specifies something different: you should account for that in building your image - .BMP files cannot be compressed (compression may be referred to as 'RLE' in your software).