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How To: Calculate the image width and height attributes for a GET_LAYOUT request

Summary

Height and Width are attributes of the IMAGESIZE tag. IMAGESIZE is used with GET_LAYOUT to specify the size of the output (width and height).

If a layout is exported using ArcMap Server in one of the image formats (JPG, BMP, PNG or GIF), the image width and height used in the GET_LAYOUT request is based on a combinaton of the layout page size set in the ArcMap document and the desired output resolution of the image. To increase resolution, you can increase the output size.

To keep the correct map scale, the width and height must maintain the aspect ratio of the orginal ArcMap document page layout. If the specified width and height deviate from this ratio, ArcMap Server will adjust the width and height values in order to maintain the correct aspect ratio.

Height and width are ignored when the output type is a vector format (AI, EPS, EMF, PDF, or SVG). Use DPI to change resolution.

Procedure

The size of the output image (width Wi in pixels and height Hi in pixels) can be estimated from the page size of the layout being served (width Wp in inches and height Hp in inches) and the desired resolution R in pixels per inch.

Wi = Wp x R

Hi = Hp x R

Note:
Make sure you convert the page size to inches before estimating the image size.

For example, if the page size is 8.5 x 11 inches and the IMAGESIZE tag is not included in the GET_LAYOUT request, the default resolution of 96 DPI is used to calculate the image size.

Wi = 8.5 x 96 = 816 pixels

Hi = 11 x 96 = 1056 pixels

Let's say you want to increase the resolution to 300 dpi for the same 8.5 x 11 inch layout. The image size will be:

Wi = 8.5 x 300 = 2550 pixels

Hi = 11 x 300 = 3300 pixels

Note:
Make sure you have enough memory for your service. For the above example the the image memory limit would need to be at least 34 MB (3300 x 2550*4/1000000 = 33.66)

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