how to symbolize a '0' value as null in arcpad

Question

I have 2 .sid images that we use in ArcPad. Where the images overlap, there is a blackout area where there is a '0' value from the projections. In arcMap, I can simply symbolize a '0' value as null and eliminate the black-out. They are both projected into the same state plane system, even though the boundary is through one of the images. This means that the projection extent is exceeded, and therefore the images cannot be mosaiced. I cannot reproject one nor the other both because of the boundary of the State-Plane system, and everything has to have the same coordinate system in ArcPad. Any suggestions?

Thank you!!

FaithWebster · Answer

Hi Stephen,

Thanks for replying. I will see about converting to a .tiff, it may be prohibitively large in that format. I am also looking into a solution to the blackout via mosiacing. I will also bring up the possibility of tech support. We are government based so Tech support is different somehow. I'm not sure exactly; I'm new here.

StephenQuan1 · Answer

Hi Faith,

Some of the raster formats define transparency better than others.

I'm not sure if MrSID files offers an alpha channel, but, if it does, you can try setting it to transparency for your '0' value pixels.

Typically if ArcPad sees a 4th band, it will treat that as an alpha channel.

Some other formats that support alpha transparency channel are TIFF, PNG and GIF. I feel silly in suggesting this because I understand the point of MrSID is the attactiveness of the super compact compression factor. But, if you are open to it, perhaps you can give one of the other formats a try.

ArcPad's TIFF format has received the most attention in terms of patches and updates, so, I would expect it to be the go to format today in terms of speed, memory utilization and rendering.

Another strategy for you to try is tech support. You can consider raising an issue and/or enhancement request to treat a specific value as "null". Some software may allow you specify a specific colour, say, blackness "#000000" or whiteness #ffffff as transparent. It could be a config file say, filename.sid.json, { transparentColor: "#000000" }.

Stephen